Laser-diode side-pumped actively Q-switched eye-safe intracavity optical parametric oscillator

Eye-safe laser of 1573 nm wavelength from a laser-diode (LD) side-pumped actively Q-switched Nd:YAG/KTP intracavity optical parametric oscillator (IOPO) with acousto-optic (AO) modulator is presented. The dependences of the average output power, the pulse width, pulse energy, and the peak power on incident pump current for the generated-signal-light pulses are obtained. By considering the Gaussian spatial distributions of the pump light in laser medium, the photon densities of the fundamental, the signal, and the idle waves as well as the initial population-inversion density and the coupled rate equations of this IOPO are described, in which the influence of the pump rate, the thermal effect in the gain medium and the change of the photon density along the cavity axis have been also taken into account. These coupled equations are solved numerically, and the theoretical calculations are consistent with the experimental results.     

Compact low-threshold Q-switched intracavity optical parametric oscillator

We report a singly resonant pulsed intracavity KTiOPO>(4) optical parametric oscillator that uses a semi-monolithic microchip laser design. The compact (50-mm-long), low-threshold (1.3-W) cavity uses a novel quadrupole deflector Q switch to give 4-microJ pulses at 1.064 microm and 0.4-microJ signal pulses of 5.6-ns duration at 1.53 microm with a repetition frequency of 5 kHz when it is pumped with a 2-W laser diode. The signal pulses are diffraction limited and single frequency.     

Low threshold narrow pulse width eye-safe intracavity optical parametric oscillator at 1573 nm

We demonstrate a low threshold operation of a KTP-based intracavity optical parametric oscillator, emitting at 1573 nm, driven by a cw diode-end-pumped actively Q-switched Nd:YVO₄ laser. Diode-pump threshold around 0.86 W is achieved, which, to the best of our knowledge, is the lowest one under the similar experimental conditions. Owning to the efficient cavity-dumping effect, a signal pulse width as short as 1.4 ns and peak power higher than 3 kW is obtained, at the incident diode-pump power of 1.3 W and A-O modulating frequency of 9 kHz. Moreover, threshold characteristic for the IOPO is also studied, which is in well agreement with the experimental results.     

Compact 21-W 2-mum intracavity optical parametric oscillator

We report on an intracavity optical parametric oscillator (OPO) placed within a compact diode-pumped Nd:YALO laser cavity. This OPO utilizes a pair of KTP crystals, which are diffusion bonded together in a walk-off-compensated configuration. We have generated up to 21.4 W of 2-mum radiation, operating in a few-kilohertz range.     

Picosecond intracavity optical parametric oscillator

We present a novel technique to generate picosecond pulses at 1.57 microm with kilohertz repetition rates, using an intracavity optical parametric oscillator. With this device we were able to generate up to 120-mW average power at a repetition rate of 2.5 kHz.     

具有腔内光放大的单共振光参量振荡器

推导了描述稳态运行，具有腔内光放大的环形腔单共振光参量振荡器(ICOASRO)的功率特性的高斯光束理论.在这种结构的单共振光参量振荡器(SRO)中，适当地选择光放大器的参数，可以很大程度地降低单共振光参量振荡器的抽运阈值.在平均场近似下无二阶非线性交叉耦合作用的具有腔内光放大的环形腔单共振光参量振荡器的工作范围分成四个工作区域，且存在最小的单共振光参量振荡器的抽运阈值.文中的分析考虑了作为光放大器的激光增益介质的端面抽运特性，考虑了一般化单共振光参量振荡器的特性. 关键词： 单共振光参量振荡器 光放大 阈值     

High-repetition-rate eyesafe intracavity optical parametric oscillator

Received: 15 December 1997/Revised version: 27 April 1998     

Compact low threshold Cr:YAG passively Q-switched intracavity optical parametric oscillator

We report a compact KTP-based intracavity optical parametric oscillator (IOPO) driven by a diode-end-pumped passively Q-switched Nd:YVO₄/Cr:YAG laser. For the first time, we take the thermal lens effect of the Cr:YAG into consideration and discuss its impact on the signal output. Diode pump threshold as low as 0.52 W has been achieved, which is the lowest result reported to date. At the incident diode pump power of 4 W, we obtained the maximum signal average and peak power of 358 mW and 12.5 kW, respectively, corresponding to a diode-to-signal conversion efficiency of 9%. Moreover, cavity-dumping characteristic and pulse transforming process from 1064 to 1573 nm are qualitatively analyzed.     

Compact, efficient 344-MHz repetition-rate femtosecond optical parametric oscillator

We describe configurations of a novel synchronously pumped femtosecond optical parametric oscillator based on the crystal RbTiOAsO(4) and operating with a signal-pulse-repetition frequency as high as 344 MHz. Average signal powers as high as 600 mW and pulse durations of 78 fs are demonstrated at a wavelength of 1.25 microm, and a characterization of the signal output using frequency-resolved optical gating implies asymmetric near-sech(2)(t) intensity-profile pulses with significant amounts of spectral cubic phase.     

Brewster-oriented passive Q-switch intracavity optical parametric oscillator

The behaviour of passively Q-switched solid-state lasers containing intracavity optical parametric oscillators (OPOs) is described, and a model to optimize this system‘s performance is developed. Meanwhile, an Nd:YAG laserpumped KTiOPO4 (KTP) intracavity OPO for eye safe laser output is studied experimentally. A Brewster-oriented bis-(4-dimethylaminodithiobenzil)-nickel (BDN) dye film is employed in laser cavity, which plays the double role of a passive Q-switch and a Brewster plate, to Q-switch the light to increase its intensity and polarize the light so that the polarization plane of fundamental irradiation is perpendicular to the Z-axis of KTP serving as the OPO nonlinear crystal, thereby providing type Ⅱ phase matching conditions to generate 1.572μm eye-safe signal laser. Eye-safe signal radiations of 6.6mJ per pulse at 1.572μm wavelength and pulse width as narrow as 6.0ns (FWHM) were obtained. Peak power was up to 1.1MW.     

Highly stable and efficient KTP-based intracavity optical parametric oscillator with a diode-pumped passively Q-switched laser

We present in this paper a highly stable and efficient KTP-based intracavity optical parametric oscillator with a diode-end-pumped Nd:YVO₄/Cr:YAG passively Q-switched laser. At the incident diode pump power of 4 W, the signal (1.57 μm) and idler (3.29 μm) average output powers up to 580 and 100 mW, respectively, have been achieved. The corresponding conversion efficiency from the input diode pump power to the output signal power is 14.5%, while that to the total OPO output (signal+idler) reaches 17%. To the best of our knowledge, these are the highest conversion efficiencies reported to date. After more than four hours of investigation, the OPO power stability better than 2% has been obtained. In addition, efficient cavity dumping of the IOPO has inevitably led to the short pulse duration (1.6 ns) and high peak power output (8.3 kW) at the signal wave. Additionally, the amplitude and repetition rate fluctuations of the signal pulses are well within 5%. PACS 42.55.Xi; 42.60.Gd; 42.60.Lh; 42.65.Yj     

High peak power eye-safe intracavity optical parametric oscillator pumped by a diode-pumped passively Q-switched ND:GGG laser

By exploiting the diode-end-pumped Nd:GGG/Cr⁴⁺:YAG laser as the pump source, a high peak power gray-trace resistance KTP intracavity optical parametric oscillator at eye-safe wavelength was first demonstrated (to our knowledge). Under the incident diode power of 10 W, the maximum average output power of 320 mW at 1567 nm was obtained with the T = 33% output coupler. The corresponding signal pulse width and repetition rate were respectively 1.4 ns and 5.8 kHz. Due to the greatly reduced pulse repetition rate and short pulse width, the signal peak power was estimated to be as high as 39.4 kW.     

High repetition rate electro-optical-Q-switched intracavity optical parametric oscillator

A high repetition rate electro-optical-Q-switched intracavity optical parametric oscillator (IOPO) is realized by using two RbTiOPO₄ (RTP) crystals as electro-optic (EO) modulator. Three repetitions of the EO modulator ( f _p = 15, 20, and 30 kHz) were applied in the experiment. The pulse width can be minimized to 7ns when the input energy is 24.4 J at three modulating repetitions. The peak power of the signal light increases with reducing the pulse repetition rate. By considering the gradual loss from the delayed switched time of the EO switch, the coupled rate equations of IOPO under the assumption of the uniform distributions of the intracavity photon densities are given and the numerical solution of the equations fits the experimental data well.     

Compact, actively Q-switched optical parametric oscillator

An ultracompact, actively Q -switched optical parametric oscillator (OPO) has been realized that is only 30 mm in length, based on a semimonolithic microchip laser, a quadrupole deflector, and a monolithic periodically poled lithium niobate crystal. The OPO threshold was 550 mW when Nd:YAG was used as the gain material and 590 mW for Nd:Y VO(4), giving signal pulses of as much as 8.7 muJ in energy with Nd:YAG at 1 kHz and 5.9-mu;J pulses with Nd:Y VO(4) at 5 kHz, for 1.2- and 2-W laser diode pumping, respectively. The output was single frequency and could be tuned over the range 1540-3440 nm.     

1.57μm被动调Q光学参量振荡器

在半导体泵浦被动调QNd∶GdVO4/Cr4+∶YAG激光腔内,利用KTP晶体实现了高重复频率的内腔OPO的稳定运转。OPO其信号光转换效率为7%,斜效率为10.3%。当泵浦功率7.3W时,可获得平均功率为0.48W,重频15kHz,脉宽6ns,峰值功率达13KW的1570nm激光输出。     

Efficient intracavity optical parametric oscillator with diode side-pumped electro-optic Q-switched laser

An efficient intracavity single-resonant optical parametric oscillator (OPO) at 1.571-μm eye-safe range using a non-criticaily phase-matched KTP crystal is reported. The OPO is excited by a diode side-pumpedelectro-optic Q-switched Nd:YAG laser at 1.064 μm. Signal pulse of 97 mJ and 3.56 ns is obtained under the input electric energy of 2.3 J, corresponding to a slope efficiency of 4.2%, and a repetition rate range of 1--30 Hz.     

Comparative studies of eye-safe intracavity and extracavity optical parametric oscillators with an unstable telescopic cavity

We have experimentally studied the lasing characteristics of an eye-safe optical parametric oscillator (OPO) with an unstable telescopic cavity when it is placed inside (intracavity OPO) and outside (extracavity OPO) the plane-parallel cavity of a pulsed, nearly single-mode KGW:Nd pump laser. We used a KTP crystal as the nonlinear medium for the OPO. We have shown that the intracavity OPO has the higher lasing efficiency. We have observed that the distribution of nonlinear losses introduced by the intracavity OPO, nonuniform over the cavity cross section, leads to an increase in the diameter and divergence of the radiation beam from the pump laser and a dependence of its temporal lasing dynamics on the transverse beam coordinate. We propose a physical model qualitatively explaining the spatial and temporal lasing dynamics of a radiation source with an intracavity OPO. Both OPO versions generate beams of radiation with about the same divergence. When the KGW:Nd laser has an electrical pumping energy of 7.3 J and a cavity length of 77 cm, the intracavity OPO and the extracavity OPO emit pulses with energies of 14.5 mJ and 12.0 mJ and duration 18 nsec and 13 nsec respectively. The divergence of the eye-safe radiation (λ = 1.578 μm) at 86.5% of the total pulse energy is no greater than 5.5 mrad for an OPO output beam diameter of = 2 mm. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 4, pp. 535–543, July–August, 2006.     

Compact, high-pulse-energy, picosecond optical parametric oscillator

We report a high-energy optical parametric oscillator (OPO) synchronously pumped by a 7.19 MHz, Yb:fiber-amplified, picosecond, gain-switched laser diode. The 42-m-long ring cavity maintains a compact design through the use of an intracavity optical fiber. The periodically poled MgO-doped LiNbO(3) OPO provides output pulse energies as high as 0.49 μJ at 1.5 μm (signal) and 0.19 μJ at 3.6 μm (idler). Tunability from 1.5 to 1.7 μm and from 2.9 to 3.6 μm is demonstrated, and typical M(2) values of 1.5 × 1.3 and 2.8 × 1.9 are measured for the signal and idler, respectively, at high power.     

Theory of intracavity absorption spectroscopy with a singly resonant optical parametric oscillator

The suitability of a singly resonant optical parametric oscillator pumped by a one-mode field and oscillating simultaneously in several signal and idler modes, for intracavity absorption spectroscopic measurements is studied theoretically. For steadystate operation, the enhancement factor ξ indicating the increased detection sensitivity, is shown to be mainly determined by the ratio of the intensity in one of the signal modes to the intensity (per mode) due to parametric fluorescence. Hence, rather high values of ξ, say of order 10⁸ or more, might be attainable, at least in principle. For pulsed operation, on the other hand, a numerical analysis leads to the result that for realistic pulse durations only moderate values of ξ (smaller than some 10³) will be found. Paper given in parts at the 6th Vavilov-Conference on Nonlinear Optics, Novosibirsk, USSR, 1979.