YAG Saturable Absorber Research Articles

The effects of thermalization on the performance of passively Q-switched IC-OPOs

In this paper, we report a new model for passively Q-switched intracavity optical parametric oscillators (IC-OPOs), using Cr:YAG as a Q-switch crystal. The model considers the effects of thermalization in the Nd:YAG laser crystal, excited state absorption in the Cr:YAG saturable absorber, nonlinear loss due to pump depletion in the nonlinear crystal, the thermal lens effect and the mode overlap of the fields within the nonlinear crystal. The calculated pulse width for the 1,064 nm pump light was 6.2 ns compared to the experimental result of 6 ns, while the signal wave was calculated to have a pulse width of 1.75 ns compared to the experimental result of 2 ns. The model is shown to accurately calculate both the temporal and output power characteristics of the IC-OPO, which has not been previously reported to the best of our knowledge.

Initial Transmission Influence on Saturable Absorber Absorption Activity of Passive Q-Switching Erbium -Doped Fiber Laser System

The initial transmission effect on the activity of Cr+4: YAG saturable absorber with Er +3 doped fiber laser was investigated. Software computer program was built in this study for solving the rate equations model by Rung - Kutta –Fehlberg numerical method. The study reported that the absorption activity of ground state of saturable absorber decreases with the decreasing of the initial transmission, while the activity absorption of excited state begins to increase. Moreover, the total absorption activity of saturable absorber also decreases with the decreasing of the initial transmission.

Electron spin resonance study of an annealed Cr,Mg:YAG epitaxial saturable absorber

We have demonstrated the use of electron spin resonance (ESR) spectroscopy to observe the influence of high-temperature annealing in an oxidizing atmosphere on Cr3+ ion concentration changes in an epitaxial Cr,Mg:YAG saturable absorber. For this purpose, a set of samples of epitaxial Cr,Mg:YAG/YAG structures differing in both the concentration of Cr and Mg ions and the concentrations ratio of these ions have been synthesized using liquid phase epitaxy. The X-ray diffraction analysis and optical transmission spectra measurements were performed to characterize the obtained layers. The usefulness of the ESR technique for monitoring certain high-temperature induced changes in epitaxial Cr,Mg:YAG absorber has been verified.

Compact Nd:YAP/V:YAG nanosecond pulse generator at 1342 nm

A compact Q-switched laser with a separate Nd:YAP gain part and V:YAG saturable absorber was designed and constructed. The use of a Nd:YAP gain crystal may have certain advantages, such as polarization and wavelength stability, over the more common Nd:YAG active medium. Constructed Nd:YAP/V:YAG compact laser provides linearly polarized radiation at a wavelength of 1342 nm. Stable pulses 12 ns long with energy up to almost 0.2 mJ were generated. This laser system could serve as an eye-safe radiation source of long-range high-resolution LIDAR for autonomous vehicle control.

Continuous-wave and passively Q-switched pulse Yb:Ca3TaGa3Si2O14 lasers at 1.0 µm

Diode-pumped continuous-wave and passively Q-switched pulse Yb:Ca3TaGa3Si2O14 lasers are reported. At an absorbed pump power of 5.4 W, a 1046.4 nm continuous-wave laser with an output power of 3.24 W and a slope efficiency of 63.4% was obtained. When a Cr4+:YAG saturable absorber with an initial transmission of 95% was used, a 1015.2 nm passively Q-switched pulse laser with a repetition frequency of 5.43 kHz, energy of about 73.6 µJ, duration of 35 ns, and peak output power of 2.1 kW was demonstrated.

Dual-loss-modulated Q-switched YVO4/Nd:YVO4 laser based on both Bi2Se3 and Cr4+:YAG

A dual-loss-modulated Q-switched laser at 1.06 µm is investigated. Bi2Se3 and Cr4+:YAG saturable absorber were simultaneously inserted into a laser cavity and used to study output characteristics of Q-switched laser at 1.06 µm. The obtained shortest pulse width, repetition rate and maximum single pulse energy were 240 ns, 140 kHz, and 2.57 μJ, respectively. Compared with those obtained in Q-switched laser with single Bi2Se3 SA, the pulse width is compressed by 70% and peak power increases 3.3 times. The results show that Bi2Se3 is a promising material for all-solid-state Q-switched laser and dual-loss-modulated technique is an effective method to optimize the output characteristics of Q-switched laser with two-dimensional materials.

Continuous-wave and passively Q-switched pulse 1060 nm Nd:GdPO4 lasers

1060 nm continuous-wave and passively Q-switched pulse lasers were demonstrated in a 3.5-mm-thick X-cut Nd:GdPO4 crystal. At an absorbed pump power of 1.91 W, a 1060 nm continuous-wave laser with a maximum output power of 0.72 W and a slope efficiency of 42% was realized. When a Cr4+:YAG saturable absorber with an initial transmission of 85% was used, a passively Q-switched pulse laser with repetition frequency of 6.7 kHz, pulse energy of about 19 µJ, pulse duration of 58 ns, and peak power of 0.33 kW was obtained in a plano-concave cavity with a length of 95 mm and an absorbed pump power of 1.91 W. For a plano-plano cavity with a length of 9 mm and the same pump power, a pulse laser with repetition frequency of 7.2 kHz, pulse energy of about 14.1 µJ, pulse duration of 4.1 ns and peak power of 3.4 kW was obtained.

Wavelength-switchable 9.5 GHz graphene mode-locked waveguide laser

A multi-wavelength compact ultrafast laser based on a single-mode waveguide inscribed in Nd:YAG and graphene saturable absorber is developed. By changing the pump parameters, we demonstrate single-, dual- and multi- wavelength mode-locking regimes. Accurate control of intracavity losses provides stable CW passive mode-locking at a wavelength of 1064 nm and dual-wavelength mode-locking at 1061 and 1064 nm with a pulse repetition rate of 9.5 GHz.

Advances in All-Solid-State Passively Q-Switched Lasers Based on Cr4+:YAG Saturable Absorber

All-solid-state passively Q-switched lasers have advantages that include simple structure, high peak power, and short sub-nanosecond pulse width. Potentially, these lasers can be applied in multiple settings, such as in miniature light sources, laser medical treatment, remote sensing, and precision processing. Cr4+:YAG crystal is an ideal Q-switch material for all-solid-state passively Q-switched lasers owing to its high thermal conductivity, low saturation light intensity, and high damage threshold. This study summarizes the research progress on all-solid-state passively Q-switched lasers that use Cr4+:YAG crystal as a saturable absorber and discusses further prospects for the development and application of such lasers.

Diode-pumped bifunctional Nd:LGSB laser passively Q-switched by a Cr4+:YAG saturable absorber

We report on the output performances of a fiber-coupled diode pumped Nd:LGSB laser passively Q-switched by a Cr4+:YAG saturable absorber (SA), with emissions at 1.06-μm near-infrared wavelength, as well as at 0.53-μm visible green spectrum through the self-frequency doubling process. The 2.3-at.% Nd:LGSB crystal delivered 1.43 W continuous-wave power at 1.06 μm with an overall optical-to-optical efficiency (with respect to the absorbed pump power) of 0.50. Green light with 3.3-mW power was emitted in a free-generation regime at 1.95-W absorbed pump power. By employing a Cr4+:YAG SA crystal with initial transmission Ti = 0.89, laser pulses at 1.06 μm with 13.4-μJ energy at 17.1-kHz repetition rate were obtained for ∼1.8 W absorbed pump power. The green laser pulse energy was 0.21 μJ at a 37.7-kHz repetition rate. The pulse duration amounted to 4.8 ns for both wavelengths of emission, indicating pulse peak power of 2.8 kW and 43.7 W for operation at 1.06 μm and 0.53 μm, respectively.

Optimization of the Parameters of a Compact Laser Microchip Based on Nd:LSB with Cr:YAG Saturable Absorber

Two models of Nd:LSB microchip laser with Cr:YAG saturable absorber have been compared: the travelling wave model and the point model which is deduced from the first one by averaging of all characteristics over the resonator length. It has been shown that the point model is applicable only for a narrow range of laser parameters, in other cases the results of simulations based on these two models differ significantly.

Diode pumped cryogenic Yb:Lu3Al5O12 laser in continuous-wave and pulsed regime

We report on diode pumped cryogenic Yb: Lu3Al5O12 (LuAG) laser in the continuous-wave and pulsed regime. Under given experimental condition, we determined an optimum crystal temperature of 140 K for efficient laser operation. A maximum output power of 10.46 W with slope efficiency values of 48.6 and 67% with respect to incident and absorbed power respectively were achieved for an output coupler transmission of 40%. Yb:LuAG laser performed significantly better at 140 K with an output power 16 times and slope efficiency 7 times better than the values at 240 K. Self-starting passively Q-switched Yb:LuAG lasers were also characterized using Cr:YAG saturable absorbers with three different initial transmissions. A maximum pulse energy of 0.215 mJ and a peak power of 1.46 kW were obtained corresponding to the shortest pulse duration of 148 ns.

Continuous-wave mode-locked Tm:YAG laser with GaAs-based SESAM

Passive mode-locked laser operation at 2012 nm based on Tm:YAG and GaAs-based saturable absorber mirrors is demonstrated. Continuous-wave mode-locking performance was observed, resulting in a pulse width of 47.9 ps and 117 mW average output power at 97.7 MHz. The mode-locked laser exhibits an excellent stability with a remarkably high extinction ratio of 72 dB above carrier.

Sub-nanosecond pulse generation in a microchip Nd:La0.15Gd0.85VO4 laser

A sub-nanosecond microchip laser was constructed using a Nd:La0.15Gd0.85VO4 with Cr4+:YAG saturable absorber. A single 880 ps pulse was recorded under an incident pump power of 4.91 W, corresponding to a repetition rate of 35 kHz. When the incident pump power exceeded 5 W, the system transferred a single picosecond pulse train into 0.9/1.1 ns two pulse train forms. The average output power increased from 108 mW to 130 mW, corresponding to a peak power decrease from 3.5 kW to ~1.8 kW, which might be utilized for laser pulse self-calibrations in time-of-flight distance measurements.

Assessment of broad usability of a simple analytic model for passively Q-switched lasers with Cr:YAG saturable absorbers

Analytic approximations for key parameters of passively Q -switched (PQS) lasers, such as pulse energy and duration, were developed and widely tested in particular for microchip lasers with semiconductor saturable absorbers. However, the same approach can be readily extended to PQS lasers using Cr:YAG as the saturable absorber, including excited-state absorption (ESA) in the model. ESA causes a reduction of pulse energy and an increase in pulse duration. Interestingly, performances of many previously reported PQS lasers using Cr:YAG, from microchips to more powerful multi-millijoule lasers, are correctly predicted by this simple model. Unlike energy estimation, which is intrinsically robust, pulse width requires a more careful evaluation of the influence of the ratio (total linear loss)/(saturable loss) as a correction of the asymptotic result.

New high-power 1.1-μm light source: Diode-pumped continuous-wave and passively Q-switched Nd:LuYAG mixed crystal lasers

1.1-μm laser operation has been rarely investigated in laser materials other than Nd:YAG. In this report, using a diode end pumping geometry for providing a compact, low-threshold and high-efficiency system, continuous-wave and passively Q-switched Nd:LuYAG mixed crystal lasers at 1.1 μm were demonstrated, for the first time to our knowledge. In continuous-wave mode, a maximum output power up to 6.04 W was achieved at 1112.9 nm, 1116.64 nm and 1122.65 nm with a slope efficiency of 41.8%. Wavelength tuning was obtained from 1112.05 nm to 1123.17 nm discontinuously, which has never been demonstrated in Nd:YAG lasers. Moreover, using a Cr4+:YAG saturable absorber, stable passively Q-switched laser operation was also attained with a maximum average output power up to 1.71 W. The shortest pulse width was about 37.3 ns at repetition rate of about 21.52 kHz. The maximum pulse energy was about 79.3 μJ, which is believed to be the highest pulse energy that has ever been achieved in diode-end-pumped Nd3+ lasers at this specific 1.1 μm emission band.

A Doubly Q-switched Nd:GdYNbO4 Laser with Acousto-optical Q-switch and Cr4+:YAG Saturable Absorber

In this paper, we demonstrate for the first time a doubly Q-switched pulsed laser, using a novel Nd:Gd0.69Y0.3NbO4 mixed crystal and acousto-optical (AO) Q-switch and Cr4+:YAG saturable absorber. Compared to purely AO Q-switched lasers, the simultaneous use of AO Q-switches and Cr4+:YAG saturable absorbers provides the generation of a shorter pulse. We investigated in detail the output characteristics of pulsed Nd:Gd0.69Y0.3NbO4 lasers.

Laser performances of diode pumped Yb:Lu2O3 transparent ceramic at cryogenic temperatures

Continuous wave (CW) laser performances of 1 at.% Yb:Lu2O3 sesquioxide ceramic medium were studied under various cryogenic temperatures. Two different fiber coupled diode pump sources, one emitting around 975.7 nm volume Bragg grating (VBG) stabilized and another around 940 nm were used for comparison. Under the pump at 975.7 nm and 100 K cryogenic temperature, the laser yielded CW output power of 11.24 W for 20.3 W incident pump power, corresponding to an overall optical-to optical efficiency of 55%; the slope efficiency was 59%. For operation at room temperature, the output power was limited to 4.44 W whereas the slope efficiency was 27.5%. Optimum operation under 940 nm pump was obtained at 80 K. Under 940 nm pumping, Yb:Lu2O3 medium generated a CW output power of 3 W for 20 W; the slope efficiency was around 17%. The passive Q-switch operation was investigated with Cr4+:YAG saturable absorber (SA) crystal, employing the pump at 975.7 nm. Laser pulses with an energy of 0.35 mJ and a pulse duration of 116 ns at 26.1 kHz repetition rate were recorded with a Cr4+:YAG SA having 85% initial transmission.

Efficient diode pumped Yb:Y2O3 cryogenic laser

We report on continuous-wave and pulsed laser characteristics of Yb:Y2O3 transparent ceramic at cryogenic temperatures. A VBG stabilized pump diode emitting at 976 nm which matches with the zero-phonon line of the gain media was employed. At 100 K, a maximum continuous-wave output power of 12 W, around three times than that of 300 K and a slope efficiency of 54.4%, 2.4 times than that of 300 K was achieved using an output coupler transmission of 50% with respect to incident power. In passive Q-switched regime, using a Cr:YAG saturable absorber with an initial transmission of 85%, a maximum energy of 0.46 mJ per pulse was obtained with a peak power of 1.64 kW at a repetition rate of 19.6 kHz.

Nonuniform pumped passively Q-switched laser using Nd:YAG/Cr4+:YAG composite crystal with high-pulse energy

A Nd : YAG / Cr4 + : YAG composite crystal passively Q-switched laser with high-output pulse energy is studied both theoretically and experimentally. According to the characteristics of flash lamp pump, the rate equations of nonuniform pump are established. The pulse interval, pulse energy, and pulse width of the output pulse train are analyzed accurately by nonuniform pump. The experimental parameters are optimized by numerical simulation, with Cr4 + : YAG saturable absorber initial transmittance of 14%, output coupling mirror reflectivity of 30%, and cavity length of 9.7 cm. Under the same conditions, the maximum static energy is 954.34 mJ without Q-switch. An output pulse train with four pulses can be obtained at the same pump condition in experimental study. The four pulses energy are 156.5, 151, 149.74, and 145.76 mJ in turn with corresponding intervals of 20.81, 24.16, and 46.03 μs. The average pulse width is 5.72 ns. The Q-switch efficiency is 63.2%. The energy of the four pulses decreases, the pulse interval increases, and the pulse width is basically unchanged. The nonuniform pump theoretical and experimental results are in good agreement.