Multiphoton Processes

All-inorganic CsPbBr 3 perovskite colloidal quantum dots have recently emerged as a promising material for a variety of optoelectronic applications, among others for multiphoton-pumped lasing. Nevertheless, high irradiance levels are generally required for such multiphoton processes. One strategy to enhance the multiphoton absorption is taking advantage of high local light intensities using photonic nanostructures. Here, we investigate two-photonexcited photoluminescence of CsPbBr 3 perovskite quantum dots on a silicon photonic crystal slab. By systematic excitation of optical resonances using a pulsed near-infrared laser beam, we observe an enhancement of two-photon-pumped photoluminescence by more than 1 order of magnitude when comparing to using a bulk silicon film. Experimental and numerical analyses allow relating these findings to near-field enhancement effects on the nanostructured silicon surface. The results reveal a promising approach for significantly decreasing the required irradiance levels for multiphoton processes being of advantage in applications such as biomedical imaging, lighting, and solar energy.

All-inorganic CsPbBr 3 perovskite colloidal quantum dots have recently emerged as a promising material for a variety of optoelectronic applications, among others for multiphoton-pumped lasing. Nevertheless, high irradiance levels are generally required for such multiphoton processes. One strategy to enhance the multiphoton absorption is taking advantage of high local light intensities using photonic nanostructures. Here, we investigate two-photonexcited photoluminescence of CsPbBr 3 perovskite quantum dots on a silicon photonic crystal slab. By systematic excitation of optical resonances using a pulsed near-infrared laser beam, we observe an enhancement of two-photon-pumped photoluminescence by more than 1 order of magnitude when comparing to using a bulk silicon film. Experimental and numerical analyses allow relating these findings to near-field enhancement effects on the nanostructured silicon surface. The results reveal a promising approach for significantly decreasing the required irradiance levels for multiphoton processes being of advantage in applications such as biomedical imaging, lighting, and solar energy.

Native hyaline cartilage from a human knee joint was directly investigated with laser scanning microscopy via 2-photon autofluorescence excitation with no additional staining or labelling protocols in a nondestructive and sterile manner. Using a femtosecond, near-infrared (NIR) Ti:Sa laser for 2-photon excitation and a dedicated NIR long distance objective, autofluorescence imaging and measurements of the extracellular matrix (ECM) tissue with incorporated chondrocytes were possible with a penetration depth of up to 460 µm inside the sample. Via spectral autofluorescence separation these experiments allowed the discrimination of chondrocytes from the ECM and therefore an estimate of chondrocytic cell density within the cartilage tissue to approximately 0.2-2•10 7 /cm 3 . Furthermore, a comparison of the relative autofluorescence signals between nonarthritic and arthritic cartilage tissue exhibited distinct differences in tissue morphology. As these morphological findings are in keeping with the macroscopic diagnosis, our measurement has the potential of being used in future diagnostic applications.

We have developed a new descanned parallel ͑32-fold͒ pinhole and photomultiplier detection array for multifocal multiphoton microscopy that effectively reduces the blurring effect originating from scattered fluorescence photons in strongly scattering biological media. With this method, we achieve a fourfold improvement in photon statistics for detecting ballistic photons and an increase in spatial resolution by 21% in the lateral and 35% in the axial direction compared to single-beam non-descanned multiphoton microscopy. The new detection concept has been applied to plant leaves and pollen grains to verify the improvements in imaging quality.

This study demonstrates a measurement system for a non-degenerate two-photon absorption (NDTPA) spectrum. The NDTPA light sources are a white light super continuum beam (WLSC, 500 ∼ 720 nm) and a fundamental beam (798 nm) from a Ti:Sapphire laser. A reliable broadband NDTPA spectrum is acquired in a single-shot detection procedure using a 128-channel lock-in amplifier. The NDTPA spectra for several common laser dyes are measured. Two photon absorption cross section enhancements are found in the experiment and validated by theoretical calculation for all of the chromophores.

We address the concept of direct multiphoton multiple ionization in atoms exposed to intense, short wavelength radiation and explore the conditions under which such processes dominate over the sequential. Their contribution is shown to be quite robust, even under intensity fluctuations and interaction volume integration, and reasonable agreement with experimental data is also found.

We characterize the nonlinear optical response of low loss Si 0.6 Ge 0.4 / Si waveguides in the mid-infrared between 3.3 μm and 4 μm using femtosecond optical pulses. We estimate the three and four-photon absorption coefficients as well as the Kerr nonlinear refractive index from the experimental measurements. The effect of multiphoton absorption on the optical nonlinear Kerr response is evaluated and the nonlinear figure of merit estimated providing some guidelines for designing nonlinear optical devices in the mid-IR. Finally, we compare the impact of free-carrier absorption at mid-infrared wavelengths versus near-infrared wavelengths for these ultra-short pulses.

We present a review of theoretical and experimental aspects of multiphoton quantum optics. Multiphoton processes occur and are important for many aspects of matter-radiation interactions that include the efficient ionization of atoms and molecules, and, more generally, atomic transition mechanisms; system-environment couplings and dissipative quantum dynamics; laser physics, optical parametric processes, and interferometry. A single review cannot account for all aspects of such an enormously vast subject. Here we choose to concentrate our attention on parametric processes in nonlinear media, with special emphasis on the engineering of nonclassical states of photons and atoms that are relevant for the conceptual investigations as well as for the practical applications of forefront aspects of modern quantum mechanics. We present a detailed analysis of the methods and techniques for the production of genuinely quantum multiphoton processes in nonlinear media, and the corresponding models of multiphoton effective interactions. We review existing proposals for the classification, engineering, and manipulation of nonclassical states, including Fock states, macroscopic superposition states, and multiphoton generalized coherent states. We introduce and discuss the structure of canonical multiphoton quantum optics and the associated one-and two-mode canonical multiphoton squeezed states. This framework provides a consistent multiphoton generalization of two-photon quantum optics and a consistent Hamiltonian description of multiphoton processes associated to higher-order nonlinearities. Finally, we discuss very recent advances that by combining linear and nonlinear optical devices allow to realize multiphoton entangled states of the electromnagnetic field, either in discrete or in continuous variables, that are relevant for applications to efficient quantum computation, quantum teleportation, and related problems in quantum communication and information.

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Ex vivo human skin has been used extensively for cosmeceutical and drug delivery studies, transplantable skin allografts, or skin flaps. However, it has a half-life of a few days due to ischemic necrosis. Traditional methods of assessing viability can be timeconsuming and provide limited metabolic information. Using multiphoton tomography and fluorescence lifetime imaging ͑MPT-FLIM͒ we assess ischemic necrosis of ex vivo skin by NAD͑P͒H autofluorescence intensity and fluorescence lifetime. Ex vivo skin is stored in the presence and absence of nutrient media ͑Dulbecco Modified Eagle Medium͒ at −20, 4, and 37°C and room temperature over a 7-day time course to establish different rates of metabolic deterioration. At higher temperatures we observe a decrease in NAD͑P͒H autofluorescence, higher image noise, and a significant increase in the average fluorescence lifetime ͑ m ͒ from ϳ1000 to 2000 ps. Additionally, significant distortions in NAD͑P͒H fluorescence lifetime histograms correspond to the reduction in autofluorescence. Skin kept at 4°C, with or without media, showed the least change. Our findings suggest that MPT-FLIM enables useful noninvasive optical biopsies to monitor the metabolic state and deterioration of human skin for research and clinical purposes.

We present a method for calculating a two-dimensional refractive index field from measured boundary values of beam position and slope. By initially ignoring the dependence of beam trajectories on the index field and using cubic polynomials to approximate these trajectories, we show that the inverse problem can be reduced to set of linear algebraic equations and solved using a numerical algorithm suited for inverting sparse, ill-conditioned linear systems. The beam trajectories are subsequently corrected using an iterative ray trace procedure so that they are consistent with the ray equation inside the calculated index field. We demonstrate the efficacy of our method through computer simulation, where a hypothetical test index field is reconstructed on a 15 × 15 discrete grid using 800 interrogating rays and refractive index errors (RMS) less than 0.5% of the total index range (−) are achieved. In the subsequent error analysis, we identify three primary sources of error contributing to the reconstruction of the index field and assess the importance of data redundancy. The principles developed in our approach are fully extendable to three-dimensional index fields as well as more complex geometries.

Bu calismada, yuksek guclu femtosaniye laserle birlikte TOF-MS kullanilarak Cn topak molekullerinin ve ozellikle C60 fullerene molekulunun uretimi ortaya konmaktadir. Buna ilave olarak kutle spektrumundaki pik deseninin laser gucune bagliligi ortaya konmaktadir. Kutle spektrumunda C60molekulunun fragmentasyon desenindeki Cn+, (n=1….24) iyonlarinin ve ana iyonun elde edilmesi calisilmistir. Bu tur iyonlastirma surecinde dalgaboyuna ve laser gucune bagli olarak femtosaniye kisa laser pulslari kullanilarak molekuler iyon elde edilebilmektedir. Ayni zamanda hedef olarak grafit kullanilmak suretiyle Cn+ (n=1…60) karbon topaklarinin birlesme yoluyla elde edilmesine calisilmis ve elde edilen spektrum analiz edilmistir. %99,5 saflikta C60 molekulunun ve grafitin bir hedef numune olarak kullanildigi bu calismada, dusuk laser yogunluklarinda alinan kutle spektrumunda cok kucuk bir ana iyon gozlenmistir. Bu calismada, 800 nm dalga boyu icin yaklasik olarak 1012-14 W/cm2 laser yogunluklari kull...

Vocal fold scarring as a result of injury or disease can lead to voice disorders which can significantly affect the quality of life. During the scarring process, the normally elastic tissue of the vocal fold lamina propria is replaced by a much stiffer collagen-based fibrotic tissue, which impacts the fold's ability to vibrate. Surgical removal of this tissue is often ineffective and can result in further scarring. Injectable biomaterials, a form of tissue engineering, have been proposed as a potential solution to reduce existing scars or prevent scarring altogether. In order to properly evaluate the effectiveness of these new materials, multiphoton microscopy emerges as an effective tool due to its intrinsic multiple label free contrast mechanisms that highlight extracellular matrix elements. In this study, we evaluate the spatial distribution of collagen and elastin fibers in a rabbit model using second harmonic generation (SHG), third harmonic generation (THG) and two photon autofluorescence (TPAF) applied to unlabeled tissue sections. In comparison to traditional methods that rely on histological staining or immunohistochemistry, SHG, THG and TPAF provide a more reliable detection of these native proteins. The evaluation of collagen levels allows us to follow the extent of scarring, while the presence of elastin fibers is thought to be indicative of the level of healing of the injured fold. Using these imaging modalities, we characterize the outcome of injectable biomaterial treatments in order to direct future treatments for tissue engineering.

New imaging techniques using near-infrared ͑NIR͒ femtosecond lasers ͑fs-lasers͒ in multiphoton laser scanning microscopy ͑MPLSM͒ have great potential for in vivo applications, particularly in human skin. However, little is known about possible risks. In order to evaluate the risk, a "biological dosimeter" was used. We irradiated fresh human skin samples with both an fs-laser and a solar simulator UV source ͑SSU͒. DNA damage introduced in the epidermis was evaluated using fluorescent antibodies against cyclobutane-pyrimidindimers ͑CPDs͒ in combination with immunofluorescence image analysis. Four fs-irradiation regimes ͑at 800-nm wavelength͒ were evaluated differing in laser power and step width of horizontal scans. Fs-irradiation did not give CPDs at 15-mW or 30-mW irradiation power using 10 horizontal scans every 5 microns. CPDs could be seen at 60-mW laser power and 5-m step size and at 35-mW using 1-micron step width. Quantitative comparison of SSU-induced CPDs showed that the 60-mW laser irradiation regime is comparable to UV-irradiation, giving 0.6 minimal erythemal dose ͑MED͒. The 1-micron irradiation regime was comparable to 0.45 MED. Under these experimental conditions, the risk of DNA damage due to fs-laser irradiation on skin is in the range of natural UV-exposure.

Bu çalışmada, yüksek güçlü femtosaniye laserle birlikte TOF-MS kullanılarak C n topak moleküllerinin ve özellikle C 60 fullerene molekülünün üretimi ortaya konmaktadır. Buna ilave olarak kütle spektrumundaki pik deseninin laser gücüne bağlılığı ortaya konmaktadır. Kütle spektrumunda C 60 molekülünün fragmentasyon desenindeki C n + , (n=1….24) iyonlarının ve ana iyonun elde edilmesi çalışılmıştır. Bu tür iyonlaştırma sürecinde dalgaboyuna ve laser gücüne bağlı olarak femtosaniye kısa laser pulsları kullanılarak moleküler iyon elde edilebilmektedir. Aynı zamanda hedef olarak grafit kullanılmak suretiyle C n + (n=1…60) karbon topaklarının birleşme yoluyla elde edilmesine çalışılmış ve elde edilen spektrum analiz edilmiştir. %99,5 saflıkta C 60 molekülünün ve grafitin bir hedef numune olarak kullanıldığı bu çalışmada, düşük laser yoğunluklarında alınan kütle spektrumunda çok küçük bir ana iyon gözlenmiştir. Bu çalışmada, 800 nm dalga boyu için yaklaşık olarak 10 12-14 W/cm 2 laser yoğunlukları kullanılmış ve sonuçlar tartışılmıştır.

Puls laser depozisyon (PLD) tekniği, ince film ve çok tabakalı yapılar üretmek için oldukça basit ve çok yönlü-esnek bir sistemdir. PLD sistemi kullanılarak, malzeme yapay olarak ince bir tabaka haline getirilmektedir. İnce tabaka haline getirilen malzemenin özellikleri tabaka kalınlıklarına bağlı olarak değişmektedir. İnce film üretiminde, ablasyonla elde edilen demetin özellikleri, film yapısı ve mekanik özellikleri arasındaki ilişki oldukça önemlidir. PLD tekniği kullanılarak ince film üretiminde, ince film özelliklerinin laser güç yoğunluğu, dalgaboyu, numune ve alt tabaka sıcaklıkları ve sistem geometrisine oldukça bağlı olduğu çok iyi bilinmektedir. Oldukça üstün özlellikleri nedeniyle PLD tekniği ince film üretiminde oldukça yaygın bir şekilde kullanılmaktadır. PLD, özellikle erime ve buharlaşma noktası çok yüksek olan, ısıl yöntemlerle buharlaştırılması çok zor olan metalik malzemelerin buharlaştırılmasında etkin bir şekilde kullanılmaktadır. Bor, renyum, tantalyum, titanyum gibi erime ve buharlaşma noktaları çok yüksek olan malzemelerin bu metodla işlenmesi oldukça üstün özellikler ortaya koymaktadır. Bu çerçevede aşırı sert ince tabakaların üretimi oldukça önem kazanmaktadır. Bu nedenle bu tür malzemelerin PLD yöntemi ile işlenmesi, özellikle Puls Laser Ablasyon ve Depozisyon (PLAD) yöntemi ile ince film üretiminde oldukça başarılı sonuçlar vermektedir. Bu çalışmada, grubumuz tarafından üretilem PLD sisteminin detayları ile tanıtılmasının yanı sıra elde edilen bazı önemli sonuçları ortaya konacaktır.

Human vocal folds (VFs) possess a unique anatomical structure and mechanical properties for human communication. However, VFs are prone to scarring as a consequence of overuse, injury, disease or surgery. Accumulation of scar tissue on VFs inhibits proper phonation and leads to partial or complete loss of voice, with significant consequences for the patient's quality of life. VF regeneration after scarring provides a significant challenge for tissue engineering therapies given the complexity of tissue microarchitecture. To establish an effective animal model for VF injury and scarring, new histological methods are required to visualize the wound repair process of the tissue in its three-dimensional native environment. In this work, we propose the use of a combination of nonlinear microscopy and nanotomography as contrast methods for virtual histology of rabbit VFs. We apply these methods to rabbit VF tissue to demonstrate their use as alternatives to conventional VF histology that may enable future clinical studies of this injury model.

We present a review of theoretical and experimental aspects of multiphoton quantum optics. Multiphoton processes occur and are important for many aspects of matter-radiation interactions that include the efficient ionization of atoms and molecules, and, more generally, atomic transition mechanisms; system-environment couplings and dissipative quantum dynamics; laser physics, optical parametric processes, and interferometry. A single review cannot account for all aspects of such an enormously vast subject. Here we choose to concentrate our attention on parametric processes in nonlinear media, with special emphasis on the engineering of nonclassical states of photons and atoms that are relevant for the conceptual investigations as well as for the practical applications of forefront aspects of modern quantum mechanics. We present a detailed analysis of the methods and techniques for the production of genuinely quantum multiphoton processes in nonlinear media, and the corresponding models of multiphoton effective interactions. We review existing proposals for the classification, engineering, and manipulation of nonclassical states, including Fock states, macroscopic superposition states, and multiphoton generalized coherent states. We introduce and discuss the structure of canonical multiphoton quantum optics and the associated one-and two-mode canonical multiphoton squeezed states. This framework provides a consistent multiphoton generalization of two-photon quantum optics and a consistent Hamiltonian description of multiphoton processes associated to higher-order nonlinearities. Finally, we discuss very recent advances that by combining linear and nonlinear optical devices allow to realize multiphoton entangled states of the electromnagnetic field, either in discrete or in continuous variables, that are relevant for applications to efficient quantum computation, quantum teleportation, and related problems in quantum communication and information.

Direct D atom desorption, as well as associative desorption of D2 molecules are observed in thermal desorption from D atoms chemisorbed on a C(0001) surface by combining laser induced T-jumps with resonance enhanced multiphoton ionization detection. Bleaching curves suggest that different classes of chemisorbed D atom clusters are present on the initial surface. The energy resolved atomic desorption flux, obtained via time of flight techniques, compares favorably (via detailed balance) with theoretical calculations of atomic sticking. Density functional theory calculations of chemical processes (atomic desorption, atomic diffusion/cluster annealing, and associative desorption) on an extensive set of four atom H(D) clusters chemisorbed on C(0001) provide a good interpretation of the experiments. State and energy resolved D2 desorption fluxes are compared with previous state averaged results. In combination with density functional theory calculations these measurements reveal a substa...

Using high-intensity femtosecond pulses at λ=264 nm, we have measured the two-photon absorption (TPA) coefficient in three fused silica samples Suprasil, Herasil, Infrasil (Heraeus) and in 3.5 mol % Ge-doped fused silica. While in fused silica samples the TPA coefficient value is about 2×10−11 cm/W, in germanosilicate glass it equals (42±3)×10−11 cm/W.

We present an extensive analysis of one-and two-photon absorption processes in some organic hostguest (H-G) complexes using linear and quadratic response theory within the framework of timedependent density functional theory. For this purpose, we have considered all possible 20 host-guest complexes constructed from 4 host and 5 guest molecules. We have analysed how the one-and two-photon activity of the host and guest molecules are transferred to the respective host-guest complexes and how the electron donating and electron accepting ability of host-guest complexes affect their two-photon activity. Based on an analysis using the concept of channel interference, we have performed an in-depth analysis of the two-photon absorption processes in all these systems and provided a microscopic explanation for their variation among different complexes.

We compare a nonlinear upconversion detector with a conventional cryogenic InSb detector for the detection of coherent infrared light showing near-shot-noise-limited performance in the upconversion system. The InSb detector is limited by dark noise, which results in a 500 times lower signal-to-noise ratio. The two detectors are compared for the detection of a coherent degenerate four-wave mixing (DFWM) signal in the mid-infrared, and applied to measure trace-level acetylene in a gas flow at atmospheric pressure, probing its fundamental rovibrational transitions. In addition to lower noise, the upconversion system provides image information of the signal, thus adding new functionality compared to standard point detection methods. We further show that the upconversion detector system can be implemented as a simple replacement of the cryogenic detector.

Light in the mid-infrared (MIR) has a higher transmission through certain media, such as fog and smoke [1], than visible/near-infrared due to the lower scattering probability. Therefore it is of interest to have LIDARs operating in this spectral region, specifically utilizing photon counting, which yields high sensitivity. However, most photon counting LIDAR systems operate in the near infrared [2-4]. This is due to a lack of good detectors in the MIR. By up-converting the MIR photons to the working regime of established Si-detectors, it is possible to reap the benefits from both the MIR and good detectors. This technique has previously successfully demonstrated detection of MIR both through a single pass configuration [5] or when the nonlinear crystal was inside a laser cavity [6]. This experiment was performed to extend the wavelength of the up-conversion MIR LIDAR to 2.4 µm and achieve high spatial resolution compared to previous up-conversion photon counting LIDARs [7,8]. In this work the nonlinear up-conversion was done inside a Nd:YVO4 cavity lasing at 1064 nm generating light at 737 nm. The LIDAR was performed with the time of flight technique. To do this there were three main components of the setup, the MIR pulses, the conversion cavity and the detector for the up-converted light. The MIR pulses were reflected off a microscope slide, up-converted in the conversion cavity, spectrally filtered and detected. The MIR pulses had a temporal width below 100 fs with a spectral bandwidth of roughly 300 nm centered around 2.4 µm with a repetition rate of 1 kHz and pulse energy in the pJ regime. A 10 mm long (9 mm grating length) periodically-poled rubidium-doped KTiOPO4 (PPRKTP) with a 23.5 µm period was fabricated in-house and used for the up-conversion. The crystal was inserted into a straight Nd:YVO4 laser cavity pumped by a 2.5 W 808 nm laser diode. The PPRKTP crystal was uncoated which resulted in a relatively low intra-cavity power of 5 W at 1064 nm. A conventional silicon single-photon avalanche photodiode (Si-SPAD) with a detection efficiency of 23 % at 737 nm was used in combination with a time tagging unit with bin widths down to 4 ps.

Ultrafast pulsed lasers can be used to achieve remarkable precision during surgical ablation. Through nonlinear interactions with tissue, ultrafast lasers can provide a largely non-thermal mechanism of ablation and a unique ability to create targeted damage within bulk tissue. These advantages have made ultrafast lasers the ideal surgical tool for various novel applications in ophthalmology. Clinical adoption of ultrafast lasers in other surgical applications remains limited in part due to the lack of a means for fiber delivery of ultrafast laser pulses as a flexible, hand-held surgical endoscope. This review provides an overview of the recent advances in bringing this unique surgical tool into the clinic. We discuss fundamental mechanisms and limitations of ultrafast laser ablation, novel techniques for overcoming these limitations, the current state of clinical applications, and conclude with our recent efforts in developing fiber-coupled probes for flexible ultrafast laser surgery and imaging.

Bu çalışmada, yüksek güçlü femtosaniye laserle birlikte TOF-MS kullanılarak C n topak moleküllerinin ve özellikle C 60 fullerene molekülünün üretimi ortaya konmaktadır. Buna ilave olarak kütle spektrumundaki pik deseninin laser gücüne bağlılığı ortaya konmaktadır. Kütle spektrumunda C 60 molekülünün fragmentasyon desenindeki C n + , (n=1….24) iyonlarının ve ana iyonun elde edilmesi çalışılmıştır. Bu tür iyonlaştırma sürecinde dalgaboyuna ve laser gücüne bağlı olarak femtosaniye kısa laser pulsları kullanılarak moleküler iyon elde edilebilmektedir. Aynı zamanda hedef olarak grafit kullanılmak suretiyle C n + (n=1…60) karbon topaklarının birleşme yoluyla elde edilmesine çalışılmış ve elde edilen spektrum analiz edilmiştir. %99,5 saflıkta C 60 molekülünün ve grafitin bir hedef numune olarak kullanıldığı bu çalışmada, düşük laser yoğunluklarında alınan kütle spektrumunda çok küçük bir ana iyon gözlenmiştir. Bu çalışmada, 800 nm dalga boyu için yaklaşık olarak 10 12-14 W/cm 2 laser yoğunlukları kullanılmış ve sonuçlar tartışılmıştır.

OBJETIVO: O objetivo deste trabalho é o de verificar a aplicabilidade do método imunohistoquímico na quantificação das diferentes formas das fibras elásticas em prega vocal humana. FORMA DE ESTUDO: coorte transversal. MATERIAL E MÉTODO: Foram seguidos os seguintes critérios de inclusão: idade entre 25 e 40 anos, gênero masculino, cor branca, morte causada por ferimento de arma de fogo, menos de doze horas de morte, ausência de intubação traqueal e de trauma na região cervical e que, por análise microscópica, não apresentassem qualquer alteração da mucosa das pregas vocais. Por estes critérios dez pregas vocais foram obtidas e selecionou-se, aleatoriamente, uma prega vocal que pertencia a um indivíduo de 28 anos. A prega vocal foi transversalmente seccionada em nove regiões e três cortes de cada fragmento foram utilizados para a realização das colorações Verhoeff e resorcina-fuchsina de Weighert e para a realização do estudo imunohistoquímico. Realizou-se quantificação colorimétrica ...

Diamond's nitrogen-vacancy (NV) centers show great promise in sensing applications and quantum computing due to their long electron spin coherence time and their ability to be located, manipulated and read out using light. The electrons of the NV center, largely localized at the vacancy site, combine to form a spin triplet, which can be polarized with 532-nm laser light, even at room temperature. The NV's states are isolated from environmental perturbations making their spin coherence comparable to trapped ions. An important breakthrough would be in connecting, using waveguides, multiple diamond NVs together optically. However, the inertness of diamond is a significant hurdle for the fabrication of integrated optics similar to those that revolutionized silicon photonics. In this work we show the possibility of buried waveguide fabrication in diamond, enabled by focused femtosecond high repetition rate laser pulses. We use µRaman spectroscopy to gain better insight into the structure and refractive index profile of the optical waveguides.

We investigate theoretically how single-molecule spectroscopy techniques can be used to perform fast and high resolution displacement detection and manipulation of nanomechanical oscillators, such as singly clamped carbon nanotubes. We analyze the possibility of real time displacement detection by the luminescence signal and of displacement fluctuations by the degree of second order coherence. Estimates of the electro-mechanical coupling constant indicate that intriguing regimes of strong back-action between the two-level system of a molecule and the oscillator can be realized.

We demonstrate a photon-sensitive, three-dimensional (3D) camera by active near-infrared illumination and fast time-of-flight gating. It uses picosecond pump pulses to selectively upconvert the backscattered photons according to their spatiotemporal modes via sum-frequency generation in a χ 2 nonlinear crystal, which are then detected by an electron-multiplying CCD with photon sensitive detection. As such, it achieves sub-millimeter depth resolution, exceptional noise suppression, and high detection sensitivity. Our results show that it can accurately reconstruct the surface profiles of occluded targets placed behind highly scattering and lossy obscurants of 14 optical depth (round trip), using only milliwatt illumination power. This technique may find applications in biomedical imaging, environmental monitoring, and wide-field light detection and ranging.

High-dimensional (dimension d > 2) quantum key distribution (QKD) protocols that encode information in the temporal degree of freedom promise to overcome some of the challenges of qubit-based (d = 2) QKD systems. In particular, the long recovery time of single-photon detectors and large channel noise at long distance both limit the rate at which a final secure key can be generated in a low-dimension QKD system. We propose and demonstrate a practical discrete-variable time-frequency protocol with d = 4 at a wavelength of 1550 nm, where the temporal states are secured by transmitting and detecting their dual states under Fourier transformation, known as the frequency-basis states, augmented by a decoy-state protocol. We show that the discrete temporal and frequency states can be generated and detected using commercially-available equipment with high timing and spectral efficiency. In our initial experiments, we only have access to detectors that have low efficiency (1%) at 1550 nm. Together with other component losses, our system is equivalent to a QKD system with ideal components and a 50-km-long optical-fiber quantum channel. We find that our system maintains a spectral visibility of over 99.0% with a quantum bit error rate of 2.3%, which is largely due to the finite extinction ratio of the intensity modulators used in the transmitter. The estimated secure key rate of this system is 7.7×10 4 KHz, which should improve drastically when we use detectors optimized for 1550 nm.

We have investigated multiple ionization of N 2 and O 2 molecules by 52 nm extreme-ultraviolet light pulses at the free-electron laser facility SCSS in Japan. Coulomb break-up of parent ions with charge states up to 5+ is found by the ion-ion coincidence technique. The charge-state dependence of kinetic energy release distributions suggests that the electrons are emitted sequentially in competition with the elongation of the bond length.

A Ti:sapphire based chirped-pulse amplification system provides ultrashort laser pulses (~25 fs, 1.2 mJ, central wavelength 796 nm) at 1 kHz repetition rate. These pulses are compressed to 7-12 fs by filament compression [1] in two Ar gas cells. The beam is then split into a probe branch (20%) that is sent through a delay line and a pump branch (80%), which produces attosecond pulse trains (20-45 eV, 300 as pulse width) by high-harmonic generation in Ar. After generation of the APT the residual IR and lower-order harmonic radiation is blocked by a 100 nm Al filter. Pump and probe beams are collinearly recombined by means of a drilled mirror; the harmonic radiation passes from behind through the centre hole (diameter 2 mm) of the mirror while the IR probe field is reflected on the front part. A gold-coated toroidal mirror (incidence angle 82°) focuses the two beams in front of a time-of-flight (ToF) spectrometer. Photoemission spectra from Ar gas are recorded at different delays between the two pulses (typical delay step = 250 as). The collection of these spectra constitutes the first RABBITT trace that was used for calibration purpose. A second toroidal mirror (incidence angle 80°) images the first focus onto a solid sample surface in a one-to-one geometry. Photoemission spectra from the metal surface are recorded with a hemispherical electron analyser. These spectra are measured simultaneously with the ones in Ar and form the second RABBITT trace. Efficient differential pumping kept the pressure in the surface chamber below 7×10-10 mbar during the measurements, which allowed for prolonged acquisition without degradation of the surface by contamination. Ag(111) and Au(111) single crystals were cleaned by cycles of sputtering and annealing and the surface quality was verified by XPS and LEED. The propagation phase between the two foci was determined experimentally by performing a simultaneous RABBITT experiment with two Ar targets. All measurements were conducted at room temperature and a bias voltage of-5.00 V with respect to the analyzer was applied to the solid sample. The intensity settings for the simultaneous scans were optimized for the surface with a focus on clear SB contrast. Reasonable modulation contrast in the SB signal was obtained with an incidence angle of 75°. All data presented in this work were recorded at this incidence angle. Both pulses are p-polarized and the angle of incidence on the surface is 75°.

The matrix elements of two-photon direct optical transitions between the valence and conduction bands in narrow-gap semiconductors in the three-band Kane model were calculated. All types of optical transitions were analyzed, which differ from the initial states of current carriers, leading to linear-circular dichroism in narrow-gap semiconductors with taking into account the effect of coherent saturation in two-photon optical transitions.

Important aspects of the passive mechanical properties of skeletal muscle tissue are not yet fully understood. The prediction of passive tissue response to mechanical stimulation is relevant to numerous fields of engineering and research. This study aims to investigate the extracellular matrix contribution on a microscopic scale. Here, a novel micro-force sensor technology is applied to the testing of biological materials and is shown to reliably recognize the anisotropy of the fibrous muscular tissue in small samples. The preparation of even smaller tissue samples with microscopic dimensions by femtosecond-laser ablation has been studied with respect to laser parameters and their influence on thermal damage in the tissue and structure-fidelity. The ablation strategy has been found to have an impact on tissue degeneration. A suitable pulse energy range has been identified for the chosen ablation strategy.

Using high-intensity femtosecond pulses at ϭ264 nm, we have measured the two-photon absorption ͑TPA͒ coefficient in three fused silica samples Suprasil, Herasil, Infrasil ͑Heraeus͒ and in 3.5 mol % Ge-doped fused silica. While in fused silica samples the TPA coefficient value is about 2ϫ10 Ϫ11 cm/W, in germanosilicate glass it equals (42Ϯ3)ϫ10 Ϫ11 cm/W.

Spherical domes are created on the surface of polycarbonate samples, and microvoids are formed within the bulk using only a femtosecond oscillator with pulse energy of just 0.47 nJ. Size of spherical domes and shape of microvoids are controlled by changing the laser focus inside the material. Their formation is explained by a combination of heat accumulation and dome formation dynamics, where the dome acts as a microlens shifting the laser focus within the sample. The technique described here provides a simple avenue for fabricating smooth microlens arrays of various sizes and opens the possibility for direct fabrication of complex three-dimensional microfluidic channels in transparent materials.

Towards developing a new method for restoring tissue viscoelasticity in scarred vocal folds, we previously proposed to localize biomaterials within sub-epithelial voids ablated using ultrafast laser pulses. The clinical implementation of this method necessitates the quantification of the laser parameters for ablating scarred tissue. Here, we present a comprehensive study of these parameters including ablation threshold and bubble lifetime in healthy and scarred tissues. We also present a new method for extracting tissue-specific ablation threshold and scattering lengths of different tissue layers. This method involves finding the ablation threshold at multiple depths and solving the equations based on Beer's Law of light attenuation for each depth to estimate the unknown parameters. Measured threshold fluences were 1.75 J/cm 2 for vocal folds and 0.5 J/cm 2 for cheek pouches for 3-ps, 776-nm laser pulses. Scarred pouches exhibited 30% lower threshold than healthy pouches, possibly due to the degraded mechanical properties of scarred collagen during wound healing. The analysis of tissue architecture indicated a direct correlation between the ablation threshold and tissue tensile strength and that the bubble lifetime is inversely related to tissue stiffness. Overall, this study sheds light on the required laser parameters for successful implementation of ultrafast laser ablation for phonosurgery.

Multiphoton microscopes become important tools for noncontact sub-wavelength three-dimensional nanoprocessing of living biological specimens based on multiphoton ionization and plasma formation. Ultrashort laser pulses are required, however, dispersive effects limit the shortest pulse duration achievable at the focal plane. We report on a compact nonlinear laser scanning microscope with sub-20 femtosecond 75 MHz near infrared laser pulses for nanosurgery of human stem cells and two-photon high-resolution imaging. Single point illumination of the cell membrane was performed to induce a transient nanopore for the delivery of extracellular green fluorescent protein plasmids. Mean powers of less than 7 mW (<93 pJ) and low millisecond exposure times were sufficient to transfect human pancreatic and salivary gland stem cells. Ultracompact sub-20 femtosecond laser microscopes may become optical tools for nanobiotechnology and nanomedicine including optical stem cell manipulation.

We present the results of our investigations of the dynamics of a classical hydrogen atom submitted to an intense classical radiation field with a relatively low frequency as compared to the characteristic Kepler frequency of the atomic system. We discuss here the harmonic spectra which can be deduced from a Fourier analysis of the time evolution of the strongly driven atomic dipole, associated either with a single trajectory or with ensembles of trajectories evolving from an initial microcanonical distribution. The spectra obtained from ensemble-averaged atomic dipoles qualitatively reproduce the main features of those recently observed in experiments and allow, in particular, discussion of the occurrence of a plateau in the distribution of harmonic intensities as a function of their order. The possible competition between harmonic generation and multiphoton ionization, which both take place in the same laserintensity range, is also discussed.

We propose a method to study and characterize the spatial and temporal properties of degenerate photon pairs emitted in SPDC, using a filtering system combined with temperature variation of the nonlinear crystal. The photons can be distinguished. We relate these to the measured Hong-Ou-Mandel interference dip of the photons, measured in a parallel experiment. The theoretical plots match very well with the experimental results.

Objectives/Hypothesis: High-frequency ultrasound imaging offers the potential for assisting in the diagnosis and treatment of vocal fold pathology if it allows aspects of vocal fold microstructure to be visualized noninvasively. The objective of this study was to assess the ability of high-frequency ultrasound to image vocal fold anatomy and injected biomaterials. Study Design: The vocal folds of two excised calf larynges were imaged ex vivo and compared with corresponding histological sections. Methods: High-frequency ultrasound imaging was performed under saline submersion using 40 and 50 MHz transducers, and corresponding cryostat cross-sections were stained with H&E, Trichome, and Verhoeff's Van Gieson stains. Results: The epithelial surface, lamina propria, and underlying muscle were easily identified with the highfrequency ultrasound as verified with histological sections representing each imaged region. The arytenoid cartilage vocal process can also be clearly distinguished from the surrounding tissue, as can the full extent of injected biomaterials within the superficial lamina propria. Useful ultrasound resolution was obtained to depths of at least 10 mm within the tissue with the 40 MHz transducer. Conclusions: This preliminary study demonstrates the capability of high-frequency ultrasound to image the layered anatomy of the calf vocal fold and to discern materials injected into the superficial lamina propria, indicating that this technology holds a strong potential for use in phonosurgery.

We describe precise optical attenuation measurements of LAB based liquid scintillators using a custombuilt photometer with variable pathlengths up to 2 m. Results are presented for linear alkyl benzene (LAB) and LAB based liquid scintillators at wave lengths of 405, 430, 450, and 470 nm. For these measurements much care was exercised to control the purity of the liquids and additives, as well as the materials of the photometer to control contaminations. These data should be valuable for design of large detectors, such as underground neutrino detectors, using these materials as the media.

The focusing of multimode laser diode beams is probably the most significant problem that hinders the expansion of the high-power semiconductor lasers in many spatially-demanding applications. Generally, the 'quality' of laser beams is characterized by so-called 'beam propagation parameter' M 2 , which is defined as the ratio of the divergence of the laser beam to that of a diffraction-limited counterpart. Therefore, M 2 determines the ratio of the beam focal-spot size to that of the 'ideal' Gaussian beam focused by the same optical system. Typically, M 2 takes the value of 20-50 for high-power broad-stripe laser diodes thus making the focal-spot 1-2 orders of magnitude larger than the diffraction limit. The idea of 'superfocusing' for high-M 2 beams relies on a technique developed for the generation of Bessel beams from laser diodes using a cone-shaped lens (axicon). With traditional focusing of multimode radiation, different curvatures of the wavefronts of the various constituent modes lead to a shift of their focal points along the optical axis that in turn implies larger focal-spot sizes with correspondingly increased values of M 2. In contrast, the generation of a Bessel-type beam with an axicon relies on 'self-interference' of each mode thus eliminating the underlying reason for an increase in the focal-spot size. For an experimental demonstration of the proposed technique, we used a fiber-coupled laser diode with M 2 below 20 and an emission wavelength in ~1μm range. Utilization of the axicons with apex angle of 140deg, made by direct laser writing on a fiber tip, enabled the demonstration of an order of magnitude decrease of the focal-spot size compared to that achievable using an 'ideal' lens of unity numerical aperture.

Bu çalışmada, yüksek güçlü femtosaniye laserle birlikte TOF-MS kullanılarak C n topak moleküllerinin ve özellikle C 60 fullerene molekülünün üretimi ortaya konmaktadır. Buna ilave olarak kütle spektrumundaki pik deseninin laser gücüne bağlılığı ortaya konmaktadır. Kütle spektrumunda C 60 molekülünün fragmentasyon desenindeki C n + , (n=1….24) iyonlarının ve ana iyonun elde edilmesi çalışılmıştır. Bu tür iyonlaştırma sürecinde dalgaboyuna ve laser gücüne bağlı olarak femtosaniye kısa laser pulsları kullanılarak moleküler iyon elde edilebilmektedir. Aynı zamanda hedef olarak grafit kullanılmak suretiyle C n + (n=1…60) karbon topaklarının birleşme yoluyla elde edilmesine çalışılmış ve elde edilen spektrum analiz edilmiştir. %99,5 saflıkta C 60 molekülünün ve grafitin bir hedef numune olarak kullanıldığı bu çalışmada, düşük laser yoğunluklarında alınan kütle spektrumunda çok küçük bir ana iyon gözlenmiştir. Bu çalışmada, 800 nm dalga boyu için yaklaşık olarak 10 12-14 W/cm 2 laser yoğunlukları kullanılmış ve sonuçlar tartışılmıştır.