Efficient thin-disk Tm-laser operation based on Tm:KLu(WO4)2/KLu(WO4)2 epitaxies

A diode-pumped thin-disk laser based on Tm:KLu(WO4)2/KLu(WO4)2 epitaxies is realized. The emission is in the 1850-1945 nm spectral range for Tm-doping between 5 and 15 at. %. The maximum slope efficiency of 47% with respect to the absorbed power obtained with 5 at. % Tm:KLu(WO4)2/KLu(WO4)2 corresponds to a maximum output power of ~6 W in cw operation.     

Thin-disk Yb:KLu(WO(4))(2) laser with single-pass pumping

Single-pass pumping of a thin disk consisting of an only 50 microm thick epitaxial layer of 32 at.% Yb-doped KLu(WO(4))(2) grown on a 0.35 mm thick undoped KLu(WO(4))(2) substrate is demonstrated. The thin-disk laser delivered 9 W of continuous wave output power near 1030 nm with a slope efficiency of 77%.     

Passively mode-locked Yb:KLu(WO4)2 thin-disk oscillator operated in the positive and negative dispersion regime

We demonstrate a passively mode-locked femtosecond Yb:KLu(WO(4))(2) thin-disk laser oscillator. Chirped-pulse operation in the positive dispersion regime as well as solitary operation have been realized, and the laser performance of both configurations are compared. In the solitary mode-locking regime the output power exceeds 25 W in a diffraction-limited beam, and pulse durations as short as 440 fs at a 34.7 MHz repetition rate have been generated. For the first time we present a chirped-pulse operation of a thin-disk oscillator that yields a maximum average output power of 9.5 W with a Fourier limit of 450 fs.     

Efficient high-power laser operation of Yb:KLu(WO4)2 crystals cut along the principal optical axes

High-power continuous-wave laser operation was demonstrated with Yb:KLu(WO(4))(2) crystals cut along the N(p), N(m), and N(g) principal optical axes, achieving a nearly equal slope efficiency of 79%-80% in the absence of thermal effects. The N(g)-cut crystal proved to be the most advantageous for power scaling as well as efficient pumping. A maximum output power of 11.0 W was produced from a 2 mm thick uncoated N(g)-cut crystal in a approximately 7 mm long plano-concave resonator end pumped by a fiber-coupled diode; the corresponding optical-to-optical efficiency was 68%.     

Efficient continuous-wave and Q-switched operation of a diode-pumped Yb:KLu(WO4)2 laser with self-Raman conversion

Efficient cw and passively Q-switched operation with self-stimulated Raman scattering conversion was demonstrated in a compact diode-pumped Yb:KLu(WO4)2 laser. A cw output power of 3.28 W was obtained with an optical efficiency of 48.2% and a slope efficiency of 78.2% with respect to the incident pump power. Stable Q-switched operation was achieved with a Cr4+:YAG saturable absorber, generating 32.4 microJ fundamental pulses with a duration of 1.41 ns at 1030.6 nm and 14.4 microJ Raman pulses with a duration of 0.71 ns at 1137.6 nm. At an incident pump power of 7.0 W, the average output power reached 0.9 and 0.4 W for fundamental and Raman radiation, with slope efficiencies of 32.1% and 14.1%, respectively.     

Pulsed laser operation of Y b-dope d KY(WO(4))(2) and KGd(WO(4))(2)

Spectroscopic properties and laser performance of Y b-doped tungstates at pulsed Ti:sapphire laser pumping are reported. Room-temperature lasing near 1025nm is demonstrated in Yb:KY(WO(4))(2) and Yb:KGd(WO(4))(2), with a slope efficiency as great as 86.9%.     

Enhanced efficiency of Er:Yb:Ce:NaGd(WO4)2 laser at 1.5-1.6 microm by the introduction of high-doping Ce3+ ions

By the introduction of high-doping Ce3+ ions, the upconversion fluorescence of Er3+ ions was reduced, and the energy-transfer efficiency from Yb3+ to Er3+ ions was enhanced significantly in Er:Yb:Ce:NaGd(WO4)2 crystals. End pumped by a diode laser at 970 nm in a hemispherical cavity, a 2.0 W quasi-cw laser at 1.5-1.6 microm with slope efficiency of 19% and absorbed pump threshold of 2.0 W was achieved in a 1.7-mm-thick c-cut Er:Yb:Ce:NaGd(WO4)2 crystal. The results show that the Er.:Yb:Ce:NaGd(WO4)2 crystal with high-doping Ce3+ ions is a potential gain medium for a low-threshold 1.5-1.6 microm laser.     

Spectroscopic characterization and laser performance of resonantly diode-pumped Er(3+)-doped disordered NaY(WO4)2

We report what is believed to be the first resonantly pumped laser operation based on Er(3+)-doped disordered double tungstate single crystal. Efficient laser operation of an Er(3+):NaY(WO(4))(2) laser at ～1609.6 nm was demonstrated with the naturally wideband, ～20 nm, InGaAsP/InP laser diode pumping at ～1501 nm. Laser wavelength tunability of ～34 nm was also demonstrated based on disorder-broadened emission features of Er(3+):NaY(WO(4))(2) single crystal.     

Efficient passively Q-switched laser operation of Yb in the disordered NaGd(WO4)2 crystal host

Efficient passively Q-switched laser operation of the disordered Yb:NaGd(WO(4))(2) crystal is demonstrated for the first time to our knowledge with a Cr(4+):YAG saturable absorber by diode end pumping. 2.05 W of average output power at a pulse repetition frequency of 13.3 kHz was obtained at an absorbed pump power of 7.7 W, with a slope efficiency of 40%. The energy and duration of the generated laser pulse were 154 microJ and 33 ns, respectively, corresponding to a peak power of 4.67 kW. In continuous-wave operation, the Yb:NaGd(WO(4))(2) laser yielded an output power of 5.5 W with an optical-optical efficiency of 51%.     

Influence of pump wavelength on the laser performance of Yb:KLu(WO4)2 crystal

By employing a tunable Ti:sapphire laser, we conducted an investigation into the effects of pump wavelength deviation on the laser performance of Yb:KLu(WO₄)₂ crystal. Pumping efficiencies exceeding 70% could be reached under lasing conditions with a 3-mm crystal of Yb concentration of 5.24 at.%, when the pumping wavelength was within the main absorption band centered at 981 nm extending from 974 to 990 nm. For different pumping wavelengths, the laser exhibited a single output–input relation with respect to absorbed pump power, giving an average slope efficiency amounting to 51%.     

240-fs pulses with 22-W average power from a mode-locked thin-disk Yb:KY(WO(4))(2) laser

We demonstrate what is to our knowledge the first passively mode-locked thin-disk Yb:KY(WO(4))(2) laser. The laser produces pulses of 240-fs duration with an average power of 22 W at a center wavelength of 1028 nm. At a pulse repetition rate of 25 MHz, the pulse energy is 0.9microJ , and the peak power is as high as 3.3 MW. The beam quality is very close to the diffraction limit, with M(2)=1.1 .     

Passive Q switching and self-frequency Raman conversion in a diode-pumped Yb:KGd(WO(4))(2) laser

We report on the laser performance of a diode-pumped Yb:KGd(WO(4))(2) laser that is passively Q switched with a Cr(4+):YAG saturable absorber. Raman conversion of fundamental laser emission in the laser crystal was demonstrated. Q-switched 3.4-mu;J pulses with a pulse width of 85 ns were obtained at the 1033-nm fundamental wavelength and 0.4-mu;J pulses with a pulse width of 20 ns were produced in a first Stokes at 1139 nm.     

Diode-pumped femtosecond Yb:KGd(WO(4))(2) laser with 1.1-W average power

We demonstrate what is to our knowledge the first mode-locked Yb:KGd(WO(4))(2) laser. Using a semiconductor saturable-absorber mirror for passive mode locking, we obtain pulses of 176-fs duration with an average power of 1.1 W and a peak power of 64 kW at a center wavelength of 1037 nm. We achieve pulses as short as 112 fs at a lower output power. The laser is based on a standard delta cavity and pumped by two high-brightness laser diodes, making the whole system very simple and compact. Tuning the laser by means of a knife-edge results in mode-locked pulses within a wavelength range from 1032 to 1054 nm. In cw operation, we achieve output powers as high as 1.3 W.     

Diode-pumped Kerr-lens mode-locked Yb:KY(WO(4))(2) laser

A self-starting Kerr-lens mode-locked Yb:KY(WO(4))(2) laser directly end pumped by two 1.6-W diodes is demonstrated for what is to our knowledge the first time. Pulses as short as 71 fs with 120-mW average output power, at a center wavelength of 1057 nm, were obtained at a repetition rate of 110 MHz. A 10-nm tuning range was achieved with longer pulses and higher average output power.     

单斜结构的Yb:KLu(WO4)2晶体光谱和激光性质的各向异性

研究了Yb:KLu(WO₄)₂晶体对非偏振抽运光的吸收以及连续波激光振荡性质. 晶体结构的低对称性导致晶体光谱呈强烈各向异性,最强的吸收和发射都发生在平行于N_m主轴的偏振方向上. N_g切向晶体具有最高的非偏振抽运光吸收效率和最大的激光功率产生潜力,2 mm长的晶体产生的最高连续波输出功率为11 W,相对于吸收抽运功率,光—光转换效率为68%,而斜率效率则达80%. 关键词： 吸收谱 发射谱 激光振荡 各向异性     

Highly efficient 1 GHz repetition-frequency femtosecond Yb3+:KY(WO4)2 laser

We present a highly efficient, diode-pumped, femtosecond Yb3+:KY(WO4)2 (Yb:KYW) laser operating at a 1.024 GHz repetition rate. The output was centered at a wavelength of 1042 nm and had a bandwidth of 3.8 nm, leading to transform-limited pulses with durations of 278 fs determined by fringe-resolved autocorrelation measurements. The optical-to-optical conversion efficiency and slope efficiency were 61% and 69%, respectively, and the relative intensity noise was <0.1%.     

Crystal growth,optical spectroscopy,and continuous-wave laser operation of Ho:KLu(WO4)2 crystals

We present the crystal growth, optical spectroscopy, and room temperature continuous-wave (CW) laser operation of monoclinic Ho:KLu(WO₄)₂ crystals. Macro defect-free crystals of several dopant concentrations were grown by top-seeded solution growth slow-cooling method. The evolution of unit cell parameters with holmium doping level and temperature was studied using X-ray powder diffraction. The spectroscopic properties were characterized in terms of room- and low-temperature optical absorption and photoluminescence. From low-temperature optical absorption measurements, the energy of the Stark levels was determined. Calculation of the emission and gain cross sections is presented. CW laser action was realized for 3 and 5 at. % Ho-doped KLu(WO₄)₂ by in-band pumping using a Tm:KLu(WO₄)₂ pump laser. A maximum output power of 507 mW with a slope efficiency of ~38 % with respect to the incident power was achieved at 2,080 nm with the Ho:KLu(WO₄)₂ laser.     

High-peak-power pulses from a cavity-dumped Yb:KY(WO4)2 oscillator

We report generation of 1.35 microJ femtosecond laser pulses with a peak power of 3 MW at 1 MHz repetition rate from a diode-pumped Yb:KY(WO4)2 laser oscillator with cavity dumping. By extracavity compression with a large-mode-area fiber and a prism sequence, we generate ultrashort pulses with a duration of 21 fs and a peak power of 13 MW.     

Efficient femtosecond green-light source with a diode-pumped mode-locked Yb3+:KY(WO4)2 laser

Efficient generation of femtosecond pulses at 524 nm is demonstrated by the extracavity frequency doubling of the output of a diode-pumped femtosecond Yb3+:KY(WO4)2 laser using a periodically poled LiTaO3 crystal. An average second-harmonic power of 120 mW is produced at an internal conversion efficiency of 40%. The temporal characteristics of the frequency-doubled pulses as a function of focusing conditions in a thick nonlinear crystal are investigated experimentally, and pulses as short as 225 fs are generated at a pulse repetition frequency of 86 MHz.     

Growth and properties of KLu(WO4)2, and novel ytterbium and thulium lasers based on this monoclinic crystalline host

High‐quality crystals of monoclinic KLu(WO₄)₂, shortly KLuW, were grown with sizes sufficient for its characterization and substantial progress was achieved in the field of spectroscopy and laser operation with Yb³⁺‐ and Tm³⁺‐doping. We review the growth methodology for bulk KLuW and epitaxial layers, its structural, thermo‐mechanical, and optical properties, the Yb³⁺ and Tm³⁺ spectroscopy, and present laser results obtained in several operational regimes both with Ti:sapphire and direct diode laser pumping using InGaAs and AlGaAs diodes near 980 and 800 nm, respectively. The slope efficiencies with respect to the absorbed pump power achieved with continuous‐wave (CW) bulk and epitaxial Yb:KLuW lasers under Ti:sapphire laser pumping were ≈ 57 and ≈ 66%, respectively. Output powers as high as 3.28 W were obtained with diode pumping in a simple two‐mirror cavity where the slope efficiency with respect to the incident pump power reached ≈ 78%. Passively Q‐switched laser operation of bulk Yb:KLuW was realized with a Cr:YAG saturable absorber resulting in oscillation at ≈ 1031 nm with a repetition rate of 28 kHz and simultaneous Raman conversion to ≈ 1138 nm with maximum energies of 32.4 and 14.4 μJ, respectively. The corresponding pulse durations were 1.41 and 0.71 ns. Passive mode‐locking by a semiconductor saturable absorber mirror (SESAM) produced bandwidth‐limited pulses with duration of 81 fs (1046 nm, 95 MHz) and 114 fs (1030 nm, 101 MHz) for bulk and epitaxial Yb:KLuW lasers, respectively. Slope efficiency as high as 69% with respect to the absorbed power and an output power of 4 W at 1950 nm were achieved with a diode‐pumped Tm:KLuW laser. The slope efficiency reached with an epitaxial Tm:KLuW laser under Ti:sapphire laser pumping was 64 %. The tunability achieved with bulk and epitaxial Tm:KLuW lasers extended from 1800 to 1987 nm and from 1894 to 2039 nm, respectively.