Compact, Low Threshold Nd^3＋：YVO4 Self-Raman Laser at 1178 nm

A compact low-threshold Raman laser at 1178 nm is experimentally realized by using a diode-end-pumped actively Q-switched Nd^3＋ ：YVO4 self-Raman laser. The threshold is 370mW at a pulse repetition frequency of S kHz. The maximum Raman laser output is 182 m W with the pulse duration smaller than 20 ns at a pulse repetition frequency of 30kHz with 1.8 W incident power. The optical efficiency from the incident power to the Raman laser is 10% and the slope efficiency is 13.5%.     

High average power and short pulse duration continuous wave mode-locked Nd:GdVO<Subscript>4</Subscript> laser with a semiconductor absorber mirror

Passive mode locking of a solid-state Nd:GdVO₄ laser is demonstrated. The laser is mode locked by use of a semiconductor absorber mirror (SAM). A low Nd³⁺ doped Nd:GdVO₄ crystal is used to mitigate the thermal lens effect of the laser crystal at a high pump power. The maximum average output power is up to 6.5 W, and the pulse duration is as short as 6.2 ps. The optic-to-optic conversion efficiency is 32.5% and the repetition rate is about 110 MHz.     

Pulse compression in AO Q-switched diode-pumped Nd:GdVO4 laser with V3+:YAG saturable absorber

By simultaneously using both an acoustic-optic (AO) modulator and a V³⁺:YAG saturable absorber in the cavity, for the first time to our knowledge, a diode-pumped doubly Q-switched Nd:GdVO ₄ laser has been realized. The dependence of pulse width, pulse energy and peak power on the incident pump power at determinate pulse repetition rate are measured. Under the absorbed pump power of 8.59 W, the pulse temporal profile of the AO-switching with the pulse duration of 14.5 ns, the double Q-switching with pulse duration of 7.6 ns at 10 kHz, and the passive Q-switching with pulse duration of 22.3 ns are obtained. The pulse duration is obviously compressed in contrast to the purely actively AO Q-switched laser or the purely passively Q-switched laser with V³⁺:YAG.     

Linearly polarized intracavity passive Q-switched Yb-doped photonic crystal fibre laser

In this paper we report linearly polarized high average power passive Q-switched ytterbium-doped photonic crystal fibre laser with a Cr⁴⁺:YAG crystal as a saturable absorber. An average output power of 9.4 W with pulse duration of 64 ns and pulse repetition rate of 57.4 kHz with a slope efficiency of 52% was achieved. Measured polarization extinction ratio (PER) of the Q-switched laser output was 10.5 dB.     

Self pulsations and self Q-switching in Ho3+, Pr3+:ZBLAN fibre lasers at 2.87 μm

The temporal characteristics of the output of a single-clad Ho³⁺, Pr³⁺-co-doped ZBLAN fibre laser pumped by a Nd:YAG laser at 1064 nm has been found to exhibit a range of cw, self pulsation and self Q-switching output dynamics, dependent on the excitation and fibre conditions. An interpretation is considered based on stimulated Brillouin scattering and the effect of the excited state absorption (ESA). For long fibre (∼13 m) and for uni-directional pumping, the output was a continuous wave (cw), but for bi-directional pumping, a significant decrease in the stability of the output is observed and the output displayed well developed self pulsations. A train of self Q-switched pulses with mean pulse duration of 767 ns, a peak pulse power of about 2.8 W and an average power of 183 mW and with more than 80% pulse-to-pulse stability has been observed when pumped with 4.4 W into each end of the fibre. Self pulsation phenomena are also observed in unidirectional pumping for shorter fibre lengths of ∼9.2 m at high pump power and for 1.5 m fibre length at all pumps power. PACS 42.55.Wd; 42.60.Gd; 42.60.Mi     

Pulse compression in diode-pumped doubly Q-switched Nd:GdVO<Subscript>4</Subscript> laser with both V<Superscript>3+</Superscript>:YAG and Co<Superscript>2+</Superscript>:LMA saturable absorber

By simultaneously using both a V³⁺:YAG and a Co²⁺:LaMgAl₁₁O₁₉ saturable absorber in the cavity, for the first time to our knowledge, a diode-pumped doubly Q-switched Nd:GdVO₄ laser has been realized. The dependence of pulse width, pulse repetition rate, pulse energy and peak power on the incident pump power are measured. Under the absorbed pump power of 8.59 W, both the pulse temporal profile of the passive double-switching with the pulse width of 25.29 ns, and the passive single-switching just using V³⁺:YAG with pulse width of 30.46 ns are obtained. The pulse duration is partly compressed in contrast to the purely passively Q-switched laser with V³⁺:YAG.     

Dual wavelength operation in diode-end-pumped hybrid vanadate laser

Dual wavelength operation at 1062.8 nm and 1064.1 nm in a diode-pumped hybrid laser comprising of Nd³⁺-doped birefringent YVO₄ and GdVO₄ crystals is demonstrated. A detailed characterization of the laser is performed under CW and pulsed operation. Under Q-switching, 4 W of average power at 5 kHz repetition rate is obtained with 32 ns FWHM pulse duration corresponding to 25 kW of the peak power. The intensity and the polarization of the individual spectral components can be easily controlled by changing the relative gain and the relative orientation of the two crystals. The resulting pulsed dual-wavelength laser has the potential to be used as a source for generating terahertz radiation.     

>100-kW linearly polarized pulse fiber amplifier seeded by a compact efficient passively Q-switched Nd:YVO4 Laser

We thoroughly develop compact high-peak-power Nd:YVO₄/Cr⁴⁺:YAG passively Q-switched lasers (PQS) as the seed source of the fiber amplifier. We exploit a nearly hemispherical cavity to reach the second threshold criterion and systematically consider the thermal lensing effect and the mode-size matching in the overall optimization. Employing a Cr⁴⁺:YAG absorber with 70% initial transmission, we obtain a 50-kHz seed pulse train with the pulse duration of 4.8 ns and the pulse energy of 22 ??J at a pump power of 5.4 W. Injecting this seed laser into a polarization maintained Yb-doped fiber, the pulse energy and peak power at a pump power of 16 W are enhanced up to 178 ??J and 37 kW, respectively. We also use an absorber with 40% initial transmission to generate a 25 kHz pulse train with the pulse duration of 1.6 ns and the pulse energy of 36 ??J at a pump power of 5.4 W. With this seed laser, we find that the surface damage of the fiber limits the maximum pulse energy and peak power to be 192 ??J and 120 kW, respectively.     

Optical chaos and hysteresis in a laser-diode pumped Nd doped fibre laser

Modulated pumping of a Nd³⁺ doped silica monomode fibre laser has been investigated experimentally. For small modulation depths the laser exhibits a resonance at the relaxation oscillation frequency, providing pulses of a few microseconds duration at a repetition rate in the region of 10 kHz, dependent on the average pump level above threshold. As the pump modulation depth is increased, hysteresis is observed as a function of modulation frequency, along with optical bistability. For further increase in modulation depth, optical chaos and period doubling are observed. Gain-switching has also been demonstrated.     

Solid-state laser passively Q-switched in a new geometry

A new passive Q-switching geometry of a laser cavity has been proposed. In the proposed scheme, the volume of the passive Q-switch just partially overlaps the intracavity laser beam cross-section, leading, however, to the entire beam modulation. This technique was applied for passive Q-switching of a flash-lamp pumped multimode YAG:Nd³⁺ laser by LiF:F₂⁻ crystals. The giant pulse laser action threshold has been detected in the proposed geometry, and is lower than that in the scheme where the passive Q-switch operates in the traditional manner. Stable giant pulse oscillation of 1064 nm wavelength with a pulse duration of 24 ns, pulse energy of 450 mJ, and pulse repetition rates of up to 100 Hz, have been obtained.     

Control of the pulse duration in one- and two-axis passively Q-switched solid-state lasers

We study theoretically and experimentally different methods to control the pulses emitted by solid-state lasers passively Q-switched by a saturable absorber. We explore one- and two-axis laser schemes allowing to control the pulse duration, which is ruled by the saturation powers of the transitions in the absorber and in the gain medium. In one-axis lasers, it is shown that the adjustment of the pump and laser beam sizes in the active medium and in the absorber provides an efficient means to control the pulse temporal shape and duration. Furthermore, a two-axis laser cavity supporting so-called forked-eigenstate operation permits to freely adjust the parts of the mode power which circulate in the gain medium and in the absorber. In this case, a lengthening of the pulse duration up to 500 ns is obtained with an increase of the average output power. The theoretical results obtained by using rate equations adapted to each cavity geometry are in close agreement with experiments performed on a diode-pumped Nd³⁺:YAG laser Q-switched by a Cr⁴⁺:YAG saturable absorber. The relevance of the different techniques to control the pulse durations in the framework of potential applications is discussed. Received 3 December 2001     

The optical limitation effect and features of luminescence kinetics in hybrid nanosystems with CdSe/ZnS quantum dots and organic agents

The optical limitation effect in three-component systems formed in colloidal solutions of semiconductor CdSe/ZnS quantum dots with participation of fullerene C₆₀ and perylene, has been experimentally investigated. The first and second harmonics of a YAG:Nd³⁺ laser operating in the single-shot mode with a pulse duration of 7 ns and laser pulses subjected to stimulated Brillouin scattering (SBS)-stimulated Raman scattering (SRS) compression with a duration of about 20 ps near 560 nm have been used as radiation sources. It is shown that the optical limitation efficiency in the systems studied is determined by electron transfer. This is confirmed by the analysis of luminescence quenching.     

Narrow pulse width and high power passively Q-switched Nd3+:Gd3Ga5O12 laser with Cr4+:YAG saturable absorber

A compact, diode-pumped passively Q-switched Nd³⁺:Gd₃Ga₅O₁₂ (Nd:GGG) laser with Cr⁴⁺:YAG saturable absorber has been successfully demonstrated. Stable Q-switched pulses with pulse energy of 100 ??J and high peak power of 14 kW have been obtained. The pulse width was as short as 7 ns with low repetition rate of 10 kHz. The dependence of pulse width, pulse repetition rate, pulse energy and pulse peak power on pump power have been measured respectively. Experimental results reveal that the Nd:GGG crystal with Cr⁴⁺:YAG saturable absorber is suitable for narrow pulse width and high power passively Q-switched lasers.     

Explosive decomposition of PETN with nanoaluminum additives under the influence of pulsed laser radiation at different wavelengths

The results of measurements of the threshold of explosive decomposition of PETN with 0.1 wt % additives of aluminum nanoparticles under the action of the first and second harmonics of a YAG:Nd³⁺ laser with a pulse duration of 12 ns are presented. A comparison of experimental and theoretical results is performed. It is concluded that the absorption of radiation heats the nanoparticles to form chemical decomposition kernels in the vicinity of the hotspot, so that the initiation of explosive decomposition is not associated with optical breakdown of the sample.     

调Q脉冲保偏光纤激光器的研究

以808nm半导体激光器为抽运源,掺钕双包层保偏光纤为增益介质,对调Q脉冲保偏光纤激光器进行了理论分析和实验研究.利用TDS5104型示波器探测输出脉冲激光的波形,并用光谱分析仪得到输出脉冲激光的光谱图.利用F-P腔型,在1060nm处获得平均功率为2.55W的脉冲激光输出,重复频率为1kHz时,输出单脉冲能量为2.3mJ,峰值功率为4.7kW.改变腔型,把二色镜倾斜放置兼作输出镜,最终获得了平均功率为3.5W的偏振脉冲激光输出,重复频率为1kHz时,输出单脉冲能量为3.3mJ,脉冲宽度为184ns,其峰 关键词： 激光技术 光纤激光器 掺钕保偏光纤 调Q     

Nd:YVO4自受激拉曼激光器调Q锁模特性

利用Nd:YVO4激光晶体的自受激拉曼效应,结合Cr:YAG被动锁模技术和倍频技术,实现了结构紧凑的1176 nm和588 nm黄光锁模激光输出。激光器为LD端面泵浦,三镜折叠腔结构,并且采用了透过率为10%的输出镜。Nd:YVO4晶体长度为10 mm,Nd3+离子掺杂质量分数为0.2%,Cr:YAG晶体的初始透过率为67%。10 W激光泵浦时,1176 nm激光平均输出功率为123 mW,调Q包络宽度为6 ns,调Q包络内的锁模脉冲重复频率高达1 GHz。588.2 nm 黄光的平均输出功率为8 mW。     

Continuous-wave and Q-switched laser operation of Nd:Gd0.18Y0.82VO4 mixed crystal

Efficient continuous-wave (cw), passively Q-switched, and actively Q-switched laser operations are demonstrated with a mixed vanadate crystal of Nd:Gd_0.18Y_0.82VO₄ under diode pumping. In a cw operation, an output power of 8.25 W is obtained at a maximum available incident pump power (P_in) of 15 W, with a slope efficiency of 56%. Using a Cr⁴⁺:YAG crystal of initial transmission of 62% as the saturable absorber for Q-switching, an average output power of 3.05 W is generated at pulse repetition frequency (PRF) of 16.7 kHz when the laser is pumped with the same maximum P_in. The pulse energy, pulse duration, and peak power are 183.3 μJ, 6.0 ns, and 30.6 kW, respectively. When actively Q-switched by an acousto-optic modulator, the laser produces an average output power of 5.5 W at PRF of 30 kHz with 16.2 W of pump power incident upon the laser crystal. The pulse energy, duration, and peak power are measured to be 183 μJ, 10.5 ns, and 17.5 kW, respectively.     

CW and passive Q-switching of 1331-nm Nd:GGG laser with Co<Superscript>2+</Superscript>:LMA saturable absorber

In this paper, the output performances at 1331 nm in continuous-wave (CW) operation and the passive Q-switching regime of a Nd:Gd₃Ga₅O₁₂(Nd:GGG) laser crystal have been investigated under pumping with diode lasers. A maximum CW output power of 1.5 W was reached at an incident pump power of 7.5 W; the overall optical-to-optical efficiency and the slope efficiency with respect to the pump power were 21.5% and 19.4%, respectively. The passive Q-switching regime was achieved with Co²⁺:LaMgAl₁₁O₁₉ (Co²⁺:LMA) saturable absorber (SA) crystals. A maximum average output power of 183 mW was recorded with a Co²⁺:LMA SA with initial transmission T _i of 90%. The pulse energy was 18.7 μJ and the pulse duration was 26.1 ns, which correspond to a pulse peak power of 0.7 kW. With a Co²⁺:LMA SA with T _i=81%, the average power decreased to 131 mW. However, the pulse energy increased to 21.4 μJ, the pulse duration was 16.4 ns and the pulse peak power increased to 1.3 kW.     

掺钕保偏光纤放大器的研究

对掺钕双包层光纤放大器中抽运光和信号光沿光纤传播的功率分布进行了数值模拟,以808nm半导体激光器为抽运源,掺钕双包层保偏光纤为增益介质,对种子注入主振荡光纤放大器进行了理论分析和实验研究.利用实验室自制的皮秒锁模激光器为种子源,注入1064nm皮秒锁模脉冲,获得了稳定的放大脉冲.小信号时的放大倍数为300（增益为25dB）,获得了平均功率5W的皮秒脉冲.同时利用TDS5104型示波器探测信号光放大前后的波形,并用光谱分析仪得到输出脉冲激光的光谱图. 关键词： 光纤放大器 掺钕保偏光纤 种子注入 反向抽运     

High repetition rate passively Q-switched diode-pumped Nd:YVO4 laser

We demonstrated an efficient and compact, diode-pumped passively Q-switched Nd:YVO₄ laser operation at 1.064 μm wavelength with high repetition rate, using Cr⁴⁺:YAG as saturable absorber, formed with a simple flat–flat resonator. The maximum CW output power of 4.05 W was obtained at the incident pump power of 8 W. For Q-switched operation, the maximum average output power was measured to be 1.4 W with the corresponding repetition rate of 200 kHz, the pulse width of 60 ns when the initial transmission of Cr⁴⁺:YAG crystal was 85%. The shortest pulse width of 12 ns, the largest pulse energy of 36 μJ and the highest peak power of 3 kW were obtained when the Cr⁴⁺:YAG crystal with an initial transmission of 60% was used.