LiYF4 Laser Research Articles

Passively Q-switched Pr:YLF laser with a Co2+:MgAl2O4 saturable absorber.

We report on a 2ω-OPSL-pumped passively Q-switched Pr3+:LiYF4 laser operating at the wavelengths of 523, 607, and 640nm. For this, we utilized a Co2+-doped MgAl2O4 (MALO) crystal as a saturable absorber in the visible range for the first time, to the best of our knowledge. In the green spectral region, the pulse duration was 210ns with a pulse energy of 3.6μJ and a repetition rate of 125kHz. The minimum pulse duration of 87ns at the highest pulse energy of 8.6μJ was obtained at a repetition rate of 110kHz at 607nm. The highest Q-switched average laser power of 1.4W was obtained at an absorbed continuous-wave pump power of 3.3W with a slope efficiency of 47% at 640nm. Absorption saturation measurements with Co:MALO were performed, and ground and excited state absorption cross sections in the visible spectral range were determined.

303 nm continuous wave ultraviolet laser generated by intracavity frequency-doubling of diode-pumped Pr3+:LiYF4 laser

We demonstrate an efficient and compact ultraviolet laser at 303 nm generated by intracavity frequency doubling of a continuous wave (CW) laser diode-pumped Pr3+:YLiF4 laser at 607 nm. A cesium lithium borate (CLBO) crystal, cut for critical type I phase matching at room temperature, is used for second-harmonic generation (SHG) of the fundamental laser. By using an InGaN laser diode array emitting at 444.3 nm with a maximum incident power of 10 W, as high as 68 mW of CW output power at 303 nm is achieved. The output power stability in 4 h is better than 2.85%. To the best of our knowledge, this is high efficient UV laser generated by frequency doubling of an InGaN laser diode array pumped Pr3+:YLiF4 laser.

Spectral properties and anti-Stokes luminescence of TeO2–BaF2:Ho3+, Ho3+/Yb3+ ceramics and glass excited by 1.9-μm radiation of a Tm:LiYF4 laser

We demonstrate the up-conversion of Tm:LiYF4 infrared (IR) laser radiation with 1908-nm wavelength into visible light with a spectral maximum at 650 nm by ceramics with a composition of (100 − x)TeO2−xBaF2 − 1 wt % HoF3−yYbF3, where x = 20, 30, or 40 mol % and y = 0 or 0.5 wt %. The samples of 60TeO2−40BaF2 − 1 wt % HoF3 − 0.5 wt % YbF3 exhibited anti-Stokes luminescence at a threshold radiation power density of 1.0−1.5 W cm−2.

Quasi-three-level orthogonally polarized cw dual-wavelength operation in Nd:LiYF4

A diode-end-pumped quasi-three-level orthogonally polarized continuous-wave (cw) dual-wavelength Nd:LiYF4 (Nd:YLF) laser that generates simultaneous laser at the wavelengths 903nm and 908nm was demonstrated. Two types of cavity configurations were studied to support the stable dual-wavelength operation of the laser. A polarization beam splitter (PBS) was placed in the first type of cavity to split the beams polarizing in two orthogonal directions. At an absorbed pump power of 21.4W, the cw output power obtained at 903nm in π-polarization and 908nm in σ-polarization is 0.43W and 3.31W, respectively. Furthermore, in order to balance the gain-to-loss, an uncoated glass plane was inserted in the second type of cavity. By adjusting the inclination of the glass plane relative to the optical axis of the resonator, we realized the stable simultaneous dual-wavelength operation. The cw output powers of 1.82W at 903nm and of 2.92W at 908nm were obtained.

Passive Q-switching of Pr:LiYF4 orange laser at 604 nm using topological insulators Bi2Se3 as saturable absorber

Q-switched laser operation of a laser diode pumped Pr:LiYF4 laser is reported at 604nm using a topological insulator (TI) Bi2Se3 nanosheet material as saturable absorbers (SAs), for the first time to our knowledge. Stable Q-switched laser operation is obtained with shortest pulse width of about 802ns, a maximum pulse repetition rate of 130kHz, pulse energy of about 0.2μJ and a maximum average output power of 26mW. This work further extends the working wavelength of Bi2Se3 as saturable absorbers to visible domain.

Passive Q-Switching of a Diode-Pumped Pr:LiYF4Visible Laser Using WS2as Saturable Absorber

Q-switched laser operation of a blue-diode-pumped Pr:LiYF4 laser is demonstrated at 640 nm for the first time by using a tungsten disulfide (WS2) nanosheet material as a saturable absorber. Stable laser pulses of 630 ns are obtained with a pulse repetition rate of 88 kHz, a pulse energy of about 0.24 $\mu\text{J}$ , and an average output power of 21.5 mW. This paper broadens the application of WS2-like 2-D nanosheet saturable absorbers from the near- and mid-infrared to the visible domain.

Laser wavelength tunability of a diode-pumped Nd:LiYF4 laser on the 4F3/2–4I13/2 transition

We report a free-running orthogonally polarized dual-wavelength laser at 1313 and 1321 nm with maximum total output power of about 1.73 W using a two-mirror linear cavity. By inserting an etalon into the linear cavity, single-wavelength lasers at 1317 or 1323 nm, two-wavelength lasers at 1317 and 1323 nm, as well as four-wavelength lasers at 1313, 1317, 1323 and 1370 nm can be achieved with maximum output powers of about 0.73, 0.63, 0.78 and 0.25 W, respectively. About 10-nm wavelength tunability from about 1313 to 1323 nm is also realized by inserting the etalon into a three-mirror V-type Nd:YLF laser cavity.

Ho3+-Doped ZrF4–BaF2–BiF3 Ceramic 2-µm laser beam visualizer

A ceramic 2-µm laser beam visualizer based on Ho3+-doped β-BaZrF6 is proposed. The ceramic has been prepared by crystallizing 60ZrF4–35BaF2–5BiF3 glass doped with 3 wt % HoF3. Exciting the Ho3+5I7 level by a Tm:LiYF4 (Tm:YLF) laser at λ = 1910 nm, we observed a strong red luminescence, due to the 5F5 → 5I8 transition, and a weaker, green luminescence, corresponding to the (5F4, 5S2) → 5I8 transition. The threshold power density of the Tm:YLF laser at which a red spot was observed on a ceramic sample was 1.1 W/cm2.

Diode-pumped continuous-wave dual-wavelength c-cut Pr³⁺:LiYF₄ laser at 696 and 719 nm.

A continuous-wave, InGaN-LD-pumped dual-wavelength laser is demonstrated with simultaneous emission at 696 (3P03F(→)3) and 719 nm (3P03F(→)4) using a c-cut Pr(3+):LiYF4, for the first time to our knowledge. Maximum output power of 102 mW at these two wavelengths is achieved with slope efficiency of about 15.6% with respect to the absorbed pump power. The beam propagation factors in x and y directions are measured to be 1.50 and 1.32, respectively.

A 60W Tm:YLF Laser with Triple Tm:YLF Rods

A narrow linewidth stable high-power continuous-wave 3.5% Tm3+ doped LiYF4 (Tm:YLF) laser is reported. By using dual F–P etalons and three Tm:YLF rods in a cavity, laser output of ∼60 W at 1907.7 nm is obtained with a slope efficiency of 34.8%. The M2 factor is found to be ∼2.0 under an output power of 30 W. In addition, the relaxation oscillation and efficiency of the Tm:YLF laser are also studied. The relaxation oscillation of the Tm:YLF laser is improved obviously by setting the ratio of pump beam to oscillating laser beam as ∼1.5:1 and the efficiency is increased in comparison with the ratio of ∼1.3:1.

Temperature effects on the main absorption and emission lines of the Pr^3+:LiYF_4 laser crystal

The widths and the shifts of the most important absorption and emission lines observed in the visible, deep-red, and near-infrared spectral domains in the well-known Pr3+-doped LiYF4 laser crystal were measured from 12 to 300 K. The investigated absorption lines are those usually used for laser pumping and are located around 444, 469, and 479 nm, and also around 595 nm. The investigated emission lines are those peaking around 480, 523, 546, 604, 607, 640, 698, 721, 907, and 915 nm. Most of the results are interpreted and successfully described by using the existing linear and quadratic electron–phonon coupling theories. The shape and the temperature evolution of the emission lines occurring around 910 nm are also clearly assigned to a series of spin-allowed and spin-forbidden anti-Stokes emission transitions originating from the thermalization of several emitting energy levels.

Emission properties and CW laser operation of Pr:YLF in the 910 nm spectral range.

The polarized emission spectra for the 3P0→1G4 emission transition of the Pr3+ ion around 910 nm in the Pr3+:LiYF4 (Pr:YLF) laser crystal were registered and calibrated in unit of cross sections for the first time. Continuous-wave (CW) laser operation is demonstrated at 915 nm in π polarization by pumping the crystal with an optically pumped semiconductor laser (OPSL) at 479.2 nm. An output power of 218 mW is thus obtained with a laser slope efficiency of about 24% for an output coupler (OC) transmission of 1.9%. CW laser operation is also demonstrated at 907 nm in σ polarization by using a thin plate oriented at Brewster angle. An output power of about 89 mW with a slope efficiency of about 10% is then obtained for an OC transmission of 0.8%.The round-trip cavity losses are estimated for different experimental cavity configurations to be about 1% and the typical beam quality M2 factors measured in the transverse x and y directions are found equal to about 1.07 and 1.04, respectively. Finally, we also report on a double laser wavelength operation by using an OC with a transmission of about 0.05%, such effect resulting from joint-etalon effects inside the cavity.

Diode-pumped Pr3+:LiYF4 visible dual-wavelength laser

A diode-pumped simultaneous continuous-wave (cw) dual-wavelength Pr3+:LiYF4 laser in the green spectral region is experimentally demonstrated. We calculate the condition of gain-to-loss balance via an uncoated glass plane to achieve the simultaneous dual-wavelength operation. The simultaneous dual-wavelength Pr3+:LiYF4 laser at 546nm in π-polarization and 550nm in σ-polarization is experimentally realized. At an absorbed pump power of 1.5W, the maximum output power obtained at 546nm and 550nm is 184mW and 158mW, respectively.

Continuous-wave Pr³⁺:BaY₂F₈ and Pr³⁺:LiYF₄ lasers in the cyan-blue spectral region.

We report on the first, to the best of our knowledge, continuous-wave quasi three-level lasers emitting in the cyan-blue spectral range in praseodymium-doped crystalline materials. Applying Pr(3+):BaY2F8 as an active medium, up to 201 mW of output power at 495 nm could be obtained with a slope efficiency of 27% under pumping with an optically pumped semiconductor laser (2ω-OPSL) at 480 nm. In the same pumping scheme using Pr(3+):LiYF4, output powers up to 70 mW were realized at 491 and 500 nm, respectively. With Pr(3+):BaY2F8, diode-pumped laser operation with up to 11% slope efficiency and 44 mW output power was also achieved. In the latter case, detailed investigations on the temperature dependency of the laser output were conducted. Moreover, comparative experiments were carried out for the first time, to the best of our knowledge, with green-emitting Pr(3+):BaY2F8 lasers at 524 and 553 nm both under diode and 2ω-OPSL excitation.

Continuous-Wave Laser Emission of Pr:${\rm LiYF}_{4}$ at 695.8 nm

We present a diode-pumped Pr: LiYF4 (Pr:YLF) laser at 695.8 nm by suppressing the higher gain transitions near 640, 670, 698, and 721 nm. With an InGaN laser diode as the pump source, the output power of the laser centered at 695.8 nm in σ polarization was up to 51 mW, corresponding to a slope efficiency of 12.6% and a threshold power of 229 mW with respect to absorbed pump power. To the best of our knowledge, this is the first Pr:YLF laser emitting at 695.8 nm in σ polarization.

InGaN diode pumped actively Q-switched intracavity frequency doubling Pr:LiYF4 261 nm laser

We demonstrate actively Q-switched deep ultraviolet laser operation at 261 and 320 nm by intracavity frequency doubling of an InGaN laser diode-pumped Pr:LiYF₄ laser. We obtain a maximum peak power of 61.6 W (8.7 μJ/pulse at 7.7 kHz) and 594 W (19.0 μJ/pulse at 7.7 kHz) with a pulse width of 142 and 35 ns at 261 and 320 nm, respectively. The conversion efficiency from the fundamental laser energy at 639 nm to the second-harmonic generation is 88%. Good agreement is obtained with prediction by a rate equation model.

Tm3+ and Nd3+ singly doped LiYF4 single crystals with 3-5 \mu m mid-infrared luminescence

Mid-infrared (MIR) emissions of 2.4 and 3.5 m from Tm3+:LiYF4 single crystals attributed to 3H4->3H5 and 3H5->3F4 transitions as well as MIR emissions of 4.2, 4.3, and 4.5 \mu m from Nd3+: LiYF4 lasers attributed to 4I15/2->4I13/2,4I13/2->4I11/2, and 4I11/2->4I9/2 transitions, respectively, are observed. LiYF4 single crystals possess high transmittance of over 85% in the 2.5-6 \mu m range. The large emission crosssections of Tm-doped crystals at 2.4 \mu m (1.9\times 10-20 cm2) and Nd-doped crystals at 4.2 \mu m (0.84\times 10-20cm2) as well as the high rare-earth doping concentrations, excellent optical transmission, and chemicalphysical properties of the resultant samples indicate that Nd3+ and Tm3+ singly doped crystals may be promising materials for application in MIR lasers.

Continuous-Wave Ultraviolet Generation at 349 nm by Intracavity Frequency Doubling of a Diode-Pumped <formula formulatype="inline"><tex Notation="TeX">$\hbox{Pr:LiYF}_{4}$</tex></formula> Laser

We report a continuous-wave ultraviolet laser at 349 nm obtained by intracavity frequency doubling of a diode-pumped Pr3+-doped LiYF4 laser. Power scaling of lasers at 698-nm fundamental wavelength was realized using an InGaN laser diode with a maximum output power of 850 mW and a 5-mm-long 0.5 a.t. % laser crystal. The maximum output power at 698 nm was 215 mW. With beta barium borate crystal employed as the nonlinear medium, 33 mW of output power at 349 nm has been achieved.

Analyses of the thermal shifts of spectral lines in Nd3+-doped LiYF4 laser crystal

The red-shift of spectral line E-1(R-1 -> Y-2) and blue-shift of line E-2(R-1 -> X-5) with temperature in Nd3+-doped LiYF4 laser crystal are studied by considering both the static contribution due to lattice thermal expansion and vibrational contribution due to electron-phonon interaction. The study is based on the analyses of pressure and temperature dependences of these spectral lines. It is found that for both lines, the static and vibrational contributions result in the blue- and red-shift, respectively. So, the observed red-shift of line E-1 and blue-shift of line E-2 are due respectively to the static contribution being smaller and larger than the vibrational one. Also, we infer that the thermal shifts of lines E-3(R-1 -> Y-5) and E-4(R-2 -> Y-5) are very small because both contributions may be approximately canceled. When both the contributions are contained, whether the red-shift or blue-shift of a spectral line can be fitted with the almost same theoretical expression as that by including only the vibrational contribution used in red-shift in the previous papers if we change the expression concerning electron-phonon interaction coefficient.

Passively Q-switched Tm:YLF laser

Stable passive Q-switching of a Tm: LiYF4 laser is obtained using polycrystalline Cr2+: ZnS as a saturable absorber. The achieved maximum pulse energy of 0.9 mJ and peak power of 65 kW for a pulse duration of ∼14 ns represent substantial improvement and highest values for a passively Q-switched diode-pumped Tm laser operating at ∼1.9 μm.