Eye-safe radiation source based on an optical parametric oscillator

We have studied an optical parametric oscillator (OPO) with an unstable telescopic cavity, placed inside the cavity of an actively Q-switched multimode Nd³⁺:KGW pump laser. We used a KTP crystal as the nonlinear medium for the OPO. We have compared the emission characteristics of OPOs with unstable telescopic and planar cavities. We have established that compared with the planar cavity, the unstable cavity reduces the OPO beam divergence and improves the spatial distribution of the radiation energy in the far wave zone. Based on our investigations, we have designed a compact eye-safe (λ = 1.578 μm) laser source with natural cooling, emitting (for electrical pumping energy 7.3 J) pulses with pulse energy 22 mJ and pulse duration 6 nsec. The FWHM beam divergence for the source is no greater than 3.5 mrad. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 2, pp. 254–259, March–April, 2006.     

Intracavity Raman laser generating a third stokes component at 1.5 μm

The lasing properties of an intracavity Nd:KGW Raman laser which converts the multimode radiation of an Nd:KGW laser operating on the ⁴ F _3/2–⁴ I _11/2 transition into the third Stokes component at a wavelength of 1.5 μm are studied. The energy in the third Stokes component is found to increase essentially linearly with the electrical energy delivered to the flashlamp. Lasing at the third Stokes component begins in the central portion of the Nd:KGW crystal and then propagates to its boundaries. Reducing the geometric aperture of the multimode pump beam in the Raman crystal lowers the divergence of the Stokes emission. For a source pump energy of 6 J, the intracavity Raman laser emits 14.7 mJ pulses of duration 3–4 nsec which are safe to the eyes. The divergence of the Raman laser beam at a level of 86% of the total energy is ≈ 9 mrad.     

Travelling-wave 1.57-µm optical parametric oscillator driven by a pulsed multimode Nd3+:YAG laser

The generation properties of an optical parametric oscillator (OPO) with a three-mirror ring resonator have been investigated under conditions of a pulsed pump by multimode radiation from a Nd³⁺:YAG laser. KTP crystals were used as the OPO nonlinear medium. At pump energies up to 100 mJ, decreasing the diameter d of the Nd³⁺:YAG laser beam causes a decrease in OPO radiation divergence and an increase in the generation efficiency at λ = 1.571 μm despite a decrease in the differential efficiency. At d = 2.25 mm and a KTP crystal total length of 40 mm, the efficiency of the pump conversion to the signal-wave pulse reaches 36.5%. Based on the traveling-wave OPO, a compact, highly effective, eye-safe laser source radiating pulses of up to 35 mJ in energy, 11 nsec in duration, and 10 Hz in repetition rate at electrical pump energy of ≤ 8 J is developed. At the 86.5% level of the total pulse energy, the source-beam divergence does not exceed seven diffraction limits. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 4, pp. 516–523, July–August, 2008.     

Short pulse eye-safe laser with a stimulated Raman scattering self-conversion based on a Nd:KGW crystal

We present the results of a solid self-Raman laser based on a Nd:KGW crystal that is transversely pumped by laser diode bars. A beam of an eye-safe laser with a 31.8 mJ output energy and a 2.0 ns pulse width was obtained by applying a special s-polarized reflective resonator configuration in which the length of the Raman resonator was shorter than that of the fundamental radiation resonator. The eye-safe laser has the highest output energy and the shortest pulse width among the Nd:KGW lasers ever reported.     

Efficient sub-nanosecond intracavity optical parametric oscillator pumped with a passively Q-switched Nd:GdVO<Subscript>4</Subscript> laser

An efficient diode-pumped passively Q-switched Nd:GdVO₄/Cr⁴⁺:YAG laser was employed to generate a high-repetition-rate, high-peak-power eye-safe laser beam with an intracavity optical parametric oscillator (OPO) based on a KTP crystal. The conversion efficiency for the average power is 8.3% from pump diode input to OPO signal output and the slope efficiency is up to 10%. At an incident pump power of 14.5 W, the compact intracavity OPO cavity, operating at 46 kHz, produces average powers at 1571 nm up to 1.2 W with a pulse width as short as 700 ps. PACS 42.60.Gd; 42.65.Yj; 42.55.X     

Intracavity optical parametric oscillator at 1.5-7-μm wavelength pumped by passive Q-switched Nd:GdVO4 laser

A high-repetition-rate eye-safe optical parametric oscillator(OPO),using a non-critically phase-matched KTP crystal intracavity pumped by a passively Q-switched Nd:GdVO4/Cr4 :YAG laser,is experimentally demonstrated.The conversion efficiency for the average power is 7% from pump diode input to OPO signal output and the slope efficiency is up to 10.3%.With an incident pump power of 7.3 W.the compact intracavity OPO(IOPO)cavity,operating at 15 kHz,produces an average power of 0.57 W at 1570 nm with a pulse width as short as 6 ns.The peak power at 1570 nm is higher than 6.3 kW.     

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。     

Laser performance of <Emphasis Type="Italic">N</Emphasis><Subscript><Emphasis Type="Bold">g</Emphasis></Subscript>-cut flash-lamp pumped Nd:KGW at high repetition rates

A comparative study of the flash-lamp pumped laser performance of standard b-grown Nd:KGW and Nd:KGW grown for propagation along the optical axis N_g is presented. The results show that, in comparison with b-grown crystal, the N_g-grown Nd:KGW is very promising for use at high repetition flash-lamp pumping rates. With the same laser cavity configuration, the N_g-grown Nd:KGW can operate at an average flash-lamp input power of at least 1.4 kW, while the b-cut one ceases lasing at average flash-lamp input power of ∼0.5 kW. The reason for this is that the thermal lens induced in the N_g-oriented Nd:KGW rod under pump radiation is relatively weak, nearly spherical and positive, whereas the b-grown Nd:KGW rod acts as a quite weak positive lens for radiation with radial polarization, and as a much stronger negative lens for tangentially polarized radiation. PACS 42.60.Jf; 42.70.Hj     

An efficient intracavity-pumped KTP optical parametric oscillator at 1572 nm

We demonstrate an efficient and eye-safe wavelength intracavity optical parametric oscillator (OPO),based on a KTP crystal inside a Q-switched Nd:YVO4 laser end pumped by a fiber-coupled diode laser. Inthe acousto-optic Q-switched operation with the pulse repetition rate of 10 kHz, a 1572-nm eye-safe laser with the average power of 237 mW at the incident pump power of 5.64 W is obtained. Under the pulse repetition rate of 5 kHz, the signal light with pulse width of 2 ns and peak power of 18.5 kW is achieved.The conversion efficiency of the average power is 4.2% from pump diode to OPO signal output and thesignal pulse duration is about 13 times shorter than that of the depleted pump light.     

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.     

Diode-pumped passively Q-Switched intracavity OPO with a folded cavity configuration

We present in this report an efficient KTP-based intracavity optical parametric oscillator driven by a diode-pumped Nd:GdVO₄/Cr:YAG passively Q-switched laser. For the first time, a novel folded cavity configuration was employed to set the KTP and Cr:YAG crystals separately at different fundamental beam waists. Based on the ABCD-matrix theory and by taking the thermal lens effect into account, the laser cavity was well optimized to enhance the OPO performance. A diode pump threshold as low as 1.2 W and a maximum signal (1.57 μm) average output power up to 560 mW have been achieved. Efficient energy transfer in the IOPO leads to short pulse duration (1.8–2.6 ns) and high peak power (6.8 kW) output at 1.57 μm. Additionally, the correlation dynamics between the pump laser and the OPO was analyzed in detail.     

Compact eye-safe intracavity optical parametric oscillator with efficient pulse shortening

We report a compact eye-safe intracavity optical parametric oscillator (IOPO), driven by a diode end-pumped passively Q-switched Nd:YVO₄/Cr: YAG laser. At the incident diode pump power of 6.2 W and signal pulse repetition rate of 13 kHz, we obtain a minimum signal pulse duration as short as 1.3 ns, holding a pulse compressing factor of 17 with respect to that of the pump, and exhibiting an efficient pulse shortening mechanism. At the same time, the maximum average power of 110 mW and pulse energy of 8.5 μJ for the signal wave are also achieved. In addition, cavity dumping characteristics and the correlation dynamics between the laser and the OPO are qualitatively analyzed.     

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.     

Pulse-series 1.57 μm optical parametric oscillator pumped by a Q-switched Nd:YAG laser with a variable reflectivity mirror

A method of generating 1.57 μm pulse-series eye-safe laser based on optical parametric oscillator (OPO) was developed. The 1.57 μm pulse-series OPO was pumped by a Q-switched Nd:YAG laser with a variable reflectivity unstable resonator. Every pulse-series includes three micro-pulses, and the pulse repetition rates, pulse numbers and pulse intervals were adjustable. The maximum output energy of the 3-micro-pulse-series was 274 mJ. The optical-optical efficiency of the OPO was about 40%.     

Millijoule intracavity OPO driven by a passively Q-switched Nd:YVO<Subscript>4</Subscript> laser with AlGaInAs quantum-well saturable absorber

We originally demonstrate the use of an AlGaInAs periodic quantum-well absorber to achieve a quasi-continuous-wave (QCW) diode-pumped passively Q-switched Nd:YVO₄ laser with an intracavity optical parametric oscillator (OPO). With a diode-pumping energy of 35 mJ, the output pulse energy and the pulse width at 1573 nm are found to be 1.58 mJ and 26 ns, respectively. The pulse repetition rate can be up to 100 Hz with the overall OPO beam quality M² factor to be better than 1.5.     

Passive Q-switching of erbium glass laser by magnesium aluminosilicate sitall with cobalt ions

We have studied the radiation output parameters for an erbium glass laser, lasing at a wavelength of 1.54 μm, with passive Q-switching by means of a cobalt-containing magnesium aluminosilicate sitall compared with a saturable absorber based on a magnesium aluminum spinel crystal with cobalt ions. We have shown that the output characteristics of the laser emission when using sitall are not inferior to the analogous characteristics of a laser based on a spinel crystal, and are practically independent of the temperature of the saturable absorber in the range 0°C–80°C. The duration (energy) of the output pulses was 70 nsec (∼4 mJ), the energy dispersion of the radiation pulse relative to the average value was no greater than 3%, the beam divergence was 2.8 mrad, the laser beam quality factor was M² = 1.2. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 126–131, January–February, 2007.     

High-power eye-safe KTA-OPO driven by YVO4/Nd:YVO4 composite laser

We present a high-power 1.53 μm laser based on intracavity KTA-OPO driven by diode-end-pumped acousto-optical Q-switched YVO₄/Nd:YVO₄ composite. The composite crystal was utilized for reducing the thermal effect, and the mode mismatch compensating OPO cavity was designed for efficient OPO conversion. The output power of eye-safe laser at 1535 nm was up to 4.4 W with the pump power of 27 W, corresponding to a diode-to-signal conversion efficiency of 16.3%. To our knowledge, this is the highest output power in diode-end-pumped circumstances. In the experiment, the strong yellow light generated by Raman conversion and frequency doubling in the KTA crystal was observed.     

Nd:KGW/KGW crystal: efficient medium for continuous-wave intracavity Raman generation

Diode pumped continuous-wave intracavity Raman conversion in a composite Nd:KGW/KGW crystal has been investigated. The use of a Nd:KGW/KGW crystal instead of the ordinary Nd:KGW crystal has made it possible to considerably decrease intracavity losses. A Raman threshold corresponding to a diode laser power of 230 mW and a quantum efficiency of conversion of diode laser radiation to the Stokes radiation of 22% have been obtained. PACS 42.55.Rz; 42.55.Xi; 42.55.Ye     

BiB_3O_6纳秒光参变振荡器

采用电光调Q脉冲Nd:YAG固体激光器的532 nm绿光作为抽运光源(10～13 ns,0～20 mJ),以Ⅱ类相位匹配(θ=57.5°Φ=0°)、尺寸为4 mmX 4 mm×12 mm的三硼酸铋晶体(BiB3O6)与一对1215 nm单谐振波长的平镜组成腔长为40 mm的谐振腔,构建了光参变振荡器的整个实验系统.系统将入射抽运光振荡产生1215 nm的信号光及946 nm的闲频光,结果显示,抽运阈值为9 mJ,最高耦合输出为2.57 mJ,抽运脉冲能量与信号脉冲能量的最高转换效率为14.59%.     

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.