Q-switched Tm Research Articles

Experimental and Theoretical Study of an Actively Q-Switched Tm:YLF Laser with an Acousto-Optic Modulator.

We report the characteristics of a diode-end-pumped, high-repetition-rate, acoustic-optic (AO) Q-switched Tm:YLF laser operating from 5 kHz to 10 kHz. In the continuous-wave (CW) regime, a maximum average output power of 8.5 W was obtained with a slope efficiency of 30.7%. Under the AO Q-switching regime, a maximum output power of 7.32 W was obtained at a repetition frequency of 5 kHz with a pulse width of 68 ns and a pulse energy of 1.4 mJ, corresponding to a peak power of 21.5 kW. A time-dependent rate equation model is introduced to theoretically analyze the results obtained in the experiment, in which the cross-relaxation phenomenon, upconversion losses and ground-state depletion are taken into account. Additionally, the evolution processes of population inversion density and intracavity photon number density with time are also presented. The theoretical results well predict the dependence of laser output characteristics of Tm:YLF crystal on the incident pump powers.

An Electro-Optic, Actively Q-Switched Tm:YAP/KGW External-Cavity Raman Laser at 2273 nm and 2344 nm

This paper presents a KGW Raman laser with an external-cavity configuration in the 2 μm region. The Raman laser is pumped by unique, electro-optic, actively Q-switched Tm:Yap laser, emitting at 1935 nm. The electro-optic modulation is based on a KLTN crystal, enabling the use of a short crystal length, with a relatively low driving voltage. Due to the KGW bi-axial properties, the Raman laser is able to lase separately at two different output wavelengths, 2273 and 2344 nm. The output energies and pulse durations for these two lines are 0.42 mJ/pulse at 18.2 ns, and 0.416 mJ/pulse at 14.7 ns, respectively. This is the first implementation of a KGW crystal pumped by an electro-optic active Q-switched Tm:Yap laser in the SWIR spectral range.

Passively Q-switched Tm:YAP laser with a zeolitic imidalate framework-67 saturable absorber operating at 3H4→3H5 transition

In the present work, we report the first Q-switching operation at ∼ 2.3 µm based on a Tm3+:YAlO3 (Tm:YAP) crystalline gain medium and a zeolitic imidazolate framework-67 (ZIF-67) saturable absorber. The ZIF-67 nanomaterials were designed and fabricated to possess a small size in the range from 200 to 500 nm in order to the reduce the possible scattering when working as the nonlinear optical modulator. Based on the conventional Z-scan technique with a home-made excitation source at 2275 nm, the modulation depth of ZIF-67 saturable absorber was determined as large as 6.9%, indicating the great potential in the short Q-switching pulse generation. With an output coupler (OC) of T = 0.5%, a maximum output power of 455 mW was achieved with a slope efficiency of 27%. For the Q-switching operation at 2.3 µm with ZIF-67 saturable absorber, the highest output power of 220 mW and a minimum pulse duration of 220 ns were obtained with a pulse repetition rate of 95 kHz at 2271.7 nm.

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.

Layered Metallic Vanadium Disulfide for Doubly Q-Switched Tm:YAP Laser with EOM: Experimental and Theoretical Investigations.

In the current study, layered metallic vanadium disulfide (VS2) is fabricated by a liquid-phase exfoliation method, and its microstructures as well as optical characteristics are investigated. Based on first-principles calculations, the band structure and density of the states of both bulk T-VS2 and monolayer H-VS2 are illustrated, showing the metallic behavior with a zero band gap. By using VS2 as the saturable absorber in a doubly Q-switched Tm:YAP laser with an EOM, the Q-switching laser pulses at 2 μm with 22 ns and 200 Hz are generated, corresponding to the single pulse energy of 755 μJ and the peak power of 34.3 kW. The coupled rate equations of the doubly Q-switched laser are given, and the numerical simulations agree with the experimental results. The results indicate that VS2 is a promising nanomaterial due to its nonlinear optical property. The doubly Q-switched laser demonstrates a high level of performance in reducing pulse width and enhancing pulse peak power.

Mid-infrared tunable pulsed laser based on Cr2+-doped II–VI chalcogenide

Cr2+-doped II–VI chalcogenides are attractive laser media for direct access to the mid-infrared (IR) region from 2 to 3 μm. We have developed a mid-IR tunable laser using Cr:ZnSe and Cr:CdSe as laser media. We have used a Q-switched Tm:YAG laser as a pump source. For the Cr:ZnSe laser, the tuning range of 2.18–2.83 μm and the maximum pulse energy of 4.98 mJ at 2.38 μm were obtained with a pump energy of 22 mJ. For the Cr:CdSe laser, the tuning range of 2.22–3.04 μm and the maximum pulse energy of 2.42 mJ at 2.54 μm were achieved with a pump energy of 22 mJ. In addition, we have demonstrated a method of extending the mid-IR lasing region by a combined active medium technique with Cr:ZnSe and Cr:CdSe. We observed the broad tuning range from 2.15 to 3.04 μm and the maximum pulse energy of 5.96 mJ at 2.44 μm with a pump energy of 22 mJ.

Passively Q-switched Tm:YAP laser with a lead zirconate titanate saturable absorber.

In the paper, we prepare a lead zirconate titanate saturable absorber, which is used to demonstrate a passively Q-switched (PQS) Tm:YAP laser. In the PQS mode, an average output power of 0.81 W and pulse width of 1.69 µs at 175 kHz are obtained at 1991.9 nm with a pump power of 12.76 W, corresponding to an optical-optical conversion efficiency of 6.35%. In addition, the beam quality factors M2 of the PQS Tm:YAP laser in the x and y directions are 1.17 and 1.15, respectively.

Nickel-cobalt layered double hydroxide nanosheets saturable absorber for passively Q-switched Tm:YAG ceramic 2 μm solid-state laser

A novel nickel–cobalt (NiCo)-layered double hydroxide (LDH) saturable absorber (SA) was fabricated by the liquid-phase exfoliation method and applied as the laser modulator for the first time. We successfully investigated the laser modulation performance of the NiCo-LDH SA at 2 µm with a passively Q-switched (PQS) Tm:YAG ceramic laser. The narrowest pulse width of 322.6 ns was obtained, corresponding to a pulse repetition frequency of 119.3 kHz and a single pulse energy of 2.10 µJ. As far as we know, this is the shortest pulse width of PQS Tm:YAG crystal and ceramic lasers with two-dimensional materials saturable absorber. The results show that NiCo-LDH SA is a promising candidate for the application of laser modulators at 2 µm.

Theoretical and experimental investigations on doubly Q-switched Tm:YAP laser with EOM and Sb2Te3 nanosheets.

In this paper, two-dimensional material Sb2Te3 nanosheets are fabricated and the optical nonlinear response is investigated. A laser diode (LD) end-pumped doubly Q-switched Tm:YAP laser with electro-optic modulator (EOM) and Sb2Te3 nanosheets based saturable absorber (SA) is presented. The shortest pulse duration of 38 ns is achieved at the pulse repetition frequency of 100 Hz, corresponding to the highest peak power of 111.8 kW. The double Q-switching technique shows the advantages of pulse duration compression and peak power improvement. The coupled rate equations for the doubly Q-switched laser are developed and the corresponding numerical simulation agrees with the experimental results. We believe that the Sb2Te3 is a potential nanomaterial for the application in optoelectronic field.

Theoretical and experimental investigations on Nb2CT x MXene Q-switched Tm:YAP laser at 2 μm for the nonlinear optical response

In this paper, the Nb2CT x MXene nanosheets were fabricated and the corresponding microstructures were investigated. The nonlinear optical response was illustrated by open aperture Z-scan and I-scan methods. The ground and the excited state absorption cross-sections of 2D Nb2CT x MXene were also investigated. As the saturable absorber (SA), the Nb2CT x MXene was applied in the passively Q-switched Tm:YAP laser. 1.96 μs Q-switched pulses with 3.97 W peak power were achieved at the repetition frequency of 80 kHz. Further theoretical model was built by using the coupled rate equations in simulating the dynamic process of the passively Q-switched Tm:YAP laser. The numerical simulation results are fundamentally in agreement with the experimental results, which proves the Nb2CT x MXene can be a good potential nanomaterial for further optoelectronic applications.

High-pulse-energy high-brightness Q-switched Tm3+:Ho3+-codoped triple-clad polarization- maintaining fiber laser

A Q-switched polarization-maintaining (PM) Thulium (Tm3+):Holmium (Ho3+)-codoped triple-clad fiber (THTF) laser is under investigation with special focus on important optical parameters enabling efficient frequency conversion into mid-infrared (mid-IR). An active fiber of 5 m length is used in a single-oscillator free-space cavity arrangement and operated in continuous-wave and pulsed operation. In Q-switched regime at a repetition rate of 63 kHz, high pulse energies up to 760 μJ were obtained while reaching pulse widths as low as 45.6 ns, resulting in pulse peak powers of 15.7 kW with an average output power of 48 W. In addition, an M x,y 2 < 1.2 and a FWHM of 290 pm for the emission spectrum was measured.

Wavelength-tunable diamond Raman laser at ∼2.5 μm

We report on wavelength tunable operation of a diamond Raman laser at ∼2.5 μm pumped by a narrow linewidth Q-switched Tm:YAP laser at 1.88 μm. The Raman laser operates at 50 Hz of repetition rate and produced stable pulses of 1.12 mJ energy and 9.2 ns duration, corresponding to a peak power of ∼121.7 kW. Over 56 mW of average output power has been generated for ∼197 mW of incident pump power, corresponding to a slope efficiency of 45.3%. Output wavelength was tunable from 2511.1 nm to 2522.1 nm via a birefringence filter and two etalons incorporated in the Tm:YAP laser resonator.

Watt-level graphdiyne passively Q-switched Tm:YAP laser at ~2 µm

A watt-level Tm:YAP pulsed laser at 1936.6 nm was realized with graphdiyne (GDY) acted as a passive modulator. Through efficient diode pumping, 1.37 W pulsed laser output was obtained when the absorbed pump power was 4.44 W, corresponding highest repetition rate, largest single pulse energy and maximum peak power of 98.59 kHz, 13.85 μJ and 6.40 W, respectively. These results illustrate the potentiality of GDY as a modulator to generate pulsed laser in 2 µm band range.

Efficient continuous wave and acousto-optical Q-switched Tm:Lu2O3 laser pumped by the laser diode at 1.7 μm

A resonantly-pumped continuous wave and acousto-optical (AO) Q-switched Tm:Lu2O3 laser was demonstrated in this paper. In the continuous-wave regime, with absorbed pump power of 15.4 W, the Tm:Lu2O3 laser delivered a maximum output power of 6.1 W and a slope efficiency of 66.4% with respect to the absorbed pump power. With a pulse repetition frequency of 10 kHz, the AO Q-switched Tm:Lu2O3 laser produced maximum average output power of 3.87 W. At the pulse repetition frequency of 5 kHz, the AO Q-switched Tm:Lu2O3 laser reached the maximum pulse energy of 0.74 mJ and the minimum pulse width of 46 ns, resulting in a peak power of 16.1 kW.

Investigation of the pulse energy limits of actively Q-switched polarization-maintaining Tm3+-doped fiber lasers

A diode-pumped actively Q-switched polarization-maintaining Tm3+-doped fiber laser is reported generating pulse energies of 630 μJ, minimum pulse widths of 42 ns, and a maximum peak power of 13.9 kW with linear polarized output and diffraction-limited beam quality at a wavelength of 2044 nm. The unpolarized fiber laser even reaches pulse energies of 800 μJ, pulse widths of 41 ns, and peak powers of 18.6 kW.

High pulse energy ZnGeP2 OPO directly pumped by a Q-switched Tm3+-doped single-oscillator fiber laser.

A mid-infrared ${{\rm ZnGeP}_2}$ optical parametric oscillator pumped by a ${{\rm Tm}^{3 +}}$-doped fiber laser is reported, providing pulse energies of $230 \;\unicode{x00B5}{\rm J}$, pulse widths of 40 ns, and peak powers of ${\sim}6\;{\rm kW} $ with excellent efficiency and beam quality. The pump source is an actively $Q$-switched single oscillator optimized to generate high pulse energies.

Electro-optic active Q-switched Tm:YLF laser based on polarization modulation.

An electro-optic active Q-switched Tm:YLF laser (1880 nm) employing a novel, to the best of our knowledge, switching scheme is presented. The switching is done by a potassium lithium tantalate niobate (KLTN) crystal operated slightly above the ferroelectric phase transition, cut in a trapezoidal shape for reducing acousto-optic oscillations. The novel switching scheme exploits the emission cross section difference between the π and σ polarizations in the Tm:YLF and overcomes the residual oscillation effects even at high repetition rates. The laser exhibited stable operation yielding pulses of 0.81 mJ and pulse duration of 30 ns at 5 kHz, and pulses of 1.25 mJ and pulse duration of 19 ns at 500 Hz.

2.3–2.5 μm laser operation of LD-pumped Tm:YAP on the 3H4→3H5 transition

Abstract 2.3–2.5 μm laser operation of LD-pumped Tm:YAP on the 3H4→3H5 transition is reported. The a-cut, b-cut and c-cut Tm:YAP crystals with 2 at.% doping concentration were used to characterize the laser performance. All the laser outputs were found to be linearly polarized that is induced by the gain anisotropy of Tm:YAP. First laser oscillation of Tm-doped laser on the 3H4→3H5 transition beyond 2.4 μm in Tm:YAP was realized by using a specially designed output coupler with a high transmittance at 2200–2350 nm and partial reflection at 2400–2500 nm. 736 mW at 2446 nm and 189 mW at 2482 nm are obtained from the a-cut and b-cut crystal, respectively. Furthermore, continuous-wave and passively Q-switched dual-wavelength Tm:YAP laser at 2274 and 2383 nm were realized with the a-cut crystal. 538 mW at 2353 nm with a slope efficiency of 8.3% is achieved from the c-cut crystal. Our work demonstrates the multi-wavelength emitting ability of LD-pumped Tm:YAP laser on the 3H4→3H5 transition, which can further expand the application of Tm-doped lasers.

Comparative study of pulsed laser diode end-pumped thulium-doped 2-μm Q-switched lasers* *Project supported by the National Natural Science Foundation of China (Grant Nos. 11974060 and U19A2077).

We report pulsed laser diode (LD) end-pumped acoustic Q-switched Tm:YAG laser, Tm:LuAG laser, and Tm:LuYAG laser and the physical properties and spectra of Tm:YAG, Tm:LuAG, and Tm:LuYAG are analyzed. The Tm:LuYAG laser is pumped by 785-nm and 788-nm pulses separately, and is compared with Tm:YAG laser. Different output energy values and output wavelengths of Tm:LuAYG lasers pumped by LDs with different wavelengths are obtained and compared with each other. When the repetition frequency is 100 Hz, the pulsed Tm:YAG laser has single pulse energy of 15.9 mJ, pulse width of 126.7 ns, and the center wavelength of 2013.36 nm, and the pulsed Tm:LuAG laser possesses single pulse energy of 11.8 mJ, pulse width of 252.4 ns, and the center wavelength of 2023.65 nm, and the pulsed Tm:LuYAG laser output energy values are 12.32 mJ and 12.25 mJ with the slope efficiencies of 12.5% and 11.85%, the center wavelengths of 2017.89 nm and 2027.11 nm, respectively, while the pump sources are 785-nm and 788-nm pulsed LDs, respectively.

High single pulse energy passively Q-switched mode-locked Tm, Ho: LLF laser

High single pulse energy passively Q-switched mode-locked Tm, Ho: LLF laser