Self-diffraction Process Research Articles

Temporal Contrast Enhancement Based on the Self-Diffraction Process with Different Kerr Media

In this study, the self-diffraction (SD) process proved to be a competitive method to achieve a seed pulse with high temporal contrast in ultra-intense lasers. Several different nonlinear, transparent Kerr media including BK7 glasses, AL2O3 and CVD diamonds were compared experimentally to obtain SD signals with high energy and high conversion efficiency. AL2O3, with a high third-order nonlinear coefficient and high laser damage threshold, was found to be the best medium to improve the conversion efficiency of SD signals. The highest first-order SD signal of 401.7 μJ was achieved, with the conversion efficiency at approximately 9.1%, when the incident pulse energy was 4.40 mJ. The temporal contrast of the obtained first-order SD signal was improved by 7 orders of magnitude to 1012. As a result, this cleaning pulse will facilitate research involving ultra-intense laser systems and high-intensity laser–matter interactions.

Cross-polarized wave-generation-based single-shot fourth-order autocorrelator.

A single-shot fourth-order autocorrelator based on cross-polarized wave generation (XPW) is proposed for the temporal contrast measurement, where the XPW process has the advantages of higher energy conversion efficiency, more compact setup, and less sensitivity to misalignment in comparison to the self-diffraction process. The measurement dynamic of 1012 is obtained with only 6 mJ input laser pulse, where the input beam for XPW is focused by a cylindrical lens and XPW signal with the energy of 400 µJ and time duration of 27.2 fs is obtained. Furthermore, beta-barium borate crystal with the thickness of 6 mm and cutting angle of 56° is used for the sum-frequency generation process to benefit the correlation efficiency. The compact setup could help explore the temporal contrast property of the high-power laser pulse.

A Self-Diffraction Temporal Filter for Contrast Enhancement in Femtosecond Ultra-High Intensity LaserSupported by the National Natural Science Foundation of China (Grant Nos. 11774410 and 91850209), and the Strategic Priority Research Program of CAS (Grant No. XDB16030200).

We demonstrated a nonlinear temporal filter based on the self-diffraction (SD) process. Temporal contrast enhancement, angular dispersion and spectrum broadening properties of the SD process are investigated in experiment and simulation. Driven by spectral phase well compensated laser pulses with bandwidth of 28 nm, the filter produced clean pulses with a temporal contrast higher than 1010 and excellent spatial profile, the spectrum of which was smoothed and broadened to 64 nm. After implementing this filter into a home-made 30 TW Ti:sapphire amplifier, temporal contrast of the amplified pulses was enhanced to 1010 within the time scale of –400 ps.

Temporal contrast improvement by a self-diffraction process for a petawatt-class Ti:sapphire laser

We demonstrate significant temporal contrast improvement for a petawatt-class Ti:sapphire femtosecond laser by introducing a temporal pulse filter based on a self-diffraction process. A double chirped-pulse-amplification laser system was set up to stretch, amplify and recompress the generated first-order self-diffraction pulse. The maximum energy of 130 μJ has been achieved for one first-order self-diffraction seed pulse. By optimizing the initial chirp value, the spectral bandwidth was slightly broadened for the first-order self-diffraction pulse and the cleaned pulse did not exhibit visible spectral distortions in the air environment. The measurement results for the incident pulse and the recompressed first-order self-diffraction pulse showed that the temporal contrast was improved by seven orders of magnitude, i.e. from ∼105 to ∼1012 at −25 ps before the main pulse. Such a temporal contrast is beneficial for laser-matter interaction experiments with high focused intensity up to 1022 W/cm2.

Suppression of prepulses by a temporal pulse cleaner based on a self-diffraction process for an ultraintense femtosecond laser

In this paper, we suppress prepulses by introducing a temporal pulse cleaner based on a self-diffraction process to an ultraintense and ultrashort chirped-pulse amplification laser facility. The main characteristics of the pulse cleaner are investigated. By optimizing the time delay between two incident pulses and the input energy, the energy of 130 μJ has been achieved for the first-order self-diffraction seed pulse with the maximum conversion efficiency of ∼11%. The spatial beam quality is improved after the pulse cleaner. The first-order self-diffraction seed pulse is stretched, amplified and recompressed by the chirped-pulse amplification technique. The measurement results show that the temporal contrast is improved by more than five orders of magnitude to at least 3 × 1010 for the recompressed first-order self-diffraction pulse when the incident temporal contrast is 1.5 × 105. This enables the laser facility to generate petawatt-class pulses with a nanosecond temporal contrast of higher than 1010.

Temporal contrast improvement based on the self-diffraction process with a cylinder mirror

A cylinder reflective mirror was used to increase incident pulse energy to multi-millijoules in the research of temporal contrast enhancement based on a self-diffraction (SD) process. A 170 μJ first-order SD pulse with temporal contrast improved by 4 orders of magnitude was obtained when incident pulse energy was 5.1 mJ. In order to improve energy-conversion efficiency, a 67/33 beam splitter was used to replace the original 50/50 one. A 265 μJ first-order SD signal was achieved without damage of the glass plate at 3.7 mJ input pulse energy with an energy-conversion efficiency of about 7.1%. The generated SD pulse is expected to be used as the seed of high-contrast and high-power laser systems.

Optical cavity squeezing of multiwave mixing via dark states

We theoretically demonstrate the influence of dark states on single-mode and two-mode optical squeezing in a four-level atomic–cavity coupling system through fifth- and third-order cascade nonlinearity. We first show the cone emissions of self-diffraction and phase-conjugate spontaneous parametric (SP) four-wave mixing processes. Then, we inject a coherent or Einstein–Podolsky–Rosen field into the SP-MWM channels to investigate the corresponding squeezing. The investigations have potential applications in quantum information processing.

Self-diffraction based self-reference spectral interferometry

A new method of characterizing the femtosecond pulse is proposed based on the self-diffraction process in a thin transparent bulk medium and the self-reference spectral interferometry. A simple device is designed based on this technique and is successful in characterizing a ～40 fs pulse at 800 nm centeral wavelength. The result is in accordance with that measured by a commercial self-reference spectral phase interferometry for direct electric reconstruction. Pulses in a spectral range from deep UV to middle IR are expected to be measured by this new method and corresponding simple device.

Self-diffraction of ultrashort laser pulses under resonant excitation of excitons in a colloidal solution of CdSe/ZnS quantum dots

We report self-diffraction processes of two types under resonant excitation of the fundamental electron – hole (exciton) transition in a strongly absorbing colloidal solution of CdSe/ZnS quantum dots (QDs) by high-power picosecond laser pulses. In the first case the absorption saturation (bleaching) at the exciton transition frequency and the Stark shift of exciton absorption line lead to the formation of a transparency channel and self-diffraction of the laser beam from the thus induced round diaphragm. In the second case, self-diffraction of two laser beams, intersecting in a cell with a colloidal QD solution, occurs on the diffraction grating induced by these beams. The physical processes responsible for the nonlinear optical properties of CdSe/ZnS QDs and the found self-action effects are analysed.

Self-referenced spectral interferometry based on self-diffraction effect

A new technique of “self-referenced spectral interferometry” is demonstrated based on a self-diffraction effect and applied to the measurement of femtosecond pulses. The reference pulse is the first-order self-diffraction pulse that is generated in a thin bulk medium by the self-diffraction process from the incident pulses. A proof-of-principle experiment succeeded in characterizing a ∼55 fs pulse at 800 nm and a sub-10 fs pulse at 400 nm. The system can be simultaneously used to measure ultrashort pulses by the self-diffraction based on frequency-resolved optical gating.

Temporal contrast enhancement of femtosecond pulses by a self-diffraction process in a bulk Kerr medium

We demonstrated for the first time the application of a self-diffraction (SD) process in a bulk Kerr medium to improve the temporal, spectral, and spatial qualities of femtosecond laser pulses. A proof-of-principle experiment succeeded in improving the temporal contrast of a femtosecond pulse by four orders of magnitude even in the picosecond region using a 0.5-mm-thick fused silica glass plate by this technique. The energy conversion efficiency from the incident pulses to the two first-order SD signals is about 12%. By the SD process, a laser pulse with smoother spectral shape, higher beam quality, and shorter pulse duration than those of the input pulse was generated. This technique is expected to be used to design background-free petawatt laser system in the future.

Nonlinear model of sequential recording of superimposed holographic gratings in photopolymer composites with allowance for the self-diffraction from spatial harmonics

The problems of sequential recording of superimposed holographic diffraction structures of transmission and reflection types in photopolymer composites have been investigated taking into account an arbitrary degree of photopolymerization nonlinearity and the interference pattern contrast at an arbitrary ratio of the photopolymerization and diffusion mechanisms of recording and self-diffraction processes. A theoretical model for N superimposed phase diffraction structures has been constructed by solving interrelated kinetic equations of photopolymerization for H + 1 spatial harmonics of each diffraction structure. This approach makes it possible to investigate the temporal dynamics of the harmonic amplitudes, spatial profile, diffraction efficiency, and angular selectivity of recorded gratings. The model proposed takes into account the diffraction of recording beams from the first harmonic of the ith grating during formation of the (i + 1)th grating.

Study of self-diffraction process in photoconducting polymer-nematic liquid crystal hybrid structure

The authors present results of the measurements of self-diffraction process inside the nematic liquid crystal cell with a photoconducting polymeric layer poly(N-vinylcarbazole) doped with trinitrofluorenone molecules. The dynamics of diffraction grating fading process versus applied voltage and different Ar+ laser power has been studied. Three-step process of grating’s fading was observed, connected with the charge carrier generation and their mobility in the photoconducting polymer. Theoretical calculations assuming proposed mechanism responsible for the grating decay are in a very good agreement with experimental results.

Efficient holographic recording in novel azo-containing polymer

We report on periodic structures inscribed through holographic recording by both intensity light patterns and polarization patterns in novel azo-containing polymer poly[oxyethylene({6-[4-(biphenyl-4-azo)phenoxy]hexyl}imino) ethylene-carbonylimino(2-methyl-1,3-phenylene)iminocarbonyl] abbreviated as A-TDI. The kinetic of grating recording and diffraction efficiency of recorded gratings using polarized cw Ar+ laser light have been measured for s–s, p–p and s–p polarization configurations. The translation grating technique applied during the light self-diffraction process allowed for investigations of phase and amplitude gratings contributions to light diffraction in the studied polymer. Full reversibility of polarization (s–p) grating recording and observation of a half-period structure development during optical erasure process makes this material a good candidate for further studies as a potential material for dynamic holography purposes.

Polarisation-sensitive holographic recording in polyimide-containing azo-dye

Holographic recording of diffraction gratings in high T g polyimide doped with an azo-dye Disperse Red 1 (DR1) is reported. The recording mechanism performed by laser light within the dye absorption range (632.8 and 532 nm) is due to photo-induced anisotropy in which light induced repeated trans– cis photoisomerisation of DR1 molecules leads, after many steps, to quasi-stable molecular reorientation. The characteristics of gratings recorded by two mutually parallel polarisation beams as well as orthogonal linear polarisation beams (so-called polarisation holographic gratings) were measured via observation of a light self-diffraction process as a function of many experimental parameters.

Self-diffraction from free surface relief gratings in a photorefractive Bi12TiO20 crystal

Experimental results on self-diffraction of periodically phase-modulated laser beams from a relief grating formed on a free surface of a cubic photorefractive Bi12TiO20 crystal due to the piezoelectric effect are reported. Periodic intensity modulations of the reflected beams up to 10−2 due to energy exchange at this unshifted phase grating are measured. The modulation depends linearly on the fringe spacing and on the amplitude of an externally applied electric dc field. The observed self-diffraction process is independent of the light polarization.

Coupled wave analysis of anisotropic conical diffraction in doped (K0.5Na0.5)0.2(Sr0.61Ba0.39)0.9Nb2O6 crystals

Three anisotropic diffraction cones in doped (K0.5Na0.5)0.2(Sr0.61Ba0.39)0.9Nb2O6 crystals with two extraordinary polarized incident beams can be observed for the experimental configuration where the c axis is parallel or perpendicular to the incident plane. These cones are attributed to anisotropic conical self-diffraction and cross-diffraction process, respectively. Photorefractive multiwave interaction caused by the incident beams and forward scattered beams satisfying the phase matching condition is proposed to explain the experimental results. The coupled wave equations and its numerical solution including anisotropic self-diffraction and cross diffraction are also presented. Theoretical analysis and experimental results show that anisotropic conical cross-diffracted light arising from the contribution of both incident beams.

Transformation of pulse characteristics via cascaded second-order effects in an optical parametric amplifier

We have demonstrated the linear transformation of a pulse chirp through second-order cascading in a degenerate phase-matched optical parametric amplifier by means of the self-diffraction process. We have measured as much as seven-fold enhancement of a frequency sweep rate in the diffracted idler pulses with no visible onset of intensity-dependent effects.

On the dynamic self-diffraction in methylene blue-sensitised gelatine

Dynamic self-diffraction processes have been observed and analysed for methylene blue-sensitised water-swollen gelatine (MBSG). A degenerate two-wave mixing experiment performed on thick samples of MBSG with 10 mW, 632.8 nm wavelength He Ne laser light allowed for the formation of phase- and amplitude-transient holographic gratings. Single-beam propagation characteristics through MBSG were measured with a Mach-Zehnder interferometer. The observed energy transfer between the writing beams in the two-beam coupling experiment and the considerable temporal oscillations of diffraction efficiency are explained by simple formulae. Two processes are considered: the time-dependent phase shift between the writing beams and the transverse self-phase modulation effects (self-focusing and interference ring formation).

Parametrically induced light diffraction in crystals with second-order susceptibility

The theoretical description of parametric cascaded processes produced by intersecting beams in crystals with second-order susceptibility is presented. A common system of equations in the Slowly Varying Amplitude (SVA) approximation is used to treat the phenomenon. This approach provides a description of overall self-diffraction processes and the equations are well suited for numerical simulations. A relation between phase-matching conditions for parametric cascading processes and diffraction efficiency is found. Pump depletion influence is analysed. The results of numerical simulations are in good agreement with experimental data.