Transient phase masks in high-harmonic generation

2007

Abstract High-order harmonic upconversion of femtosecond lasers produces a unique source of short-wavelength light with femtosecond-to-attosecond pulse duration. However, because the involved nonlinear medium is a partially ionized gas, traditional approaches for phase-matching the conversion process are not applicable. This severely limits the flux from this source. Here, we demonstrate the first use of a train of counterpropagating light pulses to enhance high-harmonic emission.

Physical Review Letters, 1997

We demonstrate that two harmonic sources generated independently in a xenon gas jet using the same picosecond Nd:YAG laser are locked in phase. The experiment is performed by separating a laser beam into two parallel beams focused at different locations under the nozzle of a gas jet, and therefore producing two independent sources of harmonic radiation, and studying the pattern obtained in the far field when the radiations from these sources interfere. A high and robust fringe visibility is obtained. [S0031-9007 03735-6] PACS numbers: 32.80.Rm, 42.65.Ky

Physical Review A, 1999

We study experimentally how to control and improve phase matching of high-order harmonic generation. We use a birefringent lens and a birefringent compensator to obtain a fundamental laser pulse ͑150 fs, 800 nm, ϳ4 mJ͒ with two foci separated by 6.2 mm along the propagation axis and with a controllable phase delay between the polarizations along the optic axes of the birefringent optical components. This enables us to enhance the high-order harmonic conversion efficiency for the high-order harmonics in neon to 3ϫ10 Ϫ8 , a factor of 4 higher compared to a single-focus setup in similar conditions. The enhancement is achieved by improving the phase matching and at the same time maintaining a high intensity in a large generating volume.

Physical Review Applied, 2021

We generate high-order harmonics in gaseous medium with tunable photon energy using time domain interferometry of double pulses in a non-collinear generation geometry. The method is based on the fact that the generated harmonics inherit certain spectral properties of the driving laser. The two temporally delayed ultrashort laser pulses, identical in all parameters, are produced by a custom-made split-and-delay unit utilizing wave front splitting without a significant energy loss. The arrangement is easy to implement in any attosecond pulse generation beamline, and is suitable for the production of an extreme ultraviolet source with simply and quickly variable central photon energy, useful for a broad range of applications.

Applied Physics B: Lasers and Optics, 2002

Applied Physics B, 2002

l. roos 2 d. descamps 2 m.b. gaarde 2 a. l'huillier 2 e. constant 3 e. mevel 3 d. von der linde 4 a. orisch 4 a. tarasevitch 4 u. teubner 5 d. klöpfel 5 w. theobald 5

Journal of Physics B: Atomic, Molecular and Optical Physics, 2012

Over the last decade, the control of atomic-scale electronic motion by optical fields strong enough to mitigate the atomic Coulomb potential has broken tremendous new ground with the advent of phase-controlled high-energy few-cycle pulse sources. Further investigation and control of these physical processes, including high-harmonic generation, ask for the capability of waveform shaping on sub-cycle time scales, which requires a fully phase-controlled multiple-octave-spanning spectrum. In this paper, we present a light source that enables sub-cycle waveform shaping with a two-octave-spanning spectrum and 15 µJ pulse energy based on coherent synthesis of pulses with different spectra, or wavelength multiplexing. The synthesized pulse has its shortest high-field transient lasting only 0.8 cycles (amplitude FWHM) of the centroid frequency. The benefit of the approach lies in its modular design and scalability in both bandwidth and pulse energy. Full phase control allows for the synthesis of any optical waveform supported by the amplified spectrum. A numerical study shows the uniqueness of the light source for direct isolated soft-x-ray pulse generation based on high-harmonic generation, greatly reducing and eventually even eliminating the need for gating techniques or spectral filtering. The demonstrated system is the prototype of a class of novel optical tools for attosecond control of strong-field physics experiments.

CLEO: 2011 - Laser Science to Photonic Applications, 2011

By successful fabrication of fine twin structure, QPM SHG at 193 nm is achieved in crystalline quartz. Mechanical module suppressing switch back of twins enables stable wavelength conversion for all-solid-state compact vacuum-ultraviolet laser.

Physical Review Letters, 2000

Phase-matched relativistic harmonic generation in plasmas is observed for the first time. Thirdharmonic light is detected and discriminated spectrally and angularly from the harmonics generated from competing processes. Its angular pattern is a narrow forward-directed cone, which is consistent with phase matching of a high-order transverse mode in a plasma. The signal level is found to be on the same order of magnitude for a circularly polarized pump pulse as for a linearly polarized pump pulse. PACS numbers: 52.40.Nk, 42.65.Ky It had been predicted theoretically [1,2] and recently verified experimentally that the free electrons in the focus of a high-intensity laser [3] will oscillate relativistically and thus emit harmonics with unique angular patterns . This process, known as relativistic nonlinear Thomson scattering, scatters light into a broad range of angles (ϳ180 ± ) with each lobe having a .30 ± angular width for the low-order harmonics. In this paper we report the experimental observation of the third harmonic emitted into a narrow, hollow cone pointing in the direction of laser propagation. To explain these results, a new theory is presented that describes how phase matching in a plasma can result provided that the harmonic radiation has a highorder transverse structure. The signal level of the harmonic for a circularly polarized pump pulse was found to be on the same order of magnitude as that for a linearly polarized pump pulse, which is characteristically different from harmonic generation from electrons bound to atoms. The increased efficiency due to phase matching might eventually lead to interesting coherent, ultrashort-duration and short-wavelength light sources, in which there is much current interest .

2007

We propose a new technique for phase matching high harmonic generation that can be used for generating bright, tabletop, tunable, and coherent x-ray sources at keV photon energies. A weak quasi-cw counterpropagating field induces a sinusoidal modulation in the phase of the emitted harmonics that can be used for correcting the large plasma-induced phase mismatch.