Sub-poissonian light in third-harmonic generation: Quantum predictions via classical trajectories

Sub-Poissonian light in the third-harmonic generation process is studied numerically and analytically. Special regime exhibiting the time-stable maximum sub-Poissonian behaviour with the Fano factorF ≈ 0.81 is found and analyzed. Theoretical prediction of the Fano factor and explanation of the extraordinary time stability of the sub-Poissonian behaviour are given using the semiclassical method of classical trajectories.     

Two-photon-resonant third-harmonic generation in cesium vapor

It is shown that two-photon-resonant tripling of the ruby laser frequency in cesium vapor is limited by ionization. The laser induced Stark shift is found to be favorable to the process in that it counteracts saturation of the resonant transition.     

Picosecond third-harmonic light generation in calcite

The third-harmonic generation of picosecond light pulses in a calcite crystal is studied experimentally and theoretically. A passively mode-locked Nd: phosphate glass laser is used in the experiments. The third-order nonlinear susceptibility components and the effective third-order nonlinear susceptibility of type II phase-matched (ooee) thirdharmodic generation are determined.On leave from Shanghai Institute of Optics and Fine Mechanics, Academia Sinica, Shanghai, P.R. China     

Nanocrystal-size-sensitive third-harmonic generation in nanostructured silicon

Third-harmonic generation (THG) in reflection geometry was studied in nanostructured silicon layers grown by electrochemical porosifying of p-type (110) silicon substrates. An order of magnitude enhancement of the THG efficiency compared to crystalline silicon (c-Si) was observed for the samples prepared on a highly doped substrate, whereas for the samples grown on a low-doped substrate the THG was much less efficient than for c-Si. The finding is discussed in terms of fluctuations of the electric field of the pump-laser irradiation in the layers of anisotropically distributed silicon nanocrystals. Received: 26 July 2002 / Revised version: 9 January 2003 / Published online: 3 April 2003 RID="*" ID="*"Corresponding author. Fax: +7-95/939-1566, E-mail: leo@vega.phys.msu.su     

Phase-matched third-harmonic generation in dye solutions

Various dyes are investigated for their capability of generating 3^rd harmonic of Nd-laser light. The feasibility of achieving phase matching is demonstrated by direct measurements of the index of refraction. Third-harmonic conversion of hexamethylindocarbocyanine iodide, diethyloxacarbocyanine iodide and fuchsin red are compared. The highest conversion is obtained for hexamethylindocarbocyanine iodide (80 times higher than in fuchsin red). A further enhancement of the third harmonic by a factor of 70 is expected for the fundamental laser light at 1.15 μm.     

Inverse problem of cascaded third-harmonic generation

Based on some numerical techniques such as split-step Fourier transformation, fourth-order Runge-Kutta and successive iteration method, the fundamental field was calculated from the known third-harmonic (TH) field in the process of TH generation (THG) using one doubling and one mixing KDP crystals. The effects of the monochromatic initial fields on the iteration numbers and the calculation precision were discussed. The inverse solution of the broadband laser pulse with linear frequency chirp was also carried out. The results show that the method proposed in this paper is available and efficient, which gives a new way to design and optimize the process of THG.     

High-power third-harmonic flat pulse laser generation

The generation of a high-power laser pulse at 266 nm that is longitudinally shaped according to a prefixed intensity profile is reported. The main features of the pulse shape modifications due to second- and third-harmonic conversions are measured, and the results are in good agreement with the theory. The UV temporal shape depends on the chirp of the fundamental pulse and on the crystal phase-matching angle. Exploiting the large stretching imposed on the third-harmonic signal, we show that the pulse intensity profile can be obtained by spectral single-shot measurements.     

Structure sensitivity in third-harmonic generation microscopy

We characterize experimentally the influence of sample structure and beam focusing on signal level in third-harmonic generation (THG) microscopy. In the case of a homogeneous spherical sample, the dependence of the signal on the size of the sphere can be controlled by modifying the Rayleigh length of the excitation beam. More generally, the influence of excitation focusing on the signal depends on sample geometry, allowing one to highlight certain structures within a complex system. We illustrate this point by focusing-based contrast modulation in THG images of Drosophila embryos.     

Multicrystal designs for efficient third-harmonic generation

Efficient frequency tripling of high-fluence, narrow-band laser pulses is routinely accomplished with a doubling crystal and a sum-frequency mixer. The addition of a second mixer can dramatically improve conversion efficiencies for the large bandwidths of interest for inertial confinement fusion. Designs that involve two doublers similarly offer a higher dynamic range of conversion efficiency versus intensity than the usual two-crystal design.     

脉冲激光频域干涉技术在超快动力学物理中的应用

介绍了一种具有fs时间分辨力的超短脉冲激光频域干涉测试技术,详细论述了该技术的工作原理和系统构成,指出传输时间差和相位差是影响频域干涉条纹周期的主要因素。采用脉冲激光频域干涉仪测量了200 nm厚度铝膜在波长800 nm、单脉冲能量0.7 mJ、脉宽35 fs脉冲激光作用下的运动速度剖面。在单次飞秒脉冲激光作用下,铝膜自由面的运动速度峰值可达960 m/s,速度剖面的上升前沿小于5.77 ps,表明脉冲激光频域干涉技术可用于测量材料在超快脉冲激光作用下的冲击动力学参数。     

脉冲激光频域干涉技术在超快动力学物理中的应用

介绍了一种具有fs时间分辨力的超短脉冲激光频域干涉测试技术,详细论述了该技术的工作原理和系统构成,指出传输时间差和相位差是影响频域干涉条纹周期的主要因素。采用脉冲激光频域干涉仪测量了200 nm厚度铝膜在波长800 nm、单脉冲能量0.7 mJ、脉宽35 fs脉冲激光作用下的运动速度剖面。在单次飞秒脉冲激光作用下,铝膜自由面的运动速度峰值可达960 m/s,速度剖面的上升前沿小于5.77 ps,表明脉冲激光频域干涉技术可用于测量材料在超快脉冲激光作用下的冲击动力学参数。     

Modification of solitary waves by third-harmonic generation

The effect of phase-matched third-harmonic generation on the structure and stability of spatial solitary waves is investigated. A power threshold for the existence of two-frequency spatial solitons is found, and the multistability of solitary waves in a Kerr medium owing to a higher-order nonlinear phase shift caused by cascaded third-order processes is revealed.     

Phase-matched third-harmonic generation in highly germanium-doped fiber

Phase-matched third-harmonic generation is demonstrated in a germanium-doped optical fiber. Green light at 514.4 nm is generated in an LP(03) mode when a pump field at ~1543.3 nm is launched into the fiber in the fundamental LP(01) mode. The phase matching is achieved for a particular combination of the germanium doping concentration and the fiber core diameter.     

Phase-matched third-harmonic generation in anisotropically nanostructured silicon

A frequency-tunable laser system based on an optical parametric oscillator is used to implement phase-matched third-harmonic generation in porous silicon films with a strong form birefringence. Phase matching, orientation dependences, and the behavior of the third harmonic as a function of the thickness of an absorbing film are confirmed by calculations and linear-optical measurements.     

Semi-classical theory of two-photon resonant third-harmonic generation

A semi-classical density matrix theory based on the Method of Averages is used to derive an expression for the third-harmonic generation intensity I^3ω as a function of the fundamental intensity I^ω in the neighbourhood of a two-photon resonance. The result takes account of optical Stark shifts, two-photon saturation and both homogeneous and inhomogeneous broadening. At high intensities, I^3ω∝I^ω, in contrast to the case where optical Stark shifts are ignored for which I^3ω∝(I^ω)^-1.     

Atmospheric influences in optical third-harmonic generation experiments

Third-harmonic generation in a thin solid plate surrounded by a gas is investigated. We conclude that atmospheric contributions can be suppressed in third-harmonic generation from thin solid plates. A phase-sensitive measurement of the third-order susceptibility of gases is proposed. We calibrated the third-order susceptibility of air to be X⁽³⁾ _a=(3.4±1.5)×10^–18 esu with a phase uncertainty of ±10°.     

Depth-resolved multiphoton polarization microscopy by third-harmonic generation

We achieve depth-resolved polarization microscopy by measuring third-harmonic generation induced by a tightly focused circularly polarized beam. In crystals exhibiting strong birefringence this signal is dominated by positively phase-matched third-harmonic generation. This process occurs in only optically anisotropic media, in which the birefringence compensates for the phase mismatch between the fundamental and the third harmonic induced by dispersion. Both the intensity and the polarization of the emitted signal provide information on the local optical anisotropy. We demonstrate the technique by imaging biogenic crystals in sea urchin larval spicules.     

Optimal conditions for third-harmonic generation in gas mixtures

The authors consider the effect of the buffer gas nonlinear susceptibility on the third-harmonic generation efficiency in gas mixtures. Experiments were performed in mixtures of krypton with xenon, argon and nitrogen at the wavelength of hydrogen Lyman-α. The optimal compositions for these mixtures were found and the gain in the generation power against the pure gas was estimated.     

Characterization of third-harmonic generation from femtosecond laser-excited silicon

Third-harmonic generation (THG) from silicon crystals excited by femtosecond pulses has been studied. THG as a function of probe pulse delay from linear and circularly polarized probe pulses was examined. Both polarizations exhibit a fast, 300 fs drop in THG when the Si is pumped by pulses with fluence above the melting threshold. This drop for both polarizations indicates that electronic effects dominate THG in laser-melted Si since structural effects should principally influence THG from linearly polarized probes, suggesting that care needs to be exercised in interpreting THG signal as an ultrafast probe of crystalline structure in semiconductors.