Mid-Infrared Laser Generation of Zn1-xMnxSe and Zn1-xMgxSe (x ≈ 0.3) Single Crystals Co-Doped by Cr2+ and Fe2+ Ions-Comparison of Different Excitation Wavelengths.

Two different mid-infrared (mid-IR) solid-state crystalline laser active media of Cr2+, Fe2+:Zn1-xMnxSe and Cr2+, Fe2+:Zn1-xMgxSe with similar amounts of manganese or magnesium ions of x ≈ 0.3 were investigated at cryogenic temperatures for three different excitation wavelengths: Q-switched Er:YLF laser at the wavelength of 1.73 µm, Q-switched Er:YAG laser at 2.94 µm, and the gain-switched Fe:ZnSe laser operated at a liquid nitrogen temperature of 78 K at ∼4.05 µm. The temperature dependence of spectral and laser characteristics was measured. Depending on the excitation wavelength and the selected output coupler, both laser systems were able to generate radiation by Cr2+ or by Fe2+ ions under direct excitation or indirectly by the Cr2+→ Fe2+ energy transfer mechanism. Laser generation of Fe2+ ions in Cr2+, Fe2+:Zn1-xMnxSe and Cr2+, Fe2+:Zn1-xMgxSe (x ≈ 0.3) crystals at the wavelengths of ∼4.4 and ∼4.8 µm at a temperature of 78 K was achieved, respectively. The excitation of Fe2+ ions in both samples by direct 2.94 µm as well as ∼4.05 µm radiation or indirectly via the Cr2+→ Fe2+ ions' energy transfer-based mechanism by 1.73 µm radiation was demonstrated. Based on the obtained results, the possibility of developing novel coherent laser systems in mid-IR regions (∼2.3-2.5 and ∼4.4-4.9 µm) based on AIIBVI matrices was presented.

Revealing the peculiar local behavior of manganese and cobalt in diffusion-doped calcium orthovanadate Ca3(VO4)2.

Laser Ca3(VO4)2 single crystals (СVO; space group R3c, Z = 21) with crystallochemical formula Ca118Ca218Ca318Ca46(Ca5 + Са5А)3(V118V218V36)O168 grown by the Czochralski method were doped with Мn2O3 (CVO:Мn2O3) and Сo3O4 (CVO:Co3O4) by high-temperature diffusion annealing. Statistical and local structures were comprehensively studied by single-crystal and powder synchrotron X-ray diffraction and conventional single-crystal X-ray diffraction as well as by X-ray absorption spectroscopy for the first time. The presence of Mn(2+δ)+ ions with a mixed formal charge and Co2+ ions in the Ca2 (monocapped trigonal prism), Ca3 (two-capped trigonal prism), and Ca4 (octahedron) sites was revealed by diffraction methods. The tetrahedral coordination and the coordination intermediate between tetrahedral and octahedral were established for Mn(2+δ)+ and Co2+ ions, respectively. A fundamentally different structural behavior of dopant ions (concentration, formal charge, and coordination environment) in the CVO crystals doped with manganese in the form of Mn2O3 during the crystal growth or by high-temperature diffusion annealing was observed. The relationship between characteristic bands in the absorption, fluorescence, and excitation spectra of CVO:Мn2O3 and CVO:Co3O4 samples and transition metals with specific formal charges is discussed.

Long-pulse 4.4-4.6 µm laser oscillations of Fe2+ ions in a Zn1-xMnxSe (x = 0.3) crystal pumped by a 1940 nm Tm fiber laser through Cr2+ → Fe2+ energy transfer.

Millisecond-pulse laser operation of Fe2+ ions at 78 K is demonstrated in the Zn1-xMnxSe:Fe2+,Cr2+ (x=0.3) crystal under a Tm fiber 1940 nm laser pumping through a Cr2+→Fe2+ energy transfer process for the first time, to the best of our knowledge. The laser slope efficiency was 1% with respect to absorbed pumping energy at 1940 nm. The laser central wavelength shift from 4450 nm at 78 K up to 4510 nm at 110 K was observed. Tunability from 4350 up to 4670 nm at 78 K was achieved using an intracavity tuning element.

Influence of the pumping wavelength on laser properties of Fe2+ ions in ZnSe crystal.

ZnSe:Fe2+ active laser crystal properties at different excitation wavelengths (2.94 and 4.1 µm) were investigated, and noticeable variations of the fluorescence spectra shape and their maxima positions, as well as changes in decay times, were observed. A stepwise shift of the laser oscillation wavelength from 4.7 µm at 2.94 µm pumping to 4.95 µm at 4.1 µm pumping was achieved at room temperature.

Thulium fiber pumped tunable Ho:CaF2 laser.

The paper reports the first room-temperature operation of the in-band pumped Ho:CaF2 laser. A set of Ho:CaF2 crystals varying in holmium concentrations (from 0.1 up to 2.5 mol. % of HoF2), synthesized using the Bridgeman technique, was used for lasing and related spectroscopy investigation. A pulsed 1.94 µm thulium fiber laser system was used for Ho:CaF2 longitudinal pumping. For 1.5 mol. % of Ho:CaF2, the maximal wavelength tunability (from 2073 to 2114 nm) and output energy (1.6 mJ at 2113 nm) were obtained for absorbed pumping energy 34 mJ. Without the tuning element, the slope efficiency up to 30% in respect to absorbed power was obtained using this sample.

Dysprosium-doped PbGa2S4 laser generating at 4.3 µm directly pumped by 1.7 µm laser diode.

In this Letter, we demonstrate the pulsed and CW operation of the Dy:PbGa(2)S(4) laser directly pumped by the 1.7 µm laser diode. In the pulsed regime (pulse duration 5 ms; repetition rate 20 Hz), the maximum mean output power of 9.5 mW was obtained with the slope efficiency of 9.3% with respect to the absorbed pump power. The generated wavelength was 4.32 µm, and the laser beam cross section was approximately Gaussian on both axes. Stable CW laser generation was also successfully obtained with the maximum output power of 67 mW and the slope efficiency of 8%. Depopulation of the lower laser level by 1.7 µm pump radiation absorption followed by 1.3 µm upconversion fluorescence was demonstrated. These results show the possibility of construction of the compact diode-pumped solid-state pulsed or CW laser generating at 4.3 µm in the power level of tens mW operating at room temperature.

Diode-pumped Er:CaF2 ceramic 2.7 µm tunable laser.

Spectroscopic and laser properties of a newly developed high optical quality Er:CaF2 hot-formed ceramic were investigated. Under pulsed 968 nm laser diode pumping, the mid-infrared (2.7 µm) radiation was obtained with a slope efficiency of 3%. Laser tunability was reached using a birefringent filter and the laser tuning range of 118 nm, from 2687 up to 2805 nm, was demonstrated. The maximal output energy reached was 0.48 mJ at 2730 nm for the absorbed pumping energy 34 mJ.

Dysprosium-doped PbGa2S4 laser excited by diode-pumped Nd:YAG laser.

We realized a compact mid-IR room temperature operating Dy(3+):PbGa(2)S(4) laser, excited by a diode-pumped Nd:YAG laser at a wavelength of 1318 nm. The pumping laser was operating in pulsed mode with a pulse length of 4 ms and repetition rate of 20 Hz. Maximum pumping energy at a wavelength of 1318 nm was 15 mJ. Energy up to 90 µJ and mean output power of 1.8 mW was obtained at a wavelength of 4290 nm with a slope efficiency with respect to absorbed pumping energy better than 3%.

Demonstration of high self-Raman laser performance of a diode-pumped SrMoO4:Nd3+ crystal.

Passively Q-switched self-Raman laser oscillations in the SrMoO4:Nd3+ crystal optically pumped by a laser diode (LD) at 804 nm are demonstrated for the first time to our knowledge. Output parameters of LD-pumped SrMoO4:Nd3+ laser were investigated in free-running, passively Q-switched, and self-Raman regimes of laser operation, over a wide range of pulse repetition rates (8.5-85 kHz). A pulse energy of 21 microJ was measured in the self-Raman regime at 1163 nm (first Stokes) wavelength, which is 6 times higher than that for the GdVO4:Nd3+ self-Raman laser of similar design.

Oscillation properties of dysprosium-doped lead thiogallate crystal.

The room-temperature laser-oscillation properties of lead thiogallate crystals doped with dysprosium ions PbGa(2)S(4):Dy(3+) without additional codoping and codoped with potassium ion for excessive charge compensation were investigated. A slope efficiency of 1% was obtained for the codoped crystal. YAP:Er -1.66 microm laser resonant pumping of PbGa(2)S(4):Dy(3+) laser was compared with YAG:Nd -1.32 microm nonresonant pumping. The maximum energy obtained was 57 microJ with the negligible influence of the atmosphere.

Laser and self-Raman-laser oscillations of PBMoO4:Nd3+ crystal under laser diode pumping.

Different regimes of laser operation and stimulated Raman scattering (SRS) for a laser diode (LD)-pumped PbMoO4:Nd3+ crystal have been investigated. Under 1.5 W LD pumping, the output power of the PbMoO4:Nd3+ laser in the free-running mode at 1056 nm reached 0.65 W with a slope efficiency of up to 53%. Using different LiF: F-2 saturable absorbers, we achieved a maximum pulse energy of 11 microJ at a 1.4 ns pulse duration and a maximum output power of 0.35 W (10 microJ) at a 7 ns pulse width in the passively Q-switched mode. PbMoO4:Nd3+ self-Raman-laser operation at 1163 nm (first Stokes) was obtained for the first time, to our knowledge. The self-Raman-laser output pulse energy was measured to be as high as 6 microJ and the pulse duration was estimated to be shorter than 500 ps.