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.     

Diode-pumped passively Q-switched Nd:YVO4 green laser with a periodically poled KTP and Cr4+:YAG saturable absorber

A diode-pumped passively Q-switched Nd:YVO4 green laser with a periodically poled KTP and Cr4+:YAG saturable absorber is realized. The dependences of pulse repetition rate, pulse energy, pulse width, and peak power on incident pump power are measured for the generated green-light pulses. A rate-equation model is introduced to theoretically analyze the results obtained in the experiment, in which the spatial distribution of the intracavity photon density is taken into account. The numerical solutions of the rate equations agree with the experimental results.     

Diode-end-pumped passively Q-switched Nd:YAG crystal laser with V:YAG saturable absorber at 1319 and 1338 nm

A diode-end-pumped passively Q-switched Nd:YAG laser with a V:YAG saturable absorber emitting at 1319 and 1338?nm was demonstrated for the first time. A maximum output power of 286?mW was obtained with minimum pulse duration of 13.2?ns and the highest repetition rate was 15?kHz under an incident pump power of 7.7?W. The calculated highest peak power and pulse energy were 2.1?kW and 29?μJ, respectively.     

Laser-diode-pumped passively Q-switched Nd:YVO4 green laser with periodically poled KTP and GaAs saturable absorber

A laser-diode-pumped passively Q-switched Nd:YVO₄ green laser with periodically poled KTP (PPKTP) and GaAs saturable absorber has been realized. The dependences of pulse repetition rate, pulse energy, pulse width and peak power on incident pump power for the generated-green-light pulses are measured. At the maximum incident pump power of 4.1 W, the maximum average output power of 113 mW is obtained, corresponding to an optical conversion efficiency of 2.8%. At the same pump power, stable green laser pulses of duration of 44.6 ns and energy of 0.28 µJ are generated at a repetition rate of 403.4 kHz. The coupling wave rate equations for a passively Q-switched laser are also given and the numerical solutions agree with the experimental results.     

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.     

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%.     

Laser-diode pumped passively Q-switched Nd3+:NaY(WO4)2 laser with Cr4+:YAG saturable absorber

A laser-diode pumped passively Q-switched new type crystal Nd³⁺:NaY(WO₄)₂ (known as Nd:NYW) laser with Cr⁴⁺:YAG saturable absorber has been realized. The dependence of pulse repetition rate, pulse energy, pulse width, and peak power on pump power for different small-signal transmission 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.     

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%.     

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.     

Polarization-resolved study of diode-pumped passively Q-switched Nd:GdVO4 lasers

By using the natural birefringence of an a-cut Nd:GdVO(4) crystal, we experimentally investigate laser operation under different light polarizations (pi- and sigma-polarized emissions) and compare their performance. The laser performance is further compared with a diode-pumped c-cut Nd:GdVO(4) laser of the same parameters. We show experimentally that the c-cut Nd:GdVO(4) laser could have good passively Q-switched performance in a low-pump-power region but is influenced by other intrinsic laser effects, such as the thermally induced cavity losses; its performance is severely degraded under high pump power. The best passively Q-switched performance obtained in our experiments is from the a-cut pi-polarized laser, which gives the narrowest pulse of 5.4 ns with the highest peak power of 20 kW. Our experimental results show that, to achieve the best performance of the passively Q-switched laser operation, an overall consideration of laser parameters is important.     

Passively Q-switched Nd:YVO(4) laser with a Cr(4+):YAG crystal saturable absorber

We demonstrate, for the first time as far as we know, a passively Q-switched operation of a Nd:YVO(4) laser in which a Cr(4+):YAG crystal and a laser-diode bar are used as the saturable absorber and the pump source, respectively. Stable laser pulses as short as 28 ns with 20-muJ energy can be generated with this laser, which has the advantages of simplicity, high efficiency, and good long-term stability.     

Diode-pumped passively mode-locked Nd:YAG laser at 1338 nm with a semiconductor saturable absorber mirror

We demonstrate a diode-end-pumped passively mode-locked 1338 nm Nd:YAG laser with a semiconductor saturable absorber mirror. At the absorbed pump power of 8.89 W, an average output power of 1.12 W was obtained with a slope efficiency of 14%. The pulse width was 22.4 ps with a repetition rate of 63.9 MHz, corresponding to a peak power of 782 W. In addition, the bandwidth of the mode-locking spectrum is as narrow as 20.44 GHz, which shows the potential application in long-distance ranging and fiber information transmission because of the low dispersion of these ultrashort pulses.     

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.     

Passively Q-switched Nd:YVO4 waveguide laser using graphene as a saturable absorber

We report on passively Q-switched lasers in femtosecond laser written waveguide in Nd:YVO₄ crystal. Using graphene as a saturable absorber, passively Q-switched waveguide laser operations are achieved along both TE and TM polarizations with single modal profiles. Furthermore, all-angle linear light pump was utilized to investigate the thorough information of the polarization effects of the laser, showing that the optimum polarization for laser generation is TE. The maximum average output power is estimated to be 129 mW with 12.2% slope efficiency, corresponding to single-pulse energy of 8.1 nJ, pulse duration of 25.0 ns and repetition rate of 16.3 MHz.     

Watt-level Q-switched Nd:LuVO4 laser based on a graphene oxide saturable absorber

The demonstration is reported of a diode-pumped passively Q-switched Nd:LuVO₄ laser at 1064 nm using a transmission-type graphene oxide as the saturable absorber. The graphene oxide saturable absorber with a modulation depth of 10% was fabricated using a vertical evaporation method. With a pump of 11.5 W, a maximum output power of 1.353 W was obtained with 186-ns pulse duration and 336.7-kHz repetition rate, corresponding to a maximum pulse energy of 4 μJ per pulse.     

Diode-pumped doubly Q-switched mode-locked YVO4/Nd:YVO4/KTP green laser with AO and GaAs saturable absorber

By using both acousto-optic modulator and GaAs saturable absorber, a diode-pumped Q-switched and mode-locked(QML) YVO₄/Nd:YVO₄/KTP green laser is presented. The experimental results show that the doubly QML YVO₄/Nd:YVO₄/KTP green laser has good stability and nearly 100% modulation depth. The average output power and the pulse width of the Q-switched envelope have been measured. The mode-locked pulse inside the Q-switched envelope has a repetition rate of 137 MHz and its pulse width is estimated to be about 280 ps. By using a hyperbolic secant square function and considering the Gaussian distribution of the intracavity photon density, the coupled equations for diode-pumped dual-loss-modulated QML green laser is given and the numerical solutions of the equations are in good agreement with the experimental results.     

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.     

Beam-quality improvement of a passively Q-switched Nd:YAG laser with a core-doped rod

We present experimental results that demonstrate the great efficiency of a core-doped Nd:YAG rod (a hexagonal Nd:YAG core surrounded by undoped YAG) in producing high output power and excellent beam quality. An additional improvement in beam quality is clearly observed when the core-doped rod is used in combination with a LiF:F(2)(-) crystal, which acts as a passive Q-switching element. This improvement is quantified by beam-propagation factors as low as M(2) approximately = at a maximum average output power of 9 W. We show that transversally pumped core-doped rods with the addition of LiF:F(2)(-) crystals fulfill the requirements for high-beam-quality, scalable, compact all-solid-state lasers in passively Q-switched operation.     

Wide-band,passively Q-switched Yb- and Tm-doped fibre laser using WSSe saturable absorber

A wide-band, passively Q-switched fibre lasers based on ytterbium- and thulium-doped fibre gain medium are proposed and demonstrated. The lasers employ a transition metal dichalcogenide, tungsten sulphoselenide as a saturable absorber (SA) which is prepared by mechanical exfoliation technique. By integrating the SA in the laser cavities, self-starting Q-switched at 1038 and 1982?nm are obtained. The generated pulses exhibit a microsecond pulse duration with few kilohertz repetition rate. The proposed SA has high potential as a new material to cater to the needs of various scientific, industrial and biomedical applications.