Room-temperature Fe:ZnSe laser tunable in the spectral range of 3.7-5.3 µm applied for intracavity absorption spectroscopy of CO2 isotopes, CO and N2O

Gain-switched Fe:ZnSe laser pumped by a coupled-cavity Q-switched Er:ZrF4 fiber laser

We report on a gain-switched operation of single-crystal Fe²⁺:ZnSe pumped by a coupled-cavity Q-switched Er³⁺:ZrF₄ fiber laser. With this approach, we use a continuous wave Er-doped ZrF₄ fiber laser whose cavity is coupled with the Fe:ZnSe laser cavity. A stable Q switching operation of the Er-doped fiber laser was achieved in this case and, as a result, a gain-switched operation of the Fe:ZnSe laser was obtained. The highest repetition rate was 79 kHz, the pulse duration of the pump Er-doped laser was ∼1.6 μs, and the pulse duration of the Fe:ZnSe was 62 ns. The maximum output power achieved from gain-switched Fe:ZnSe was 63 mW.

Intracavity absorption spectroscopy of HCl isotopes, H2O, CH4, C2H4, and C2H6 in the 3.1-3.4 µm spectral range using a Cr:CdSe laser

We demonstrate the first application of a Cr:CdSe laser for highly-sensitive multicomponent intracavity absorption spectroscopy around λ = 3.1-3.4 µm. A detection scheme based on an integrated recording of multiple (∼70) individual Cr:CdSe laser pulses after a single pump-pulse excitation is reported. The sensitivity of our system corresponds to an effective absorption path length of L_eff ≈ 850 m. Exemplary measurements of atmospheric H₂O and CH₄, and additionally introduced gas-phase HCl, C₂H₄, or C₂H₆ are presented. The achieved noise-equivalent detection limits are in the ppb range. Possibilities for further sensitivity enhancement by up to a factor of 10⁴ are discussed.

Synthesis, Crystal Growth, and Annealing of CdSxSe1-x and Cr:CdS0.8Se0.2 Single Crystals

Mid-infrared laser in the 2-5 μm wavelength region is in the atmospheric transmission window range, and hence, it has important application prospects in the fields of optoelectronic countermeasures, space communication, environmental remote sensing, and molecular spectroscopy. One of the most promising technological approaches to achieve mid-infrared laser output is based on direct lasing of transition-metal (TM)-doped II-VI chalcogenide crystals. In this work, CdS_xSe_1-x and Cr:CdS_0.8Se_0.2 polycrystals were synthesized by a chemical vapor synthesis method from a stoichiometric mixture of vacuum-sublimed CdS and CdSe. The structure of the synthesized products was analyzed by X-ray diffraction (XRD). Using these synthesized products, CdS_xSe_1-x and Cr:CdS_0.8Se_0.2 single crystals were grown by the physical vapor transport (PVT) method. After annealing, the band gap becomes smaller and the transmission range widens to 17 μm. The composition of the single crystals was determined by energy-dispersive spectrometry (EDS) mapping and XPS, and it was found to be uniform throughout the ingot. In addition, the absorption peak maximum for the Cr²⁺ ion in the Cr:CdS_0.8Se_0.2 crystal is at 1.84 μm.

Passively Q-switched 5-µm Ce3+-doped selenide glass laser using Fe:CdTe and Fe:CdSe as saturable absorbers

The first, to the best of our knowledge, mid-infrared Q-switched Ce³⁺-doped glass laser is demonstrated. As saturable absorbers, Fe²⁺:CdSe and Fe²⁺:CdTe are used for the first time. When Q-switched by Fe:CdSe, the laser operates in a multi-pulse regime with an individual pulse width of 110 ns, centered at λ = 5.20 µm. With Fe:CdTe as saturable absorber, 1-3 giant pulses of 30 ns pulse width are generated at λ = 5.13 µm.

Study of a Mode Separation Due to Polarization Existing in a Cavity-Enhanced Absorption Spectroscopy

A special phenomenon of resonance mode separation is observed during the study of a high sensitivity folded-cavity enhanced absorption spectroscopy for the measurement of trace gases. The phenomenon affects the measurement of gas absorption spectrum in the cavity. This resonant mode separation phenomenon of the resonant cavity is different from the resonant modes previously observed in linear-cavity enhanced absorption spectroscopy systems. To explore the mechanism of this phenomenon, a series of hypotheses are proposed. The most likely reason among these hypotheses is based on the different reflectance properties of the plane mirror at the fold of the cavity for S-polarized light and P-polarized light. Based on the matrix calculation method, the different reflectance and phase shift of the plane mirror for S-polarized light and P-polarized light are analyzed theoretically, and the results are in better agreement with the phenomena observed in the experiment. Finally, in order to eliminate the resonant mode separation phenomenon, line polarizers were added. By improving the system, the cavity enhanced absorption spectrum of residual water vapor in the cavity was successfully measured, and a minimum detectable absorption coefficient of α_min = 7.6 × 10⁻⁹ cm⁻¹ can be obtained in a single laser scan of 10 s.

Mid-infrared laser performance of Ce3+-doped selenide glass

An extensive study of a novel room-temperature mid-infrared Ce³⁺-doped Ge₂₀Sb₁₀Ga₅Se₆₅ glass laser is reported. An influence of output-coupler transmission on laser efficiency and emission spectra is investigated. Pumped by a pulsed Fe:ZnSe laser at 4.1 µm, a maximum output energy of 35 mJ is demonstrated at 5.2 µm, with a laser threshold of about 60 mJ and a slope efficiency of 21%. The tuning range of a mid-infrared Ce:glass laser is reported for the first time: with an intracavity prism, the laser is continuously tunable in the spectral range of 4.5-5.6 µm. The internal losses are determined to be below 9% per roundtrip.