Analysis of a diode-pumped passively Q-switched Nd:GdVO4 self-stimulating Raman laser

This paper presents the theoretical and experimental results of a laser diode-pumped passively Q-switched Nd:GdVO₄ self-Raman laser in detail. In the experiment, by using two Cr⁴⁺:YAG crystals with different initial transmissions as the saturable absorber, using Nd:GdVO₄ as the gain medium and Raman medium simultaneously, the passively Q-switched operation of the Nd:GdVO₄ self-Raman laser at 1176 nm was investigated. The average power, pulse energy, pulse width and pulse repetition rate with respect to the incident pump power were measured. The obtained maximum output average power is 244.6 mW with respect to incident power of 5.7 W and the corresponding conversion efficiency is 4.3%. In the theoretical part, we used the rate equations to obtain the theoretical results. In the rate equations, the Gaussian distributions of the intracavity photon densities of the fundamental and Raman lasers and the initial population-inversion density were taken into account, and the ground-state population density of the saturable absorber at t = 0 is assumed to be uniform. The obtained theoretical results were in agreement with the experimental results on the whole.     

Optimization of the pulse-width of diode-pumped passively Q-switched mode-locked c-cut Nd:GdVO4 laser with a GaAs saturable absorber

By considering the single-photon absorption and two-photon absorption processes in the GaAs saturable absorber, the coupled rate equations for a diode-pumped passively Q-switched and mode-locked (QML) laser with GaAs coupler under Gaussian approximation are given. These rate equations are solved numerically. The key parameters of an optimally coupled passively QML laser with the shortest pulse-width envelope are determined. These key parameters include the parameters of the gain medium, the saturable absorber, and the resonator, which can minimize the pulse-width of a singly Q-switched envelope. Sample calculations for a diode-pumped passively Q-switched mode-locked c-cut Nd:GdVO(4) laser with a GaAs coupler are presented to demonstrate that the shortest pulse-width envelope can be obtained by selecting the optimal small-signal transmission of the saturable absorber and the reflectivity of the output mirror.     

Theoretical and experimental study on passive mode-locking composite Nd:GdVO4/Nd:GdVO4/Nd:GdVO4 lasers

Stable passive mode-locking multi-segment composite Nd:GdVO₄ lasers with a semiconductor saturable absorber mirror were demonstrated for the first time. For the composite crystals, the output power increased linearly with the increase of the incident pump power, showing excellent thermo-mechanical performances. While for the conventional crystal, power saturation was observed when the incident pump power exceeded 8.79 W. The maximum average output power of 1.465 W was achieved by Nd(0.1%):GdVO₄/Nd(0.5%):GdVO₄/Nd(1%):GdVO₄ composite crystal at an incident pump power of 9.28 W. The largest pulse energy of 14.90 nJ and the highest peak power of 0.53 kW with a pulse duration of 28.0 ps were also obtained by using the same composite crystal, revealing that the multi-segment composite crystal with a proper combination of Nd³⁺-doped concentrations could obtain the optimal laser performance.     

A highly efficient graphene oxide absorber for Q-switched Nd:GdVO4 lasers

We demonstrated that graphene oxide material could be used as a highly efficient saturable absorber for the Q-switched Nd:GdVO4 laser. A novel and low-cost graphene oxide (GO) absorber was fabricated by a vertical evaporation technique and high viscosity of polyvinyl alcohol (PVA) aqueous solution. A piece of GO/PVA absorber, a piece of round quartz, and an output coupler mirror were combined to be a sandwich structure passive component. Using such a structure, 104 ns pulses and 1.22 W average output power were obtained with the maximum pulse energy at 2 μJ and a slope efficiency of 17%.     

Control of the pulse width in a diode-pumped passively Q-switched Nd:GdVO4/KTP green laser with a Cr4+:YAG saturable absorber

Different techniques to control the pulse width of a diode-pumped passively Q-switched Nd:GdVO4/KTP green laser have been theoretically and experimentally studied. It is shown that, when we vary the positidns of the saturable absorber in the laser axis and the pump beam waist in the gain medium, we obtain an efficient means to control the pulse width. The experiments performed on a diode-pumped Nd:GdVO4/KTP green laser passively Q-switched by a Cr4+:YAG saturable absorber are consistent with the theoretical calculations obtained from the rate equation model, in which the intracavity photon density that is assumed to be the Gaussian spatial distribution, the longitudinal variation of the intracavity photon density, and the pump beam spatial distribution are also considered.     

Compact KTA-based intracavity optical parametric oscillator driven by a passively Q-switched Nd:GdVO4 laser

We present a compact and efficient KTA-based intracavity optical parametric oscillator (IOPO) driven by a diode-end-pumped Nd:GdVO(4)/Cr:YAG passively Q-switched laser. At the incident diode pump power of 9.2 W, signal (1.53 microm) and idler (3.47 microm) average output powers of up to 744 and 356 mW, respectively, have been obtained. The total (signal+idler) optical-to-optical conversion efficiency is as high as 12%. By using the knife-edge method, near-diffraction-limited signal and idler beams have been detected, and the M(2) factors are well within 1.2. In addition, based on the ABCD matrix theory, the impact of mode matching and the thermal lens effect on the OPO output have been analyzed.     

Comparison on performance of passively Q-switched laser properties of continuous-grown composite GdVO4/Nd:GdVO4 and YVO4/Nd:YVO4 crystals under direct pumping

The comparison on performance of passively Q-switched laser properties of continuous-grown composite GdVO(4)/Nd:GdVO(4) and YVO(4)/Nd:YVO(4) crystals under direct pumping to the emitting level was demonstrated. A Cr(4+):YAG crystal was used as saturable absorber. At an incident pump power of 10 W, the average output power, the pulse width, the repetition rate, the pulse energy, and the peak power for a GdVO(4)/Nd:GdVO(4) laser were 1.22 W, 48.1 ns, 121 kHz, 10.1 μJ, and 209.6 W, respectively. And for a YVO(4)/Nd:YVO(4) laser under the same conditions, these output characteristics were 1.26 W, 44.9 ns, 218 kHz, 5.8 μJ, and 128.7 W, respectively.     

Thermal tuning of laser pulse parameters in passively Q-switched Nd:YAG lasers

Modifying the output pulses of a passively Q-switched Nd:YAG laser, operating at 1064 nm, was realized by heating the laser crystal. With the demonstrated laser setups, a 100 K temperature rise led to a more than 50% increase in the pulse energy and a more than 10% decrease in the pulse length. This method offers an effective way to tune the output of the laser without mechanical adjustment or a change of components.     

Experimental and theoretical study of a laser-diode-pumped passively Q-switched intracavity-frequency-doubled Nd:GdVO4/KTP red laser with V:YAG saturable absorber

A laser-diode-pumped passively Q-switched intracavity-frequency-doubled Nd:GdVO4/KTP red laser with V:YAG saturable absorber is realized in a V-type resonator. The dependences of the pulse repetition rate, pulse width, single-pulse energy, and peak power on the incident pump power are measured and contrasted. By assuming the intracavity photon density and the initial population-inversion density to be Gaussian spatial distributions, the space-dependent rate equations of this laser are given. The numerical solutions of the rate equations are consistent with the experimental results. In order to optimize the described system, the variations of the pulse width, peak power, single-pulse energy, and laser efficiency with the initial transmission of the saturable absorber and the ratio of the laser beam radius to the pump beam radius are also calculated, respectively.     

InGaAs quantum-well saturable absorbers for a diode-pumped passively Q-switched Nd:YAG laser at 1123 nm

A low-loss semiconductor saturable absorber based on InGaAs quantum wells was developed for highly efficient Q switching of a diode-pumped Nd:YAG laser operating at 1123 nm. With an incident pump power of 16 W, an average output power of 3.1 W with a Q-switched pulse width of 77 ns at a pulse repetition rate of 100 kHz was obtained.     

Passive mode-locking of diode-pumped Nd:GdVO4 laser with carbon nanotube intracavity absorber

By using single-walled carbon nanotubes as the saturable absorber fabricated by a vertical evaporation method, passive mode-locking of a Nd:GdVO₄ laser was realized in a W-type folded cavity. The laser generated 8?ps pulses at a repetition rate of 81?MHz. At 10.4?W of the incident pump power, average output power of 1.22?W was achieved and the corresponding peak power and energy of a single pulse were 1.88?kW and 15?nJ, respectively.     

Fluorescence feedback control of an active Q-switched diode-pumped Nd:YVO4 laser

We have implemented active feedback control in a Q-switched diode-pumped Nd:YVO(4) laser by monitoring the fluorescence intensity from the laser crystal. When the initial inversion level indicated by the detected fluorescence has reached a predetermined value, Q switching is initiated. This scheme allowed us to vary the reproducibility of the output pulse peak power and pulse width. The novel active Q-switching approach can reduce the shot-to-shot variations of the output pulse peak power and the pulse width.     

Diode-pumped passively mode-locked multiwatt Nd:GdVO4 laser with a saturable Bragg reflector

We report a first demonstration, to our knowledge, of a cw passively mode-locked Nd:GdVO4 laser (k = 1063 nm). A relaxed saturable Bragg reflector was used. The laser generates pulses of 9.2 ps at a repetition rate of 119 MHz. As much as 5.4 W of average power was realized with a slope efficiency of 25.7%.     

Plate-shaped Yb:LuPO4 crystal for efficient CW and passively Q-switched microchip lasers

It is demonstrated that plate-shaped crystals of Yb:LuPO₄, which are grown from spontaneous nucleation by high-temperature solution method, can be utilized to make microchip lasers operating in continuous-wave (CW) or passively Q-switched mode. Efficient operation of such a microchip laser, which is built with a 0.3 mm thick crystal plate in a 2 mm long plane-parallel cavity, is realized at room temperature. With 2.37 W of pump power absorbed, 1.45 W of CW output power is generated with a slope efficiency of 73%. When passively Q-switched with a Cr⁴⁺:YAG crystal plate as saturable absorber, the laser produces a maximum pulsed output power of 0.53 W at 1013.3 nm, at a pulse repetition rate of 23.8 kHz, the resulting pulse energy, duration, and peak power are 22.3 μJ, 4.0 ns, and 5.6 kW, respectively.     

Holmium lasers passively Q-switched with PbS quantum-dot-doped glasses

PbS quantum-dot-doped glasses are demonstrated as saturable absorber Q-switches for 2 microm holmium lasers. Q-switched pulses from Ho3+:Y3Sc2Al3O12 and Ho3+:Y3Al5O12 lasers of 50 and 70 ns in duration, respectively, have been obtained demonstrating up to 13% of energy conversion efficiency from free-running to Q-switched output.     

Polarization control of a Q-switched, diode-pumped Nd:YAG laser

We describe control of the polarization state of a diode-pumped Nd:YAG laser that is Q switched with an acousto-optic modulator (AOM). One of two orthogonal linear polarization states can be made dominant, depending on the amount of loss introduced by the AOM. Heterodyne beating indicates that the two polarization states are of slightly different frequencies.     

Miniaturized, high-power diode-pumped, Q-switched Nd:YAG laser oscillator-amplifier

A miniaturized, passively Q-switched Nd:YAG laser oscillator-power amplifier is reported, which is axially pumped by a compact, fiber-coupled, high-power, quasi-cw diode laser module. The pumping intensity of the oscillator crystal can be adjusted independently of the pumping intensity of the amplifier. This ensures that the oscillator pulse enters the amplifier when its maximum population density is reached. Furthermore, pulse bursts can be generated with a definite, adjustable number of single pulses. Maximum pulse energies of 8.4?and 22?mJ were achieved for a single pulse and for a pulse burst, respectively, at a pumping power of 470?W. The pulse widths were 2?ns, whereas the beam quality corresponded to M2<1.5. The laser is appropriate for scaling the power to the 10?MW range. Operation by using a 100?m pumping fiber was demonstrated.     

Passively Q-switched mode-locking Nd:GdVO4 laser with a chemically reduced graphene oxide saturable absorber

A diode-pumped passively Q-switched mode-locking Nd:GdVO₄ laser using a chemically reduced graphene oxide saturable absorber was demonstrated. The repetition rate and pulse width of the Q-switching envelopes were 5.7 MHz and 100 ns, respectively, while those of the mode-locking pulses that were modulated in the Q-switching envelopes were 139 MHz and 10 ps. At the maximum pump power of 7 W, the average output power was 1.38 W, corresponding to a slope efficiency of 25%.     

Passively Q-switched ceramic Nd3+:YAG/Cr4+:YAG lasers

Passively Q-switched ceramic Nd3+:YAG lasers with ceramic Cr4+:YAG saturable absorbers are demonstrated. When the lasers are pumped by a 1-W cw laser diode, optical-optical efficiency as great as 22% is obtained with Cr4+:YAG of initial transmission ranging from 94% to 79%. The results are similar to those in their crystalline counterparts. The operation of Brewster's angle and the polarization state of the laser output are also investigated.     

Cost-effective low timing jitter passively Q-switched diode-pumped solid-state laser with composite pumping pulses

A novel scheme that combines gain switching with passive Q switching of a miniature diode-pumped solid-state laser is proposed and implemented. A composite pumping pulse, consisting of a long, low-intensity pulse and a following short, high-intensity pulse, is used to reduce the timing jitter. A greater-than-tenfold reduction in timing jitter is demonstrated.