Diode-pumped Q-switched and mode-locked Nd:Gd0.3Lu0.33Y0.37VO4 laser with EO modulator and single-walled carbon nanotube

By using both the single-walled carbon nanotube saturable absorber (SWCNT-SA) and the electro-optic (EO) modulator, the stably doubly Q-switched and mode-locked (QML) operation of Nd:Gd_0.3Lu_0.33Y_0.37VO₄ laser has been demonstrated. The QML laser characteristics such as the pulse width, single-pulse energy, etc., have been measured for different modulation frequencies of the EO modulator (f_e) and reflectivity (R) of output coupler. In comparison with the solely passively QML laser with SWCNT-SA, the experimental results show that the doubly QML laser can generate more stable and shorter pulses with higher pulse energy. At 9.24 W pump power, f_e=1 kHz and R=93.5%, the doubly QML laser has compressed the Q-switched envelope pulse width 88% and improved the mode-locked pulsed energy 55 times.     

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.     

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.     

Diode-pumped doubly passively Q-switched c-cut Nd:GdVO4 1.34 μm laser with V:YAG and Co:LMA saturable absorbers

By simultaneously using both V³⁺:YAG and Co:LMA saturable absorbers in the cavity, a diode-pumped doubly passively Q-switched c-cut Nd:GdVO₄ laser at 1.34 μm is demonstrated for the first time. The average output power, the pulse width and the pulse repetition rate have been measured. The experimental results show that the doubly passively Q-switched laser can generate shorter pulse width with higher peak power in comparison to the singly passively Q-switched laser only with V³⁺:YAG or Co:LMA saturable absorber. At the pump power 13 W, the pulse width has been compressed 83% and the peak power has been improved 15 times, respectively.     

在相对论性激光-等离子体系统中初始物理参数对激光脉冲的影响

基于相对论性激光-等离子体动力学理论，研究了相对论性激光-等离子体系统中圆偏振入射脉冲激光和等离子体相互作用对激光脉冲宽度的影响. 具体分析了在不同初始物理参数下脉冲激光的脉冲宽度在等离子体传播过程中的变化情况，重点分析了激光脉冲在等离子中压缩. 计算结果表明增加入射激光的强度和入射脉冲宽度以及减小等离子体的初始密度，能够有效地实现脉冲宽度在等离子体中压缩；当激光脉冲的初始参数a₀=0.12和τ=70以及等离子体密度n₀=0.3时，脉冲宽度相对压缩T/τ接近于1/10，从而给出了激光压缩的理论优化参数. 关键词： 相对论性激光-等离子体 激光脉冲宽度 等离子体密度 自压缩     

Diode-pumped Q-switched and mode-locked Nd:LuVO4/KTP green laser with AO and Cr4+:YAG saturable absorber

A diode-pumped Q-switched and mode-locked (QML) Nd:LuVO₄/KTP green laser with acousto-optic modulator (AOM) and Cr⁴⁺:YAG saturable absorber is presented. By inserting an AOM into the laser cavity, the stability of the QML green laser pulse with AO and Cr⁴⁺:YAG is improved, the modulation depth is increased and the pulse width of Q-switched pulse envelope is significantly compressed in comparison with that of the singly passively QML green laser with Cr⁴⁺:YAG. The experimental results show that the peak power of the doubly QML green laser pulse is much higher than that of the singly passively QML green laser pulse.     

Improvement of stability and pulse energy in a diode-pumped dual-loss-modulated QML Nd:Lu0.2Y0.8VO4 laser with EO modulator and GaAs

The Q-switched and mode-locked (QML) performance in a diode-pumped Nd:Lu_0.2Y_0.8VO₄ laser with electro-optic (EO) modulator and GaAs saturaber absorber is investigated. In comparison with the solely passively QML laser with GaAs, the dual-loss-modulated QML laser with EO and GaAs can generate pulses with higher stability and shorter pulse width of Q-switched envelope, as well as higher pulse energy. At the repetition rate 1 kHz of EO, the pulse width of Q-switched pulse envelope has a compression of 89% and the pulse energy has an improvement of 24 times. The QML laser characteristics such as the pulse width, pulse peak power etc. have been measured for different small-signal transmittance (T₀) of GaAs, different reflectivity (R) of output coupler and modulation frequencies of the EO modulator (f_e). The highest peak power and the shortest pulse width of mode-locked pulses are obtained at f_e = 1 kHz, R = 90% and T₀ = 92.6%. By considering the influences of EO modulator, a developed rate equation model for the dual-loss-modulated QML laser with EO modulator and GaAs is proposed. The numerical solutions of the equations are in good agreement with the experimental results.     

Passive stabilization of a passively mode-locked Nd:GdVO4 laser by inverse saturable absorption

A diode-pumped Nd:GdVO₄ laser mode-locked by a semiconductor saturable absorber and output coupler (SESAOC) is passively stabilized to suppress Q-switched mode-locking. A phase mismatched BIBO second-harmonic generation (SHG) crystal is used for passive stabilization. The continuous wave mode-locking (CWML) threshold is reduced and the pulse width is compressed. The pulse width is 6.5 ps as measured at the repetition rate of 128 MHz.     

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.     

Temporal characteristics of picosecond stimulated Raman scattering in oxide crystals

The temporal characteristics of stimulated Raman scattering (SRS) under 22-ps laser excitation were studied in eight oxide crystals with a T ₂ optical-phonon dephasing time variable by up to two orders of magnitude. The measured SRS pulse width was shortened from 13.8 ps for Ba(NO₃)₂ (T ₂ = 26.5 ps) to 4 ps for the LiNbO₃ (T ₂ = 0.38 ps) crystal. The dependence of SRS pulse width on the dephasing time was analyzed in the framework of the known SRS theory.     

Diode-pumped doubly Q-switched Nd:Lu0.33Y0.37Gd0.3VO4 laser with an electro-optic modulator and a single-walled carbon nanotube saturable absorber

By simultaneously using an electro-optic (EO) modulator and a single-walled carbon nanotube saturable absorber (SWCNT-SA) in the cavity, a diode-pumped doubly Q-switched Nd:Lu_0.33Y_0.37Gd_0.3VO₄ (Nd:LuYGdVO₄) laser is demonstrated. At the incident pump power 11.43 W and f=2 kHz, the minimum pulse width 17.6 ns and the maximum pulse peak power 19,886 W can be obtained. The experimental results show that this doubly Q-switched Nd:LuYGdVO₄ laser can generate shorter pulse width and higher peak power compared to the singly Q-switched Nd:LuYGdVO₄ laser with only EO or SWCNT-SA.     

Doubly <Emphasis Type="Italic">Q</Emphasis>-Switched Nd:YAG Ceramic Laser

Using simultaneously both an acousto-optic (AO) modulator and a Cr⁴⁺:YAG saturable absorber in the cavity, we demonstrate for the first time the performance of a diode-pumped doubly Q-switched Nd:YAG ceramic laser. In contrast to purely acousto-optic Q-switched laser, this doubly Q-switched laser can generate shorter and more symmetric pulses. At an absorbed pump power of 10 W and a repetition rate of 20 kHz, the pulse width is compressed to 30 and 25 ns, respectively.     

Pulse compression in AO Q-switched diode-pumped Nd:GdVO4 laser with Cr4+:YAG saturable absorber

By simultaneously using both an acoustic-optic (AO) modulator and a Cr⁴⁺:YAG saturable absorber in the cavity, for the first time, a diode-pumped doubly Q-switched Nd:GdVO₄ laser has been realized. The pulse duration is obviously compressed in contrast to the actively acoustic-optic Q-switched laser. By considering the Gaussian transversal distribution of the intracavity photon density and the longitudinal distribution of the photon density along the cavity axis as well as the influence of turnoff time of the acoustic-optic (AO) Q-switch, we provide the coupled rate equations for a diode-pumped doubly Q-switched Nd:GdVO₄ laser with both an acoustic-optic (AO) modulator and a Cr⁴⁺:YAG saturable absorber. These coupled rate equations are solved numerically, and the dependence of pulse width, pulse energy and peak power on the incident pump power at different pulse repetition rates is obtained. The numerical solutions of equations agree well with the experimental results.This revised version was published online in August 2005 with a corrected cover date.     

High-energy sub-nanosecond optical pulse generation with a semiconductor laser diode for pulsed TOF laser ranging utilizing the single photon detection approach

Bulk and quantum well laser diodes with a large equivalent spot size of d _a /Γ _a  ≈ 3 µm and stripe width/cavity length of 30 µm/3 mm were realized and tested. They achieved a pulse energy and pulse length of the order of ~1 nJ and ~100 ps, respectively, with a peak pulse current of 6–8 A and a current pulse width of 1 ns. The 2D characteristics of the optical output power versus wavelength and time were also analyzed with a monochromator/streak camera set-up. The far-field characteristics were studied with respect to the time-homogeneity and energy distribution. The feasibility of a laser diode with a large equivalent spot size in single photon detection based laser ranging was demonstrated to a non-cooperative target at a distance of a few tens of meters.     

Diode-pumped Q-switched Nd:Y<Subscript>0.5</Subscript>Lu<Subscript>0.5</Subscript>VO<Subscript>4</Subscript> laser double-modulated with an acousto-optic modulator and Cr<Superscript>4+</Superscript>:YAG saturable absorber

A diode pumped Nd:Y_0.5Lu_0.5VO₄ pulse laser modulated with an acousto-optic (AO) Q-switcher and Cr⁴⁺:YAG saturable absorber is first demonstrated in this paper. The laser is shown to generate shorter pulse width than AO Q-switched laser alone, and have a higher peak power and single pulse energy than passively Q-switched laser with only Cr⁴⁺:YAG. A laser pulse width of 6.16 ns and a peak power of about 43.83 kW are achieved at the incident pumping power of 14.09 W.     

Eye-safe Raman laser based on BaTeMo2O9 crystal

An eye-safe Raman laser is realized with BaTeMo₂O₉ (BTM) nonlinear crystal for the first time. By using a diode-end-pumped acousto-optically Q-switched Nd:YVO₄ laser as the pumping source, the BTM crystal converts the fundamental laser at 1,342 nm to first-Stokes laser at 1,531 nm successfully. With an incident power of 10.8 W and a pulse repetition rate of 25 kHz, the average output power at 1,531 nm is obtained to be 0.83 W, corresponding to a diode-to-Stokes conversion efficiency of 7.7 %. The pulse width is 11 ns, and the peak power is 3.0 kW.     

Effect of nonlinear dispersion on pulse self-compression in a defocusing noble gas

Media with a negative Kerr index (n₂) offer an intriguing possibility to self-compress ultrashort laser pulses without the risk of spatial wave collapse. However, in the relevant frequency regions, the negative nonlinearity turns out to be highly dispersive as well. Here, we study the influence of nonlinear dispersion on the pulse self-compression in a defocusing xenon gas. Purely temporal (1+1)-dimensional investigations reveal and fully spatio-temporal simulations confirm that a temporal shift of high intensity zones of the compressed pulse due to the nonlinear dispersion is the main effect on the modulational instability (MI) mediated compression mechanism. In the special case of vanishing n₂ for the center frequency, pulse compression leading to the ejection of a soliton is examined, which cannot be explained by MI.     

Influences of diffusive reflection intensity and pulse shaping of ultrashort lasers on turbid media

The influences of the absorption μ_a, the scattering μ_s, and the anisotropy coefficient g on the optical properties of ultrashort pulse in turbid media has been simulated based on the diffusive approximation theory. The laser pulse intensity will be attenuated and the diffusive scattering pulse shape will be widened in the turbid media. Various medium parameters have different influences on the reflection of the laser pulse. The intensity loss of the diffusive reflection light is obtained when μ_a and μ_s are increased in turbid media. The pulse width of the diffusive reflection pulse is rapidly increased far away from the incident point and at the same time the pulse times that are delayed have been numerical simulated in the boundary conditions of semi-infinite homogenous media.     

Passively Q-switched laser performance of a diode-pump mixed Nd:Lu<Subscript>0.15</Subscript>Y<Subscript>0.85</Subscript>VO<Subscript>4</Subscript> crystal

A diode-pumped passively Q-switched Nd:Lu_0.15Y_0.85VO₄ laser with a GaAs output coupler is demonstrated. By using a mixed crystal Nd:Lu_0.15Y_0.85VO₄ as laser medium, the passively Q-switched laser can generate shorter pulse width with higher peak power in comparison with the passively Q-switched Nd:LuVO₄ or Nd:YVO₄ lasers under the same laser cavity. At the incident pump power 11.9 W, the minimum pulse width of 3.23 ns and the maximum peak power 1.67 kW can be obtained. The average output power and the pulse repetition rate of the laser are also measured. The experimental results show that the mixed crystal is a promising laser medium for shorter Q-switched pulse with higher peak power.     

Theoretical and experimental studies on passively Q-switched KTiOAsO4 optical parametric oscillator

A passively Q-switched intracavity optical parametric oscillator based on KTiOAsO₄ (KTA) crystal is studied theoretically and experimentally. The rate-equation-based theoretical model is established to describe the time evolutions of the population inversion density of the laser crystal, ground-state population density of the saturable absorber, fundamental photon density, signal photon density and the idler photon density. In the experiment, a laser diode-end pumped, passively Q-switched Nd:YAG/KTA IOPO with a Cr⁴⁺:YAG crystal as the saturable absorber is realized to verify this model. The characteristics including the output power, the pulse repetition rate, the pulse width and the beam quality were investigated for this OPO. The experimental results for the output power and the repetition rate agree with the theory well. And both results show that with same pumping level the idler pulse width is shorter than the signal one.