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We report on experimental and theoretical studies of widely tunable high-efficiency subnanosecond optical parametric generator (OPG) and amplifier (OPA) based on a 2 cm long multigrating MgO-doped periodically-poled lithium niobate (MgO:PPLN) crystal pumped by a passively Q-switched Nd:YAG micro-laser. Our OPG can be continuously tuned from 1442 nm to 4040 nm with signal wave energies ranging from 33 μ J to 265 μ J and total OPG conversion efficiency up to 46 % that depended on the pump focusing conditions. Characterization of spatial properties of the OPG determine Lorentzian spatial profile of the signal beam with M 2 ≈ 2 that was also dependent on the pump focusing conditions. High OPG gain and subsequent pump depletion led to the adjustment of the output signal pulse duration in the range of 242 – 405 ps by varying the incident pump power. By using a distributed feedback (DFB) continuous-wave (CW) 1550 nm wavelength seed laser for the OPA operation we reduced the generation threshold up to 1.6 times, increased maximum conversion efficiency by 4 – 20%, and achieved nearly transform-limited output signal pulses. Experimentally measured characteristics were supplemented by numerical simulations based on the quantum mechanical model for the OPG, and classical three-wave interaction model for the OPA operation.

We report an experimental realization of a subnanosecond optical parametric amplifier (OPA) system in a beta barium borate (BBO) crystal pumped by the third harmonic of a passively Q-switched Nd:YAG microlaser system and seeded by the continuum generated in a photonic crystal fibre (PCF). It yields broadband continuous signal wavelength tunability in the visible spectrum range from 470 to 660 nm and the idler wavelength from 768 to 1450 nm. Besides the experimental data, the numerical simulation results of the BBO optical parametric amplifier are presented. The maximum output power of the subnanosecond BBO OPA is limited by laser induced damage in the BBO crystal by the pump radiation and seed radiation spectral power density. We also notice and discuss the effect of seed radiation on BBO OPA output radiation characteristics. The numerical simulations qualitatively agree with the experimental data.

Terahertz and third-harmonic generation by tightly focused bichromatic femtosecond pump pulses with comparable input intensities in air is studied both experimentally and theoretically. Plasma-assisted temporal shifts in the field of intense laser pulses are shown to lead to the time delay between the pump pulses in the vicinity of the focus. This delay can be compensated by the initial time delay that is evidenced by the measured as well as calculated correlation functions of the fundamental and second harmonics. The possibility to characterize the plasma channel length from the correlation function is discussed.

A singly resonant synchronously pumped optical parametric oscillator (SPOPO) based on the experimental setup of J. Opt. Soc. Am. B 36, 131 (2019)JOBPDE0740-322410.1364/JOSAB.36.000131 is studied theoretically. Stable, oscillatory, and chaotic operation modes of the SPOPO are investigated. The need of the self- and cross-phase modulation terms in the theoretical model for the explanation of the instabilities is demonstrated. The theoretical values of the wavelengths of the signal spectrum maxima are found. The evidence of chaos by the calculation of the Lyapunov exponent is provided. The possibilities to avoid the instabilities are discussed.

Here we present an experimental as well as theoretical study of third-harmonic generation in tightly focused femtosecond filaments in air at the wavelength of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$1.5 \,\upmu \hbox {m}$$\end{document}1.5μm. At low intensities, longitudinal phase matching is dominating in the formation of 3rd harmonics, whereas at higher intensities locked X-waves are formed. We provide the arguments that the X-wave formation is governed mainly by the tunnel-like ionization dynamics rather than by the multiphoton one. Despite of this fact, the impact of the ionization-induced nonlinearity is lower than the one from bound–bound transitions at all intensities.

We present analytical solutions to nonlinear coupling equations for parametric down-conversion of a broadband pump at large gain. The feasibility of analytical expressions is demonstrated for the case of a collinear type II parametric interaction in beta-barium borate crystal and group-velocity matching of signal and pump waves. The correlation function of amplified signal wave is obtained, and it is revealed that the bandwidth of a noise-seeded optical parametric amplifier increases with a decrease in pump pulse duration, especially for femtosecond pump pulses.

We present experimental data and numerical simulation results obtained during investigation of synchronously pumped optical parametric oscillator (SPOPO) pumped by femtosecond Yb:KGW laser (central wavelength at 1033 nm). The nonlinear medium for parametric generation was periodically poled potassium titanyl phosphate crystal (PPKTP). Maximum parametric light conversion efficiency from pump power to signal power was more than 37.5% at λ s =1530 nm wavelength, whereas the achieved signal wave continuous tuning range was from 1470 nm to 1970 nm with signal pulse durations ranging from 91 fs to roughly 280 fs. We demonstrated wavelength tuning by changing cavity length and PPKTP crystal grating period and also discussed net cavity group delay dispersion (GDD) influence on SPOPO output radiation characteristics. The achieved high pump to signal conversion efficiency and easy wavelength tuning make this device a very promising alternative to Ti:sapphire based SPOPOs as a source of continuously tunable femtosecond laser radiation in the near and mid-IR range.

Optical parametric amplification of an input narrowband signal beam in the field of a spatially incoherent conical pump is investigated. Two amplification regimes – onset and exponential – are distinguished. The possibility to amplify the signal beam significantly and obtain a smooth intensity profile at the output is revealed. It is shown that the incoherent conical beam may act on the signal beam as a plane wave. Good agreement of theoretical and experimental data is obtained.

We present detailed experimental data and numerical simulation results obtained during the investigation of temporal characteristics of synchronously pumped optical parametric oscillator (SPOPO) based on a periodically poled potassium titanyl phosphate crystal (PPKTP). A femtosecond Yb:KGW laser was used for SPOPO pumping and signal pulse durations were measured in the 1.49-1.82 m spectral range at three different conditions of cavity losses. The experimental investigation and numerical modeling showed strong SPOPO signal pulse duration dependency on the transmission of the output coupler. We also used external group delay dispersion (GDD) compensation to achieve shorter SPOPO signal pulses

Geometric phase retarders—such as q-plates and S-waveplates—have found wide applications due to simplicity of operational principles and flexibility for the generation of azimuthally symmetric polarization states and optical vortices. Ellipticity of the polarization vector and phase of the generated beam strongly depend on the retardation of the plate. Real devices usually have retardation value slightly different than the nominated one. Previously unattended perturbation of the retardation leads to asymmetry in intensity distribution and variation of ellipticity of the local polarization vector of the generated beam. We elucidate that controlled and intentionally driven azimuthally variable, oscillating perturbation of the retardation reveals the possibility to avoid distortions in the generated beam and leads to the recovery of the symmetrically distributed intensity and polarization (with zero ellipticity) of the beam. Described recovery of the desired polarization state could find application for generation of the high purity beam with azimuthally symmetric polarization, in which the local polarization ellipse has zero ellipticity.

The broadband infrared (in the range of 2 μm) and visible radiations were generated in air by focused two-color (wavelengths of about 791 nm and 1.2–1.6 μm, respectively) femtosecond laser pulses. The spectral and angular properties of the radiation generated in both spectral ranges allowed us to interpret it as a result of the interplay between spectral broadening and cascaded four-wave mixing of the incident and frequency-shifted light fields. Results of the numerical modeling of the propagation equation including the nonlinear Kerr term agree well with the experiment.