Passively Q-Switched Quasi-Continuous-Wave Diode-Pumped Intracavity Optical Parametric Oscillator at 1.57

We report on a passively Q-switched quasi-cw diode-pumped Nd:YAG including an intracavity optical parametric oscillator. The dynamics of this system is described by solving the coupled equations. The effect of the initial transmission of Cr⁴⁺:YAG saturable absorber on the signal wave operation is studied. Under optimum conditions, we achieve 2.3mJ energy at 1.57μm wavelength for 40Hz repetition rate. The peak power of the pulses amounts to 0.88MW with the pulse width of 2.6ns. When the Fresnel reflection losses of the filters are taken into account, the pulse energy would be higher than 2.3mJ. To the best of our knowledge, this is the highest pulse energy and peak power for such a type of single resonant quasi-cw diode pumped Nd:YAG/Cr⁴⁺:YAG IOPO laser.     

Diode-pumped passively Q-switched Nd:YVO_4 laser with GaAs saturable absorber

The intracavity photon density is assumed to be of Gaussian spatial distributions and its longitudinal variation is also considered in the rate equations for a laser diode (LD) end-pumped passively Q-switched Nd:YVO4 laser with GaAs saturable absorber. These space-dependent rate equations are solved numerically. The dependences of pulse width, pulse repetition rate, single-pulse energy, and peak power on incident pump power are obtained. In the experiment, the LD end-pumped passively Q-switched Nd:YVO4 laser with GaAs saturable absorber is realized and the experimental results are consistent with the numerical solutions.     

Experimental study of electro-optical-switched pulsed Nd:YAG laser

We report the specification of a compact and stable side diode-pumped Q-switched pulsed Nd:YAG laser. We experimentally study and compare the performance of the pulsed Nd:YAG laser in the free-running and Q-switched modes at different pulse repetition rates from 1 Hz to 100 Hz. The laser output energy is stabilized by using a special configuration of the optical resonator. In this laser, an unsymmetrical concave–concave resonator is used and this structure helps the mode volume to be nearly fixed when the pulse repetition rate is increased. According to the experimental results in the Q-switched operation, the laser output energy is nearly constant around 70 m J with an FWHM pulse width of 7 ns at100 Hz. The optical-to-optical conversion efficiency in the Q-switched regime is 17.5%.     

A Graphene-Based Passively Q-Switched Ho：YAG Laser

A 2.09-μm in-band pumped passively Q-switched Ho： YAG laser is demonstrated. Single layer graphene deposited on a quartz substrate is used as the saturable absorber for the Q-switched operation. The minimum pulse width of 2.11μs is obtained at an average output power of lOOmW, corresponding to a pulse repetition frequency of 57.1 kHz and the pulse energy of 1.75 μJ. The beam quality factors M^2 of the Q-switched laser are 1.18 and 1.22 in the horizontal and longitudinal direction, respectively. The optical-to-optical conversion efficiency of the passively Q-switched laser is 4.3%, which is the highest conversion efficiency in the 2 μm wavelength, to the best of our knowledge. It shows clearly that the Ho： YAG crystal is a potential gain medium in the 2 μm range for the graphene application.     

Numerical Modelling of QCW-Pumped Passively Q-Switched Nd：YAG Lasers with Cr^4＋：yAG as Saturable Absorber

Passively Q-switched quasi-continuous-wave （QCW） diode-pumped Nd：YAG laser with Cr^4＋ ：YAG as saturable absorber is numerically investigated by solving the coupled rate equations. The threshold pump rate for passively Q-switched QCW-pumped laser is derived. The effects of the pump rate and pump-pulse duration on the laser operation characteristics are studied theoretically. The pump power range can be estimated according to the number of output pulses. The numerical simulation results are in good agreement with the experimental results.     

High-peak-power passively Q-switched 1.3 μm Nd:YAG/V~(3+):YAG laser pumped by a pulsed laser diode

We demonstrate a high-pulse-energy, short-pulse-width passively Q-switched(PQS) Nd:YAG∕V3t:YAG laser at 1.3 μm, which is end-pumped by a pulsed laser diode. During the PQS regime, a maximum total output pulse energy of 3.3 m J is obtained under an absorbed pump pulse energy of 21.9 m J. Up to 400 μJ single-pulse energy is realized with the shortest pulse width of 6.16 ns and a pulse repetition frequency of 34.1 k Hz,corresponding to a peak power of 64.9 k W. The high-energy laser pulse is operated in the dual wavelengths of 1319 and 1338 nm, which is a potential laser source for THz generation.     

Analysis of tunable picosecond pulse generation from a distributed feedback Ti：sapphire laser

A distributed feedback Ti:sapphire laser (DFTL) pumped by a 532nm Q-switched pulse is proposed for the generation of tunable picosecond pulses. With coupled rate equation model, the temporal characteristics of DFTL are obtained. The numerical solutions show that the DFTL pulse with a 50-ps pulse duration and as much as 3.SmJ pulse energy can be obtained under 40-m J, 5-ns pulse pumping. The dependence of output pulse width on the laser crystal‘s length, pumping pulse duration, and pumping rate is also discussed in detail.     

Reply to Comment on ＇Q-switched Tm：YAG Laser Intracavity-Pumped by a 1064 nm Lasers

The essential goal of that paper （Chin. Phys. Lett. 26（2009） 124211） was to obtain a 2μm Tm：YAG laser with short pulse output. A Q-switched technique is used to realize the short pulse output in our laser system. The idea presented by Dr. Nieolaie Pavel is right. In our work, the directly Q-switched 2μm Tm：YAG pulse laser is not realized. As a matter of fact, the Q switch is used to directly switch the 1μm Nd：YAG laser.     

Pre-pumped passively Q-switched Nd:YAG/Cr:YAG microchip laser

A pre-pumped passively Q-switched Nd:YAG/Cr: YAG microchip laser is demonstrated with a peak power of 7.5 kW at pulse repetition rate of serveral kilohertzs. The full-width at half-maximum (FWHM) is 734 ps, and the pulse energy is 5.5 μJ with a fundamental spatial mode. In this system, the pre-pumped microchip laser of Nd: YAG/Cr: YAG wafer which is bonded through the thermal-bonding technique has achieved a time jitter value of 12 μs and a Q-switched amplitude instability of 1.26% (1δ) through the pre-pumped modulation technique.     

Modelling of passively Q-switched lasers with intracavity Raman conversion

We present a model of passively Q-switched Raman lasers by utilizing the rate equations. The intracavity fun-damental photon density, Raman photon density and the initial population-inversion density of the gain medium are assumed to be of Gaussian spatial distributions. These rate equations are normalized by introducing some synthetic parameters and solved numerically, and a group of general curves are generated. Prom these curves we can understand the dependence of the Raman laser pulse characteristics on the parameters about the pumping, the gain medium, the Raman medium and the resonator. An illustrative calculation for a passively Q-switched Nd^3＋：GdVO4 self-Raman laser is presented to demonstrate the usage of the curves and related formulas.[第一段]     

Optimization of passively Q-switched laser with V:YAG saturable absorber

By considering the Gaussian spatial distributions of the intracavity photon density and the initial population-inversion density, the coupled rate equations for a diode-pumped passively Q-switched laser with V³⁺:YAG saturable absorber are given. These coupled rate equations are solved numerically and the key parameters of an optimally coupled passively Q-switched laser with V³⁺:YAG at 1342 nm are determined. These key parameters include the parameters of the gain medium, the saturable absorber and the resonator, which can maximize the pulse energy of singly Q-switched pulse. The optimal calculations for a diode-pumped passively Q-switched a-Nd:GdVO₄ laser with V³⁺:YAG saturable absorber are presented to demonstrate the numerical simulation applicable.     

Optimization of passively Q-switched and mode-locked laser with Cr:YAG saturable absorber

By considering the Gaussian spatial distributions of the intracavity photon density and the initial population-inversion density, the coupled rate equations for a diode-pumped passively Q-switched and mode-locked (QML) laser with Cr⁴⁺:YAG saturable absorber are given. These coupled rate equations are solved numerically and the key parameters of an optimally coupled passively QML laser are determined for the first time. These key parameters include the parameters of the gain medium, the saturable absorber and the resonator, which can maximize the pulse energy of singly Q-switched envelope. The optimal calculations for a diode-pumped passively QML Nd:GdVO₄ laser with Cr⁴⁺:YAG saturable absorber are presented to demonstrate the numerical simulation applicable.     

Theoretical and experimental study of a diode-pumped doubly Q-switched Nd:GdVO4 1.34 μm laser with acousto-optic (AO) modulator and V:YAG saturable absorber

A diode-pumped doubly Q-switched c-cut Nd:GdVO₄ laser at 1.34 μm with acousto-optic (AO) modulator and V³⁺:YAG saturable absorber is demonstrated. This doubly Q-switched laser can generate shorter pulse width and higher peak power than the singly Q-switched laser only with an AO modulator or a V³⁺:YAG saturable absorber. By considering the thermal lens effect of the laser gain medium, the coupled rate equations for the doubly Q-switched laser at 1.34 μm under Gaussian approximation are given. The numerical solutions of the equations are in agreement with the experimental results.     

Passive Q-switching of a laser-diode-pumped intracavity-frequency-doubling Nd:Nd<Superscript>3+</Superscript>:NaY(WO<Subscript>4</Subscript>)<Subscript>2</Subscript>/KTP laser with Cr<Superscript>4+</Superscript>:YAG saturable absorber

Nd³⁺:NaY(WO₄)₂, known as Nd:NYW, is a new type crystal. By using laser-diode as pump source, a passive Q-switching of intracavity-frequency-doubling Nd:NYW/KTP laser has been realized with Cr⁴⁺:YAG saturable absorber. The dependence of pulse repetition rate, pulse energy, pulse width, and peak power on incident pump power for different small-signal transmissions of Cr⁴⁺:YAG are measured. The coupled rate equations are used to simulate the Q-switched process of laser, and the numerical solutions agree with the experimental results.     

Passive Q-switches for Nd:hosted Solid State Lasers

The currently available Nd:hosted lasers utilizing passive Q-switches: a plastic dye sheet, a LiF:F₂- color center crystal, a Cr⁴⁺:YAG crystal or a RG1000 colored glass filter have been investigated in detail and the results summarized for comparison purposes for the first time. We first briefly summarize our own and others’ past studies, and report on recent new results concerning the use of Cr⁴⁺:YAG crystals and RG1000 colored glass filters as Nd:hosted laser passive Q-switchings. We then investigate in detail solid state laser system design using the above four passive modulators. Typical interpretations are given based on characteristic features of the materials, such as their saturation intensity and relaxation times. The results are then explained via adequate equations derived with respect to the relevant physical parameters of the materials. The optical dersity selection of plastic dye sheet passive Q-switching for the Nd:YAG laser system design is verified quantitatively, and the slope efficiencies from plastic dye sheet passive Q-switched operation by single pulse and multiple pulse bursts are investigated. The multi-peak Q-switched pulse timing phenomena are presented as well. The outstanding annealability, long lifetime, inexpensiveness and high repetition rate operation of LiF:F₂- crystals are highly recommended.     

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.     

Diode-pumped doubly passively Q-switched Nd:LuVO4/KTP green laser with Cr:YAG and GaAs saturable absorbers

A diode-pumped doubly passively Q-switched intracavity-frequency-doubling Nd:LuVO₄/KTP green laser with Cr⁴⁺:YAG and GaAs saturable absorbers is demonstrated. This laser can generate the shorter pulse width with higher peak power compared with the singly passively Q-switched green laser with Cr⁴⁺:YAG or GaAs saturable absorber. The relations between the pulse symmetry and the ratio of the small-signal transmissions of two saturable absorbers are investigated. By reasonably choosing the small-signal transmissions of both saturable absorbers, the doubly passively Q-switched green laser can generate the much more symmetric pulse profile. The coupled rate equations are used to simulate the passively Q-switched process of the green laser by considering the Gaussian transversal and longitudinal distributions of the intracavity photon density. The numerical results of the equations are consistent with the experimental results.     

Theoretical investigation of feasibility of Yb:YAG as laser material for nanosecond pulse emission with large energies in the Joule range

The long fluorescence lifetime of the upper laser level of Yb:YAG seems to make it an attractive material for the realization of Q-switched pulses with large pulse energy. The consequences of the spectroscopic parameter set of Yb:YAG for the feasibility of a large pulse energy laser, which emits pulses with nanosecond duration, are addressed on the basis of a rate equation model. The rate equations are analytically solved and applied to the optical side pumping of Yb:YAG rods. The thermal population of the lower laser level and the saturation of the laser material are discussed in specific.     

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.     

The study of green laser performances by using composite crystals of different initial transmissions

This paper reported a passively Q-switched green laser of LD pumped linear cavity structure by using Nd:YAG/Cr⁴⁺:YAG composite crystal and the type II phase matching KTP crystal. The dependence of average output power, pulse width and pulse repetition rate on pump power at different initial transmissions of Cr⁴⁺:YAG were measured and analyzed. With Cr⁴⁺:YAG of 80% initial transmission, under pump power of 13.97 W, the output average power is up to 681 mW, with pulse width of 200 ns and pulse repetition rate of 9.1 kHz. The laser operates in a fundamental mode.