Tunable Optical Parametric Generator Research Articles

Tunable narrow-linewidth high-peak-power sub-nanosecond optical parametric generator by injection seeding.

We present an efficient tunable optical parametric generator (OPG) with its linewidth close to the Fourier transform limit by injection seeding a tunable diode laser. Benefitting from high-peak-power sub-nanosecond (426 ps) laser pumping and a high-gain MgO:PPLN (PPMgLN) crystal, the OPG produced signal peak power up to 0.343 MW at 1638 nm and the total conversion efficiency reached 47.9% at 1-kHz pulse repetition rate. Considering the linewidth limit of short signal pulses (∼ 350 ps), a tunable seeder with the linewidth at hundred-MHz level was applicable. The achieved OPG signal tuning range was 1510-1638 nm with linewidth at GHz level, which is two orders of magnitude narrower than the unseeded OPG. Injection seeding a non-resonant OPG device does not introduce extra cavity feedback electronics that are essential for an optical parametric oscillator (OPO), greatly improving robustness and reducing cost. It is believed such a compact, tunable and costless PPMgLN OPG with high peak power, high repetition rate and relatively narrow linewidth has great significance in lidar, spectroscopy, etc.

Efficient MW-peak-power kHz-repetition-rate sub-nanosecond optical parametric generator tunable from near- to mid-infrared

A high-efficiency, high-peak-power, widely tunable optical parametric generator (OPG) based on a multi-period MgO-doped periodically poled lithium niobite (PPMgLN) crystal is presented. Pumped by a passively Q-switched microchip Nd:YAG laser with the pulse duration of 330 ps and repetition rate of 1 kHz, the OPG could be continuously tuned from 1399 nm to 4443 nm by changing the grating period and working temperature. The total output power of the signal and idler waves reached 591 mW, corresponding to the conversion efficiency of 67.2% and slope efficiency of 89.6%, the highest as far as we know. The maximum signal peak power was over 1.6 MW at 1758 nm. The evolution of line width and beam profile of the signal wave during wavelength tuning were also studied and the theoretical models were proposed.

Tunable optical parametric generator based on the pump spatial walk-off.

We suggest a novel optical parametric generator (OPG) in which one of the downconverted beams is spontaneously generated along the Poynting vector of the pump beam. In this configuration, the generation takes advantage of the walk-off of the extraordinary pump, rather than being degraded by it. As a result, the generated signal and idler beams are bright due to a high conversion efficiency, spatially nearly single mode due to the preferred direction of the Poynting vector, tunable over a wide range of wavelengths and broadband. The two beams are also correlated in frequency and in the photon number per pulse. Furthermore, due to their thermal statistics, these beams can be used as a pump to efficiently generate other nonlinear processes.

Broadband and tunable optical parametric generator for remote detection of gas molecules in the short and mid-infrared.

The development of a novel broadband and tunable optical parametric generator (OPG) is presented. The OPG properties are studied numerically and experimentally in order to optimize the generator's use in a broadband spectroscopic LIDAR operating in the short and mid-infrared. This paper discusses trade-offs to be made on the properties of the pump, crystal, and seeding signal in order to optimize the pulse spectral density and divergence while enabling energy scaling. A seed with a large spectral bandwidth is shown to enhance the pulse-to-pulse stability and optimize the pulse spectral density. A numerical model shows excellent agreement with output power measurements; the model predicts that a pump having a large number of longitudinal modes improves conversion efficiency and pulse stability.

Widely and continuously tunable optical parametric generator infrared laser

The experimental results of a high efficiency infrared laser are demonstrated on a quasi phase matched optical parametric generator in PPMgLN (5% MgO doping) pumped by a 1064 nm Nd:YAG laser. A broad continuous signal spectrum 1.56–1.67 μm are obtained by tuning the crystal temperature from 20°C to 200°C. When the average pump power is 1.82 W with about 70 ns pulse duration operating at a repetition rate of 10 kHz, the maximum total output power of the PPMgLN OPG is about 323.58 mW consisting of 210 mW of 1.639 μm signal radiation and 113.58 mW of 3.02 μm idler radiation.

Modulation of spatial spectrum in tunable two crystal optical parametric generator

We report on theoretical and experimental investigations of two crystal traveling-wave optical parametric generator (OPG). It is shown that the efficiency and angular structure of traveling-wave tunable OPG output depends on the distance between the two crystals. Air dispersion driven efficiency modulation at different OPG output wavelengths is observed experimentally and confirmed by theoretical calculations.

Widely and continuously tunable optical parametric generator based on MgO-doped periodically poled LiNbO3 crystal

A widely tunable quasi-phase-matched optical parametric generator pumped by a 1064 nm acousto-opticallyQ-switched diode-end-pumped Nd: YAG laser based on a MgO-doped periodically poled LiNbO3 crystal with a multigrating structure (29.2–30.4 μm) is reported. A broad continuous signal spectrum 1513–1731 nm is obtained by changing the crystal grating periods from 29.2 μ to 30.4 μ and by tuning simultaneously the crystal temperature from 60°C to 150°C. When the average pump power is 1.82 W with about 120 ns pulse duration operating at a repetition rate of 10 KHz, the maximum total output power of the PPMgLN OPG is about 323.58 mW consisting of 210 mW of 1.639 μm signal radiation and 113.58 mW of 3.02 μm idler radiation.

Raman gain measurements and photo-induced transmission effects of germanium- and arsenic-based chalcogenide glasses

The Raman gain spectra of millimeter thick As(2)S(3) and As(24)S(38)Se(38) glasses and Ge((23 - x))Ga(x)Sb(7)S((70 - y))Se(y) with x = 0 and 5 and y = 0, 2, 5 have been measured using a direct nonlinear optics technique. The pump light originated from a picosecond Nd:YAG laser operating at 1064 nm and a tunable optical parametric generator and amplifier (OPG/OPA) was used as a source for the probe light. A peak material Raman gain coefficient of (155 +/- 11) x 10(-13) m/W has been measured for the As(24)S(38)Se(38) glass. A reversible photodarkening effect which responds to picosecond pulses is also reported. Finally, surface optical damage threshold measurements were found to be less than 9 GW/cm(2) for the reported samples, values which are comparable to some TeO(2)-based glasses with lower nonlinearities.

Optical Properties of Au Nanoparticle Dispersed (Ba,Sr)TiO3 Thin Films

Au nanoparticles dispersed (Ba,Sr)TiO3 thin films were fabricated using alternating sputtering method. With the nominal thickness of Au layer of 1 nm, the spherical Au particles of 3.83 nm size were obtained showing the spatial distribution referred to a Maxell-Garnett type effective medium geometry. The film shows the characteristic surface plasmon resonance absorption band at 571 nm. Based on the effective medium theory, the linear optical functions of the films were characterized. The third-order optical nonlinearity was analyzed by a single beam Z-scan technique with a picosecond pulse laser. The real and imaginary parts of third-order susceptibility can be resolved at several wavelengths around the SPR by virtue of wavelength tunable optical parametric generator. The maximum absolute value of third-order susceptibility as large as 3.847 × 10− 8 esu were obtained at the SPR frequency.

Three- and four-photon absorption of a multiphoton absorbing fluorescent probe

High-order multiphoton excitation processes are becoming a reality for fluorescence imaging and phototherapy treatment because they afford minimization of scattered light losses and a reduction of unwanted linear absorption in the living organism transparency window, making them less susceptible to photodamage, while improving the irradiation penetration depth and spatial resolution. We report the four-photon-excited fluorescence emission of (7-benzothiazol-2-yl-9,-didecylfluoren-2-yl)diphenylamine in hexane and its four-photon absorption cross section sigma4' = 8.1 x 10(-109) cm8 s3 photon(-3) for the transition S0 --> S1 when excited at 1600 nm with a tunable optical parametric generator (OPG) pumped by picosecond laser pulses. When pumped at 1200 nm, three-photon absorption was observed, corresponding to the same transition.

Static and Dynamic Solvation at the Air/Water Interface

The electronic excited-state solvation dynamics of coumarin 314 (C314) adsorbed at the air/water interface was investigated by femtosecond time-resolved second-harmonic generation (TRSHG). The second-harmonic spectrum of C314 at the air/water interface was determined using a tunable optical parametric generator, giving a spectral peak at 419 ± 3 nm. The solvatochromic shift is in good agreement with the recently proposed interfacial polarity scale, which predicts that the empirical polarity parameter of the interface is the arithmetic mean of the two bulk phases. The time-resolved second-harmonic response to the excited-state solvation was measured at two fundamental wavelengths (840 and 900 nm) and with two pump polarizations (S and P). The results indicate that the static spectral peaks of the S- and P-pumped distributions are offset ∼5 nm, while the dynamic interfacial solvation proceeds with two time constants, τ1 = ∼200 fs and τ2 = 1.2 ps, which are independent of C314 interfacial orientation. The sl...