Acousto-optic Q-switched Laser Research Articles

An LED-Side-Pumped Intracavity Frequency-Doubled Nd,Ce:YAG Laser Producing a 2W Q-Switched Red Beam

We report a high-average-power acousto-optic (AO) Q-switched intracavity frequency-doubled red laser based on a high-efficiency light-emitting-diode (LED) pumped two-rod Nd,Ce:YAG laser module. Under quasi-continuous wave operation conditions, a maximum output power of 1319.08 nm wavelength was achieved at 11.26 W at a repetition rate of 100 Hz, corresponding to a maximum optical efficiency of 13.9% and a slope efficiency of 17.9%. In the active Q-switched regime, the pulse energy of the laser was as high as 800 μJ at a repetition rate of 10 kHz with a pulse width of 1.5 μs. Under non-critical phase-matched KTP crystal conditions, an average power of 2.03 W of 658.66 nm through intracavity frequency-doubling was obtained at a repetition frequency of 10 kHz with a duration of 1.3 μs, and the M 2 factor was measured to be about 5.8. To the best of our knowledge, this is the highest average power of an LED-pumped AO Q-switched 1319 nm laser and intracavity frequency-doubled red laser reported to date.

High-energy acousto-optic Q-switched alexandrite laser with wavelength tunable fundamental and UV second harmonic generation

We investigate high-energy mJ-class diode-pumped acousto-optic (AO) Q-switched alexandrite lasers with broad tunability at both the fundamental near-IR wavelength range and second harmonic generation (SHG) in the UV wavelength range. An AO Q-switched alexandrite laser with continuous-wave diode-pumping has been operated at up to 10 kHz and producing pulse energy of 700 µJ at repetition rate of 1 kHz. With pulsed double-pass diode-pumping, we demonstrate higher pulse energy of 2.6 mJ. With wavelength tuning, this laser system demonstrated broad fundamental tuning range from 719 to 787 nm with diffraction-limited beam quality (M2 = 1.05). By external cavity second harmonic generation in a Type-I LBO crystal, pulse energy of 0.66 mJ is generated at 375 nm and with UV tuning range from 361 to 391 nm. To our knowledge, this is the first demonstration of AO Q-switched alexandrite laser with broad wavelength tuning in the near-IR and UV wavelength ranges and shows its excellent potential as a pulsed source for future applications.

High repetition rate step acousto-optic Q-switched laser with three nanosecond equal-interval and amplitude pulses

A compact, high repetition rate pulse group laser with three nanosecond equal-interval and equal-amplitude sub-pulses has been demonstrated in this paper. Under three-step nanosecond continuous acousto-optic control, a laser pulse group containing three nanosecond interval sub-pulses can be realized. The three sub-pulses have a pulse width of 15 ns, 23 ns, and 25 ns and minimum pulse intervals of 119 ns at a repetition rate of 30 kHz. The corresponding optical-optical conversion efficiency is 29.2 %.

High Average Power Green Laser Based on LED-Side-Pumped Q-Switched Nd:YAG Laser

In this paper, we demonstrated a watt-level acousto-optic (A-O) Q-switched intracavity frequency-doubled green laser with high average power and beam quality operation based on an efficient LED-pumped Nd:YAG laser module. For the quasi-continuous wave (QCW) running operation, the average output power of fundamental laser at 1064 nm was as high as 10.3 W at a repetition rate of 100 Hz, corresponding to the highest optical conversion efficiency of 25.4% and a slope efficiency of 31.3%, and the maximum energy of single pulse was up to 100mJ. By optimizing the incidence angle of the KTP crystal to meet the non-critical phase matching condition, greater than 3.8 W of 532 nm average power at a repetition rate of 10 kHz was generated with duration of 192 ns and a beam quality factor of M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> = 1.6 and M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> = 1.7, corresponding to a frequency doubling conversion efficiency of 45.5%. To the best of our ability, this is the highest average power and high beam quality of an LED-pumped A-O Q-switched intracavity frequency-doubled green laser with watt-level output reported so far.

Acousto-Optic Q-Switched Radio Frequency Waveguide CO2 Laser with High Repetition Rate and Short Pulse Width

Acousto-Optic Q-Switched Radio Frequency Waveguide CO2 Laser with High Repetition Rate and Short Pulse Width

Active and passive Q-switching operation of 1 μm Yb:YSP laser with an optical chopper/AOM and MoWS2 nanosheets

In this paper, the laser diode (LD)-pumped all-solid-state Yb:YSr3 (PO4)3 (Yb:YSP) lasers with active and passive Q-switching operation were demonstrated for the first time. At the pump power of 5.5 W, the average output power was 369 mW and the single pulse energy was 184.5 μJ at 2 kHz in the active Q-switching operation with an optical chopper. For the acousto-optic modulator Q-switched laser, a 118 ns pulse duration and 2881 W pulse peak power at 0.5 kHz were obtained. Furthermore, MoWS2 nanosheets were implemented to the passively Q-switched Yb:YSP laser, generating stable pulses with duration of 1.45 μs at the repetition frequency of 55 kHz and verifying the optical response potential of MoWS2. The good laser beam quality of = 1.14 and = 1.12 were achieved as well.

Quasi-linear polarized high-efficient diode-end-pumped actively Q-switched Nd:YAG/Nd:YVO4 laser

We propose and experimentally demonstrate a high-efficient and high-polarization-ratio acousto-optic (AO) Q-switched dual-crystal hybrid gain laser. Combing the advantages of Nd:YAG and Nd:YVO4 crystals, it exhibits excellent power performance across a broad pulse repetition frequencies (PRFs) range while maintaining satisfactory polarization characteristics without the aid of additional polarized optical components. Under 42.00-W incident pump power, the maximum average output power rises from 12.10 W to 19.64 W as the PRFs variates from 10 kHz to 200 kHz. The corresponding optical-to-optical efficiency increases from 28.81% to 46.76%. The pulse durations at maximum average output powers are 28.2 ns, 17.2 ns and 24.2 ns, respectively, when the laser operates at the PRFs of 10 kHz, 110 kHz and 200 kHz. The laser polarization ratios at maximum average output power are accordingly ∼7.6, ∼10, and ∼11.

Adjustable double-pulse laser output based on diffraction loss modulation of acousto-optic Q-switching

We propose a gain control method for acousto-optic Q-switched lasers. The laser in single-pulse mode can be converted into a double-pulse mode with adjustable subpulse intervals and energy ratios. It reduces the peak energy density while keeping the total energy unchanged in a cycle and thus effectively avoids damage to the optical fiber. The gain of the beam can be controlled by modulating the diffraction loss in the resonant cavity. A theoretical model of acousto-optic Q-switched double-pulse laser is established. Double-pulsing with adjustable subpulse intervals and energy ratios can be designed. A double-pulse laser is built experimentally, and the actual output waveform is basically consistent with the calculated results of the theoretical model. A double-pulse laser with adjustable energy ratios, adjustable subpulse intervals of 500 ns–20 µs, and 127 W at 5 kHz can be obtained. In addition, laser paint removal experiments are conducted, proving that the double-pulse laser has the same cleaning ability as the single-pulse laser at the same average output power. At the same time, the damage to the optical fiber can be largely avoided.

LD end-pumped Tm: YAG acousto-optic Q-switched double-pulse laser

Theory and experiment of Tm: YAG 2 μm double-pulse laser output based on the two-step signal of acousto-optic Q-switch is presented for the first time. As pump power of 10 W, a Q-switched Tm: YAG double-pulse laser is achieved with output energy of 3.6 mJ at 2014.16 nm and repetition rate of 100 Hz. The pulse width of the first pulse is 416 ns, and that of the second is 407 ns. The interval between the two pulses is 1 ms. The beam quality is M2x = 1.39 and M2y = 1.34.

Second-harmonic generation of Nd:YAlO3/YVO4 Raman laser optimization for orange emission

The orange emission at 597 nm produced by the second-harmonic generation of an acousto-optic Q-switched Raman laser was reported. A diode-pumped Nd:YAlO3 laser emitting at 1080 nm was employed to intra-cavity drive the pure YVO4 Raman crystal to obtain the first-Stokes wavelength at 1195 nm. The second-harmonic optimization of the first-Stokes laser is compared between the coupled cavity and the shared cavity. The results show that the shared cavity has more advantages than the coupled cavity for its better mode matching between fundamental cavity and Raman cavity at higher power. At an absorbed pump power of 5.96 W and the pulse repetition frequency of 15 kHz, average output power of 587 mW and conversion efficiency of 9.8% were obtained for the orange emission at 597 nm in the Nd:YAlO3/YVO4/LBO laser system. The 597 nm laser has special application in the fields as polymer materials analysis and biomedical optics.

An active and passive dual-loss Q-switched intracavity OPO based on few-layer WS2 saturable absorber

A 2.5 nm-thickness tungsten disulfide (WS2) saturable absorber (SA) was successfully fabricated by the electron beam evaporation (EBE) combined with post vulcanization. By applying the prepared WS2 SA to an acousto-optic (AO) Q-switched fundamental laser, a dual-loss-modulated Q-switched intracavity optical parametric oscillator (IOPO) has been experimentally realized. Because of the participation of WS2 SA, the problem of output decline was alleviated when the pump power was between 8.6 W and 10.8 W. The pulse width could be maximally compressed by 73% in WS2 SA based active-passive Q-switched IOPO with 10 kHz pulse-repetition rate, and the shortest pulse width in experiment was 1.098 ns. Benefiting from the pulse compression, the maximum pulse peak power in dual-loss-modulated Q-switched IOPO was 427% higher than that in AO active Q-switched IOPO. The application of WS2 SA also contributed to the stability of signal pulse train whose root mean square error (RMS) was efficiently lowered from 0.01776 to 0.00954. The nonlinear conversion efficiency was improved by approximate 38.2% in the dual-loss-modulated Q-switched IOPO.

Experimental and dynamical study of a dual Q-switched intracavity OPO based on few-layer MoSe2 SA.

A 2.5nm-thickness molybdenum diselenide (MoSe2) saturable absorber (SA) is prepared by electron beam evaporation (EBE) method. Applying the prepared MoSe2 SA to an acousto-optic (AO) Q-switched fundamental laser, a dual-loss-modulated intra-cavity optical parametric oscillator (IOPO) has been experimentally realized. The signal-pulse train from this IOPO has 0.0053 standard deviation (SD) of pulse amplitude. When the MoSe2 SA is applied to IOPO, the signal pulse is compressed by maximum 68%, the peak power increases by 274%, and the nonlinear conversion increases by 12.6%. To solve the established rate equation of IOPO, the ground-state and excited-state absorption cross section of MoSe2 are rationally estimated to be 1.04×10-18cm-2 and 6.25×10-19cm-2 from the measured transmittance curve, and the excited-state lifetime is 275.6µs. The numerical solution of the equations fits the experimental data well.

Polarization switching realized in the continuous-wave and acousto-optic Q-switched pulse Er:Yb:LaMgB5O10 lasers at 1556 and 1568 nm.

By using the natural birefringence of crystalline quartz, the switching of a 1568 nm laser with polarization parallel to the Z optical indicatrix axis to a 1556 nm laser with polarization parallel to the Y optical indicatrix axis was observed in both continuous-wave and acousto-optic Q-switched pulse lasers based on an X-cut Er:Yb:LaMgB5O10 crystal, when the alignment of the output mirror in a 976 nm diode-end-pumped plano-concave resonator was precisely tilted. For the continuous-wave regime, a 1568 nm laser with a maximum output power of 500 mW and slope efficiency of 16%, as well as a 1556 nm laser with a maximum output power of 400 mW and slope efficiency of 13.5% were realized, respectively. For the Q-switched regime, a 1568 nm pulse laser with an energy of 144 μJ and width of 300 ns, as well as a 1556 nm pulse laser with an energy of 168 μJ and width of 270 ns, were obtained respectively by precisely tilting the alignment of the output mirror, when the absorbed pump power was 4.0 W and pulse repetition frequency was 0.5 kHz.

Highly efficient actively Q-switched Yb:LGGG laser generating 3.26 mJ of pulse energy

An efficient acousto-optic Q-switched laser operation of Yb:(LuxGd1-x)3Ga5O12 (x = 0.062) (Yb:LGGG) crystal is demonstrated, producing stable pulses with repetition rate ranging from 1 to 20 kHz. Under the absorbed pump power of 8.75 W, the maximum average output power of 3.26 W is obtained at the pulse repletion rate of 1 kHz, corresponding to the slope efficiency as high as 52%. The pulse width of 14.5 ns is achieved with the pulse energy and peak power of 3.26 mJ and 225 kW, respectively. It indicates great potential of Yb:LGGG crystal for generating pulsed lasers.

Doubly Q-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.

888 nm pumped dual Nd:YVO[formula omitted] crystals acousto-optic Q-switched laser

888 nm pumped acousto-optic (AO) Q-switched laser with high output power and high efficiency under dual Nd:YVO4 crystals configuration is firstly demonstrated and rate equations for dual-crystal lasers are further ameliorated and investigated. In continuous wave (CW) operation, we experimentally achieve a maximum output power exceeding 50 W. The global optical efficiency reaches 49.5% and the slope efficiency attains 55.5% via using a 1.5 at.% crystal with a 0.5 at.% crystal. In Q-switch operation, by utilizing double 0.5 at.% crystals, the global optical efficiency rises from 25.6% to 45.6% and the pulse duration varies from 26.2 to 42.4 ns when pulse repetition frequency (PRF) increases from 10 to 100 kHz. The measured beam quality factors M2 at 100 kHz are 1.012 and 1.041 with 52.8 W output power in the two orthogonal directions respectively.

Four-Dimensional Thermal Analysis of 888 nm Pumped Nd:YVO4 Dual-Rod Acousto-Optic Q-Switched Laser

A theoretical analysis upon the four-dimensional (4D) spatio-temporal temperature dependent dynamics of 888 nm pumped Nd:YVO 4 dual-rod laser is established, which is valid in both continuous-wave (CW) and acousto-optic (AO) Q-switched pulse lasers conditions. Our model can accurately solve the 4D thermal generation and temperature evolution not only in the steady Q-switched state, but also in the first few unstable giant or dwarf pulses region. Factors including ground state depletion (GSD), energy transfer upconversion (ETU), fluorescence branching ratios, temperature-dependent cross sections and nonradiative relaxations processes are comprehensively considered for precisely estimating thermal effects, valid in both the steady pulse region and the unstable region at the beginning. Moreover, temporal and spatial temperature profiles and their coupling effect on output properties at different repetition-rates are discussed. Experiments of high-power high-repetition-rate 888 nm end-pumped Nd:YVO 4 dual-rod CW and AO Q-switched lasers are also firstly presented and the experimental results enjoy good consistency with our theory.

Cascaded Self-Raman Laser Emitting Around 1.2–1.3 &lt;italic&gt;μ&lt;/italic&gt;m Based on a c-cut Nd:YVO4Crystal

An acousto-optic Q-switched self-Raman laser emitting around 1.2–1.3 μ m based on cascaded conversion with the Raman shifts of 259 and 890 cm−1 was demonstrated in a c-cut Nd:YVO4 crystal. The laser starts with single Stokes emission at 1215 nm. As the incident pump power is increased, Stokes emissions at 1255 and 1316 nm also appear in sequence. When the incident pump power reaches 17.1 W and the pulse repetition frequency is set at 10 kHz, multi-Stokes output is obtained, and the average output power of the laser is 1.02 W, corresponding to a slope efficiency of 9.1%. The multi-Stokes laser output has a pulsewidth of 5.2 ns. Therefore, self-Raman laser lines were enriched with the participation of small Stokes shift of 259 cm−1 in the c-cut Nd:YVO4 crystal.

Dual-wavelength eye-safe Nd:GYSGG/YVO4 intracavity Raman laser under in-band pumping

An acousto-optic (AO) Q-switched dual-wavelength laser operating at 1.5µm eye-safe region is demonstrated via stimulated Raman scatting of a-cut YVO4-Nd:YVO4 crystal within an end-pumped dual-wavelength Nd:GYSGG laser cavity. The in-band pumping absorption peak and coefficient of the dual-wavelength laser crystal Nd:GYSGG are measured in order to carry out efficient pumping, thus overcoming the drawbacks of short thermal focal length of the crystal and scale up the eye-safe output. Under 23.2W absorbed pump power, 2.11W of simultaneous dual-wavelength outputs at 1497 and 1516nm are obtained with a pulse repetition rate of 23kHz and a corresponding conversion efficiency of 9.1%.

Efficient diode-pumped acousto-optic Q-switched Er:Yb:GdAl(3)(BO(3))(4) pulse laser at 1522 nm.

End-pumped by a continuous-wave 976 nm diode laser, efficient 1522 nm laser operation was demonstrated in an Er:Yb:GdAl(3)(BO(3))(4) crystal when a sapphire crystal was used as a heat diffuser. A continuous-wave 1522 nm laser with a maximum output power of 750 mW and slope efficiency of 36% was realized at an absorbed pump power of 4.1 W. The pulse performances of an acousto-optic Q-switched laser with various repetition frequencies were investigated in detail. In a repetition frequency range of 1-10 kHz, 1522 nm pulse lasers with a slope efficiency of about 10%, peak output power at the kilowatt level, and width of about 50 ns were first obtained in an Er:Yb:GdAl(3)(BO(3))(4) crystal pumped by a continuous-wave diode laser. The results indicate that the crystal is a promising gain medium for an actively Q-switched 1.5 μm laser.