Optical Rectification

We demonstrate the generation of single-cycle 0.1-THz radiation in a lithium niobate crystal using optical rectification and obtain THz output energy of 65 µJ with 31.6 MV/m peak field. This amounts to an optical-to-THz energy conversion efficiency of 0.3% at 85 K, which is in agreement with theory.

We demonstrate the generation of 100 GHz single-cycle pulses with up to 10 MW of peak power using optical rectification and broadband phase matching via the tilted pulse front (TPF) technique in lithium niobate. The optical driver is a cryogenically cooled Yb:YAG amplifier providing tens of mJ energy, ~5 ps long laser pulses. We obtain a high THz pulse energy up to 65 µJ with 31.6 MV/m peak electric field when focused close to its diffraction limit of 2.5 mm diameter. A high optical-to-THz energy conversion efficiency of 0.3% at 85 K is measured in agreement with numerical simulations. This source is of great interest for a broad range of applications, such as nonlinear THz field-matter interaction and charged particle acceleration for ultrafast electron diffraction and table-top X-ray sources.

We demonstrate highly efficient THz generation by optical rectification of near optimum pump pulses centered at 1.03 m in cryogenically cooled lithium niobate. Using a close to optimal pulse duration of 680 fs and a pump energy of 1.2 mJ, we report conversion efficiencies above 3.8±0.4%, which is more than an order-of-magnitude higher than previously reported. The results confirm the advantage of using cryogenic cooling of the lithium niobate crystal that significantly reduces the THz absorption, enabling the scaling of THz pulse energies to the mJ level via optical rectification.

A model for THz generation by optical rectification using tiltedpulse-fronts is developed. It simultaneously accounts for (i) the spatio-temporal distortions of the optical pump pulse, (ii) the nonlinear coupled interaction of THz and optical radiation in two spatial dimensions (2-D), (iii) self-phase modulation and (iv) stimulated Raman scattering. The model is validated by quantitative agreement with experiments and analytic calculations. We show that the optical pump beam is significantly broadened in the transversemomentum (k x ) domain as a consequence of the spectral broadening caused by THz generation. In the presence of this large frequency and transversemomentum (or angular) spread, group velocity dispersion causes a spatiotemporal break-up of the optical pump pulse which inhibits further THz generation. The implications of these effects on energy scaling and optimization of optical-to-THz conversion efficiency are discussed. This suggests the use of optical pump pulses with elliptical beam profiles for large optical pump energies. It is seen that optimization of the setup is highly dependent on optical pump conditions. Trade-offs of optimizing the optical-to-THz conversion efficiency on the spatial and spectral properties of THz radiation is discussed to guide the development of such sources.

Terahertz (THz) waves, known as non-ionizing radiation owing to their low photon energies, can actually ionize atoms and molecules when a sufficiently large number of THz photons are concentrated in time and space. Here, we demonstrate the generation of ionizing, multicycle, 15-THz waves emitted from large-area lithium niobate crystals via phase-matched optical rectification of 150-terawatt laser pulses. A complete characterization of the generated THz waves in energy, pulse duration, and focal spot size shows that the field strength can reach up to 260 megavolts per centimeter. In particular, a single-shot THz interferometer is employed to measure the THz pulse duration and spectrum with complementary numerical simulations. Such intense THz pulses are irradiated onto various solid targets to demonstrate THz-induced tunneling ionization and plasma formation. This study also discusses the potential of nonperturbative THz-driven ionization in gases, which will open up new opportunitie...

Pulsed terahertz (THz) radiation, generated through optical rectification (OR) by exciting 〈110〉 ZnTe crystal with ultrafast optical pulses, typically consists of only a few-cycles of electromagnetic field oscillations with a duration about a couple of picoseconds. However, it is possible, under appropriate conditions, to generate a long damped oscillation tail (LDOT) following the main cycles. The LDOT can last tens of picoseconds and its Fourier transform shows a higher and narrower frequency peak than that of the main pulse. We have demonstrated that the generation of the LDOT depends on both the duration of the optical pulse and its central wavelength. Furthermore, we have also performed theoretical calculations based upon the OR effect coupled with the phonon-polariton mode of ZnTe and obtained theoretical THz waveforms in good agreement with our experimental observation.

In this study, the effects of a non-resonant intense laser field and the Al-concentration on the optical rectification, second and third harmonic generation in asymmetric double quantum well are investigated within the compact density matrix approach theoretically. The results show that the intense laser field and the Al-concentration lead to significant changes in the coefficients of nonlinear optical rectification, second and third harmonic generations.

The sub-luminal phase velocity of electromagnetic waves in free space is generally unobtainable, being closely linked to forbidden faster than light group velocities. The requirement of sub-luminal phase-velocity in laser-driven particle acceleration schemes imposes a limit on the total acceleration achievable in free space, and necessitates the use of dispersive structures or waveguides for extending the field-particle interaction. We demonstrate a travelling source approach that overcomes the sub-luminal propagation limits. The approach exploits ultrafast optical sources with slow group velocity propagation, and a group-to-phase front conversion through nonlinear optical interaction. The concept is demonstrated with two terahertz generation processes, nonlinear optical rectification and current-surge rectification. We report measurements of longitudinally polarised single-cycle electric fields with phase and group velocity between 0.77c and 1.75c. The ability to scale to multi-meg...

A new scheme for generating high-energy terahertz (THz) pulses based on using a multistep phase mask (MSPM) is suggested and analyzed. The mask is placed on the entrance surface of the nonlinear optical (NLO) crystal eliminating the necessity of the imaging optics. In contrast to the contact grating method, introduction of large amounts of angular dispersion is avoided. The operation principle of the suggested scheme is based on the fact that the MSPM splits a single input beam into many smaller time-delayed Bbeamlets,^which together form a discretely tilted-front laser pulse in NLO crystal. The analysis of THz-pulse generation in ZnTe and lithium niobate (LN) crystals shows that application of ZnTe crystal is more preferable, especially when long-wavelength pump sources are used. The dimensions of the mask's steps required for high-energy THz-pulse generation in ZnTe and LN crystals are calculated. The optimal number of steps is estimated, taking into account individual beamlet's spatial broadening and problems related to the mask fabrication. The proposed method is a promising way to develop high-energy, monolithic, and alignment-free THz-pulse sources.

We propose and experimentally demonstrate the generation of single-cycle terahertz radiation with two-stage optical rectification in GaSe crystals. By adjusting the time delay between the pump pulses employed to excite the two stages, the terahertz radiation from the second GaSe crystal can constructively superpose with the terahertz field injected from the first stage. The high mutual coherence between the two terahertz radiation fields is ensured with the coherent optical rectification process and can be further used to synthesize a desired spectral profile of coherent THz radiation. The technique is also potentially useful for generating high-power single-cycle terahertz pulses, usually limited by the pulse walk-off effect of the nonlinear optical crystal used.

We demonstrated fast three-dimensional transmission terahertz computed tomography by using real-time line projection of intense terahertz beam generated by optical rectification in lithium niobate crystal. After emphasizing the advantage of intense terahertz pulse generation for twodimensional spatio-temporal terahertz imaging, peak-to-peak amplitudes of pulsed terahertz electric field have been used to obtain a series of projection images at different rotation angles. Then a standard reconstruction algorithm has been employed to perform final three-dimensional reconstruction. Test samples including a medicine capsule have been investigated with a total acquisition time to only 6 minutes.

Near single-cycle terahertz pulse generation from lithium niobate crystal by optical rectification of pulses from an Yb:fiber laser/amplifier system was investigated. The pump laser supplied 250 fs duration pulses with 14 μJ energy at up to 1 MHz repetition rate. The terahertz pulse energy and average power exceeded 0.25 nJ and 0.25 mW, respectively. The average power was more than ten times higher than corresponding values achieved by using GaP as the nonlinear crystal under similar pumping conditions.

We record a sub-wavelength terahertz image of a caster sugar grain thanks to optical rectification in the sample excited with a femtosecond laser beam. The lateral spatial resolution of this technique is given by the laser spot size at the sample and here its measured value is 50 μm, i.e. ~λ/12. We give an estimation of the ultimate resolution that could be achieved with this method.

In this paper, we give an overview of emission and detection of terahertz electromagnetic pulses using, respectively, optical rectification and electro-optic effect in [111] zinc blende crystals. This crystal orientation allows us to generate and read any polarization state of the THz beam only by controlling the polarization state of the laser beam that excites or probes the emitting and receiving crystals. This technique is very useful for polarimetric terahertz spectroscopic studies.

We have performed calculations of nonlinear optical absorption and nonlinear optical rectification of an exciton in a nanoring in the presence of the magnetic flux. Our results show that one can control properties of nonlinear optical absorption and nonlinear optical rectification of a nanoring by tuning outer and inner radius. In addition, we also find that nonlinear optical properties of a nanoring can be modulated by the magnetic flux through nanoring.

An analytical expression has been derived for terahertz (THz) emission by optical rectification of a laser pulse having a Gaussian as well as hyperbolic-secant shape in axially magnetised ripple density plasma. The interaction between short laser pulses of sub picoseconds duration and plasma leads to the radiation of a wave having frequency in THz regime. The non-uniform intensity profile, say supper-Gaussian, of laser beam exerts a quasi-static ponderomotive force to the electron. The electron acquired a nonlinear transverse drift velocity component. Hence, a strong transient current density having a frequency component in the THz regime produces due to coupling of this velocity component with ripple density plasma and derives a strong THz wave. The generated THz field amplitude is directly proportional to the amplitude of the density ripple and field amplitude of the laser beam. In this generation mechanism, the ripple wave number plays a critical role. The THz field amplitude is ...

In this comment, we review the work by Xie [Phys. Status Solidi B 246, 2257] on electric field effects and nonlinear optical properties of excitons confined in spherical quantum dots. We find an inconsistency in the calculation of the dipole moments, which lead to vanishing nonlinear optical results. For the same set of parameters studied by Xie, we obtain new and reliable optical rectification coefficients via a finite element approach.

We have measured the rectification of far-infrared ~dlation resonant with the lowest intersubband transition of an AIGaAs/GaAs asymmetric coupled double-quantum well in which the subband spacing is 11 meV. From these measurements we can extract an intersubband lifetime of 1.2 +0.4 ms at low excitation intensity and T--10 K, which appears promising for devices which can operate at low excitation and temperature, such as FIR detectors or mixers. From simultaneous measurements of the optical rectification and of the intersubband absorption coefficient we can determine the intensity-dependent intersubband lifetime, which shows a strong decrease for increasing inteusitim.

We report measurements of the rectification of microwave radiation (0.7-20 GHz) at the boundary between two-dimensional electron systems separated by a narrow gap on a silicon surface for different temperatures, electron densities and microwave power. For frequencies above 4 GHz and different temperatures, the rectified voltage V dc as a function of microwave power P can be scaled onto a single universal curve V * dc = f * (P *). The scaled voltage is a linear function of power, V * dc ∝ P * for small power and proportional to (P *) 1/2 at higher power. A theory is proposed that attributes the rectification to the thermoelectric response due to strong local overheating by the microwave radiation at the boundary between two dissimilar 2D metals. Excellent agreement is obtained between theory and experiment.

The University of Manchester Matthew J. Cliffe Doctor of Philosophy Generation of Longitudinally Polarised Terahertz Radiation for the Energy Manipulation of Relativistic Electron BeamsSeptember 2015The acceleration of charged particles with ultrafast terahertz electromagnetic radiation could enable new, and improve many of aspects of, accelerator applications. These include providing shorter electron bunches for ultrafast time-resolved pump-probe spectroscopy, enabling complex longitudinal profiles to be imparted onto charged particle bunches and significantly improving the ability to synchronise an accelerator to an external laser. In this thesis I present investigations into terahertz radiation sources that enabled the generation of terahertz radiation with attractive properties for accelerator based applications. Specific attention has been paid to temporally tunable sources that generate strong longitudinally polarised electric field components as these enable a free-space co-l...

In this work the effects of intense laser on the electron-related nonlinear optical absorption and nonlinear optical rectification in GaAs-Ga 1−x Al x As quantum wells are studied under, applied electric and magnetic field. The electric field is applied along the growth direction of the quantum well whereas the magnetic field has been considered to be in-plane. The calculations were performed within the density matrix formalism with the use of the effective mass and parabolic band approximations. The intense laser effects are included through the Floquet method, by modifying the confining potential associated to the heterostructure. Results are presented for the nonlinear optical absorption, the nonlinear optical rectification and the resonant peak of these two optical processes. Several configurations of the dimensions of the quantum well, the applied electric and magnetic fields, and the incident intense laser radiation have been considered. The outcome of the calculation suggests that the nonlinear optical absorption and optical rectification are non-monotonic functions of the dimensions of the heterostructure and of the external perturbations considered in this work.

We report the emission of strong coherent broadband terahertz radiation from 6H-silicon-carbide (SiC) excited with optical pulses. The measured terahertz spectral signal-to-noise ratio is better than one thousand. We determine that the terahertz radiation is generated via second order optical nonlinearity (optical rectification). We present a measurement of the ratio of nonlinear susceptibility tensor elements χzzz(2)/χzxx(2) and the complex index of refraction of silicon carbide at terahertz frequencies.

Two aminopyridinium based novel organic materials, 2-amino-5-nitropyridinium p-phenolsulfonate (2A5NPP) and 2,6-diaminopyridinium-4-nitrophenolate-4-nitrophenol (DAP + NP -NP) were characterized in the 0-2 THz range by time-domain terahertz (THz) spectroscopy. Density functional theory calculations were carried out to find the molecular vibrational modes of the materials in 0-15 THz range and partially compared with the experimental results. THz absorption peaks were assigned to molecular vibration modes. THz pulse generation by optical rectification in both materials was studied using optical pump pulses of 1030 nm wavelength. The anisotropy of THz generation was investigated in detail by rotating the polarization of the optical pump with respect to the crystal axes.

We present a new and viable method for optical rectification. This approach has been demonstrated both theoretically and experimentally and is the basis fot the development of devices to rectify radiation through the visible. This technique for rectification is based not on conventional material or temperature asymmetry as used in MIM (metal/insulator/metal) or Schottky diodes, but on a purely sharp geometric property of the antenna. This sharp “tip” or edge with a collector anode constitutes a tunnel junction. In these devices the rectenna (consisting of the antenna and the tunnel junction) acts as the absorber of the incident radiation and the rectifier. Using current nanofabrication techniques and the selective atomic layer deposition (ALD) process, junctions of 1 nm can be fabricated, which allow for rectification of frequencies up to the blue portion of the spectrum. To assess the viability of our approach, we review the development of nanoantenna structures and tunnel junction...

The process of terahertz generation through optical rectification in a nonlinear crystal is modeled using discretized equivalent current sources. The equivalent terahertz sources are distributed in the active volume and computed based on a separately modeled near-infrared pump beam. This approach can be used to define an appropriate excitation for full-wave electromagnetic numerical simulations of the generated terahertz radiation. This enables predictive modeling of the near-field interactions of the terahertz beam with micro-structured samples, e.g. in a near-field timeresolved microscopy system. The distributed source model is described in detail, and an implementation in a particular full-wave simulation tool is presented. The numerical results are then validated through a series of measurements on square apertures. The general principle can be applied to other nonlinear processes with possible implementation in any full-wave numerical electromagnetic solver.

The exciton binding energy of an asymmetrical GaAs-Ga1−x Al x As cylindrical quantum dot is studied with the use of the effective mass approximation and a variational calculation procedure. The influence on this quantity of the application of a direct-current electric field along the growth direction of the cylinder, together with that of an intense laser field, is particularly considered. The resulting states are used to calculate the exciton-related nonlinear optical absorption and optical rectification, whose corresponding resonant peaks are reported as functions of the external probes, the quantum dot dimensions, and the aluminum molar fraction in the potential barrier regions.

We present experimental results on generation of pulsed terahertz radiation in a ZnTe crystal using nonlinear optical rectification of high-power femtosecond laser pulses. The use of terahertz pulses for spectroscopy is tested in the rotational lines of absorption of water vapors in the atmosphere. Panoramic spectra of absorption of a number of solvents and protein solutions are measured in the range from 0.2 to 2 THz.

We present experimental results on generation of pulsed terahertz radiation in a ZnTe crystal using nonlinear optical rectification of high-power femtosecond laser pulses. The use of terahertz pulses for spectroscopy is tested in the rotational lines of absorption of water vapors in the atmosphere. Panoramic spectra of absorption of a number of solvents and protein solutions are measured in the range from 0.2 to 2 THz.

We have observed far-infrared radiation generated in a LiNb0 3 crystal by picosecond light pulses from a mode-locked Nd: glass laser. The output spectra were analyzed by a Michelson interferometer and a Fabry-Perot interferometer. In one experiment a 0.77 rom thick LiNb0 3 crystal was used to rectify the laser pulses. The resulting spectrum

We studied cascaded optical rectification processes for intense terahertz (THz) pulse generation in electro-optic crystals using simulations based on one-dimensional coupled propagation equations of THz and optical fields. We found that under ideal conditions of perfect phase matching and no absorption, cascaded optical rectification processes produce intense THz pulses with efficiencies exceeding the Manley-Rowe limit. Large red shifting of the pump light spectrum was observed. Effects of finite optical and THz absorption, phase mismatches, and pulse width were examined using parameters of a ZnTe crystal pumped by 800 nm pulses. THz field enhancement by multiple pulse pumping was also studied.

We present an analytical model describing the full electromagnetic propagation in a THz time-domain spectroscopy (THz-TDS) system, from the THz pulses via Optical Rectification to the detection via Electro Optic-Sampling. While several investigations deal singularly with the many elements that constitute a THz-TDS, in our work we pay particular attention to the modelling of the time-frequency behaviour of all the stages which compose the experimental set-up. Therefore, our model considers the following main aspects: (i) pump beam focusing into the generation crystal; (ii) phase-matching inside both the generation and detection crystals; (iii) chromatic dispersion and absorption inside the crystals; (iv) Fabry-Perot effect; (v) diffraction outside, i.e. along the propagation, (vi) focalization and overlapping between THz and probe beams, (vii) electro-optic sampling. In order to validate our model, we report on the comparison between the simulations and the experimental data obtained...

We report on the THz generation and optical characterizations such as index of refraction, absorption coefficients of indigenously grown, potentially NLO active N-benzyl-2-methyl-4nitroaniline (BNA) single crystals grown from four different solvents such as N, N dimethylformamide (DMF), Methanol (MeOH), Acetonitrile (ACN) and ACN: DMF (1:1) in an intentionally selected frequency range of 0.1-2.0 THz at room temperature (RT).The DMF was identified to be a promising candidate as it facilitated reduction in the inclusions. The powder Second Harmonic Generation (SHG) measurements performed on BNA polycrystalline samples revealed that their efficiencies were about 8.4 and 2.3 times higher than KDP and Urea samples respectively. The absorption coefficients and refractive indices made in this technologically important THz range using the BNA crystals grown from selected solvents exhibited, interestingly, solvent dependency.

Interaction of electromagnetic radiation with time-variant objects is a fundamental problem whose study involves foundational principles of classical electrodynamics. Such study is a necessary preliminary step for delineating the novel research field of linear time-varying metamaterials and metasurfaces. A closer look to the literature, however, reveals that this crucial step has not been addressed and important simplifying assumptions have been made. Before proceeding to studies of linear time-varying metamaterials and metasurfaces with their effective parameters, we need to rigorously describe the electric and magnetic responses of a temporally modulated meta-atom. Here, we introduce a theoretical model which describes a time-variant meta-atom and its interaction with incident electromagnetic waves in time domain. The developed general approach is specialized for a dipole emitter/scatterer loaded with a time-varying reactive element. We confirm the validity of the theoretical model with full-wave simulations. Our study is of major significance also in the area of nanophotonics and nano-optics because the optical properties of all-dielectric and plasmonic nanoparticles can be varied in time in order to achieve intriguing scattering phenomena.

We demonstrate the generation of single-cycle 0.1-THz radiation in a lithium niobate crystal using optical rectification and obtain THz output energy of 65 µJ with 31.6 MV/m peak field. This amounts to an optical-to-THz energy conversion efficiency of 0.3% at 85 K, which is in agreement with theory.

Electromagnetic wave emission based on optical rectification at terahertz (THz) wavelengths was observed from surface-immobilized gold nanospheres (SIGNs) above a gold surface. Although the excitation wavelength is offresonant with the localized surface plasmons, the THz emission field was observed to be approximately 4.8 times greater than that from a percolated gold thin film of 10 nm thickness. A theoretical calculation predicts that the light electric field is enhanced in the SIGN system, even at off-resonance wavelengths. The observed THz field amplitude was quadratic with the illumination light field, suggesting that the THz generation is due to a second-order nonlinear optical process.

Following our measurements and analysis made on several GaSe crystals, we demonstrated that terahertz (THz) generation from ultrafast laser pulses can be developed into a sensitive technique for investigating symmetries of second-order nonlinear susceptibility tensor of a nonlinear crystal. Indeed, for GaSe crystals, both Kleinman's symmetry condition and spatial symmetry were violated due to the contribution of ionic displacement to nonlinear polarization and deviation of GaSe lattice from hexagonal symmetry. When the pump photon energy was increased from that below the bandgap of GaSe to that above it, the mechanism for the THz generation was switched from optical rectification to photocurrent surge.

We have investigated the characteristics of THz generation including the dependence of the output power and polarization on the incident angle and pump polarization from two series of InN films grown by plasma-assisted molecular beam epitaxy (PAMBE) and metal organic chemical vapor deposition (MOCVD), respectively. Following the analyses of our results, we have attributed the mechanism of the THz generation from these InN samples to the destructive interference between optical rectification and photocurrent surge. Under the average intensity of 176 W cm −2 for the subpicosecond laser pulses at 782 nm, the THz output powers were measured to be as high as 2.4 μW from the 220 nm InN film, with the output frequencies spanning the band from 300 GHz to 2.5 THz.

We have investigated characteristics of THz waves generated by using a regenerative amplifier in InN micropyramids. Our experimental results indicate that when the density of the micropyramids becomes sufficiently high, the THz output power is dramatically enhanced. In comparison, the PL intensity stays more or less a constant regardless of the density. By measuring the dependences of the THz output power and polarization on the incident angle and pump polarization angle, we have deduced the contributions to the THz output powers from optical rectification and photocurrent surge.

Using a variational procedure within the effective-mass approximation, we have made a theoretical study of the effects of hydrostatic pressure and applied electric fields on the binding energy of a shallow-donor impurity in square-transversal section GaAs-Ga 0.7 Al 0.3 As quantum-well wires. The electric field is applied in a plane of the transversal section of the wire and many angular directions are considered. The hydrostatic pressure has been considered both in the direct and indirect gap regime for the Ga 0.7 Al 0.3 As material. For the potential barrier that defines the wire region, we consider an x-dependent finite and y-dependent infinite model. The results we present are for the impurity binding energy and considering different values of the wire dimensions, hydrostatic pressure, applied electric field, and the impurity position in the transversal section of the wire.

Ce travail aété successivement effectué au Laboratoire d'Optique Appliquée et au Laboratoire d'Optique et Biosciences. Je remercie Danièle Hulin et Jean-Louis Martin de m'avoir accueillie dans d'excellentes conditions dans leurs laboratoires respectifs. Je suis particulièrement reconnaissanteà Jean-Louis Martin pour son enthousiasme et son soutien de tous les instants. Je suis heureuse de m'être trouvée membre de l'équipage pour le début de l'aventure LOB, des séminaires du jeudi aux périples insulaires. Je tiensà exprimer toute ma reconnaissanceà Claude Fabre, Eric Freysz, Bertrand Girard, David Jonas et Arnold Migus pour m'avoir fait l'honneur de participerà mon jury. Mercià Eric Freysz et Bertrand Girard d'avoir de surcroît accepté la lourde tâche de rapporteur. Je remercie ma bonneétoile d'avoir placé ce travail sous la direction de Manuel Joffre. Sa patience, sa qualité d'écoute et sa disponibilité ont su garder le navire de bien des tempêtes. Il a discernéà l'horizon une belleîleà atteindre. Son sensétonnant et sûr de la navigation scientifique a guidé sans cesse ce voyage jusqu'à destination, faisant fi des brouillards, deś ecueils et des fantômes trompeurs. Merci, merci, merci Manuel. Sans GPS ou sextant, sans longue-vue (ou jumelles.. .) pas de voyage ! Toute ma gratitude doncà Xavier Solinas qui a construit pour nous mille ingénieusesélectroniques sans lesquelles assurément nous aurions perdu la route. Pour les belles et astucieuses pièces mécaniques qui ont donnéà l'esquif-manip son allure de fier bâtiment, je remercie Jean-Lou Charles, Daniel Milly et Marcel Bierry. Mercis particuliersà Marcel Bierry pour avoir de plus réalisé avec diligence, dextérité (et style !) une belle coque verte au vaisseau-manip pour le protéger des vents mauvais. Mercià Jean-Pierre Likforman et Adeline Bonvalet qui ont bien voulu venir avec moi sur le pont tirer des bouts dans les jours de tourmente ! Je tiens tout spécialementà remercier Adeline Bonvalet pour avoir d'un oeil serein surveillé la lueur rouge de notre phare-oscillateur et pour avoir construit d'un tour de main expert le bateau-dans-la-bouteille qu'est le Chideuportatif. Je suis très reconnaissanteà Antigoni Alexandrou, Adeline Bonvalet, James Fraser, Ma Maman et Thomas Polack pour leur lecture attentive, critique et/ou orthographique de ce tapuscrit-journal de bord. J'y ajoute de vifs remerciementsà James et Thomas pour nos longues et stimulantes discussions scientifiques.. .. .. . A tous les vaillants marins, les charmantes sirènes, les mouettes moqueuses, les dauphins joueurs et autres poissons volants et multicolores qui ont accompagné la traversée avec gentillesse, bonne humeur, l'enrichissant de thés partagés, de conseils utiles pour la thèse ou le monitorat et de précieuses discussions et explications scientifiques (et même, pour les plus généreux/inconscients, de prêts tangibles de matériel !) grands mercis ! Mercis doncà Anti

We demonstrate broadband infrared pulse shaping by difference-frequency mixing of two visible phase-locked linearly chirped pulses in GaAs. Control of the temporal profile of the emitted field is achieved through this direct tailoring of the exciting visible intensity. The results are in agreement with a simulation with no adjustable parameter.

THz radiation finds various applications in science and technology. Pump−probe experiments at free-electron lasers typically rely on THz radiation generated by optical rectification of ultrafast laser pulses in electro-optic crystals. A compact and cost-efficient alternative is offered by the Smith−Purcell effect: a charged particle beam passes a periodic structure and generates synchronous radiation. Here, we employ the technique of photonic inverse design to optimize a structure for Smith− Purcell radiation at a single wavelength from ultrarelativistic electrons. The resulting design is highly resonant and emits narrowbandly. Experiments with a 3D-printed model for a wavelength of 900 μm show coherent enhancement. The versatility of inverse design offers a simple adaption of the structure to other electron energies or radiation wavelengths. This approach could advance beam-based THz generation for a wide range of applications.

The unit of grating groove density was incorrect (on page 091196-1 in the caption of Fig. 1, on page 091196-2 in Fig. 2, and on page 091196-2 column 1 line 39). The correct groove density of the grating used in this study should be 1800 mm À1 and not 1800 cm À1. Figure 2 should be replaced by the following figure, where annotations are modified to show the correct values. These corrections do not affect any other part of the article and conclusions. 1

Nonlinear optical rectification in asymmetric double quantum well. The fundamental interstate transition is not necessarily the larger one. The fundamental interstate transition depends on the configuration. The increment in the dimensions leads to redshift of resonant peak. The electric field enhances the nonlinear optical rectification response.