Mid-infrared electronic wavelength tuning through intracavity difference-frequency mixing in Cr:ZnSe lasers.

Mid-infrared tunable coherent light sources are used in various laser applications, such as trace gas detection, laser processing, and biomedical diagnostics. This study demonstrates mid-infrared generation in the 8.3-11 µm (i.e., 900-1200 cm-1) spectral range by configuring intracavity difference-frequency generation (DFG) using ZnGeP2 (ZGP) in an electronically tuned Cr:ZnSe laser. The broad tunability is achieved with the maximum pulse energies exceeding 100 µJ by combining the electronic wavelength tuning with sligh angle adjustments (Δθ < 0.5°) of ZGP under the spectral noncritical phase-matching condition of the nonlinear material. The proposed DFG method is generalized to give access to a significant fraction of the molecular fingerprint region by utilizing selenide compounds (e.g., AgGaSe2, CdSe) in addition to ZGP, revealing the remarkable potential of ultrabroadband electronic mid-infrared scanning for numerous spectroscopic applications.

Parametric downconversion via vibronic transition.

This Letter presents the first, to the best of our knowledge, demonstration of noncritically birefringent-phase-matched parametric downconversion, which is associated with stimulated emission via vibronic transition in a laser gain medium. The so-called self-difference frequency generation is realized along the a-axis of a Cr:CdSe single crystal pumped by a Tm:YAG laser pulse at 2.013 µm, directly producing an infrared spectrum centered at 9 µm with the maximized effective nonlinearity. The light source, which benefits from the broad vibronic spectroscopic properties together with the wide transparency range of the host material, is expected to generate noncritically phase-matched, mid-infrared spectra beyond 20 µm along with birefringence engineering in the solid solution Cr:CdSxSe1-x.

Mid-infrared-scanning cavity ring-down CH2F2 detection using electronically tuned Cr:ZnSe laser.

The development of mid-infrared (mid-IR) tunable lasers has been driving various laser spectroscopic technologies. Herein, we report wavelength-scanning cavity ring-down spectroscopy (WS-CRDS) in the mid-IR region using an electronically tuned Cr:ZnSe (ET-Cr:ZnSe) laser, which could achieve a nanosecond pulse operation, with broad wavelength tuning of 2-3 µm. This allowed WS-CRDS-induced trace detection of the refrigerant, CH2F2. A CH2F2 detection limit of 0.66 ppm (3σ), and the detection of trace H2O in CH2F2 was realized using the broad wavelength-tuning range feature, demonstrating the effectiveness of the ET-Cr:ZnSe laser in WS-CRDS. We believe that our method would accelerate the development of various trace-gas detection technologies.

Non-destructive mid-IR spectroscopy with quantum cascade laser can detect ethylene gas dynamics of apple cultivar 'Fuji' in real time.

Many plants, including fruits and vegetables, release biogenic gases containing various volatile organic compounds such as ethylene (C2H4), which is a gaseous phytohormone. Non-destructive and in-situ gas sampling technology to detect trace C2H4 released from plants in real time would be attractive for visualising the ageing, ripening, and defence reactions of plants. In this study, we developed a C2H4 detection system with a detection limit of 0.8 ppb (3σ) using laser absorption spectroscopy. The C2H4 detection system consists of a mid-infrared quantum cascade laser oscillated at 10.5 µm, a multi-pass gas cell, a mid-IR photodetector, and a gas sampling system. Using non-destructive and in-situ gas sampling, while maintaining the internal pressure of the multi-pass gas cell at low pressure, the change in trace C2H4 concentration released from apples (Malus domestica Borkh.) can be observed in real time. We succeeded in observing C2H4 concentration changes with a time resolution of 1 s, while changing the atmospheric gas and surface temperature of apples from the 'Fuji' cultivar. This technique allows the visualisation of detailed C2H4 dynamics in plant environmental response, which may be promising for further progress in plant physiology, agriculture, and food science.

High-energy, nanosecond pulsed Cr:CdSe laser with a 2.25-3.08 µm tuning range for laser biomaterial processing.

We have developed a mid-infrared (mid-IR) tunable Cr:CdSe laser with nanosecond pulse operation. A broad tuning range from 2.25 to 3.08 µm and an output energy exceeding 4 mJ at 2.64 µm were demonstrated. The maximum energy conversion for absorbed energy reached 35% when the pump fluence was 2.1 J/cm2. We showed that Cr:CdSe is an attractive laser material for obtaining high-energy pulses in the mid-IR region and that the Cr:CdSe laser has high potential for laser biomaterial processing.

Dental hard tissue ablation using mid-infrared tunable nanosecond pulsed Cr:CdSe laser.

BACKGROUND AND OBJECTIVE: Mid-infrared erbium: yttrium-aluminum-garnet (Er:YAG) and erbium, chromium: yttrium-scandium-gallium-garnet (Er,Cr:YSGG) lasers (2.94- and 2.78-µm, respectively) are utilized for effective dental hard tissue treatment because of their high absorption in water, hydroxide ion, or both. Recently, a mid-infrared tunable, nanosecond pulsed, all-solid-state chromium-doped: cadmium-selenide (Cr:CdSe) laser system was developed, which enables laser oscillation in the broad spectral range around 2.9 µm. The purpose of this study was to evaluate the ablation of dental hard tissue by the nanosecond pulsed Cr:CdSe laser at a wavelength range of 2.76-3.00 µm. STUDY DESIGN/MATERIALS AND METHODS: Enamel, dentin, and cementum tissue were irradiated at a spot or line at a fluence of 0-11.20 J/cm2 /pulse (energy output: 0-2.00 mJ/pulse) with a repetition rate of 10 Hz and beam diameter of ∼150 µm on the target (pulse width ∼250 ns). After irradiation, morphological changes, ablation threshold, depth, and efficiency, and thickness of the structurally and thermally affected layer of irradiated surfaces were analyzed using stereomicroscopy, scanning electron microscopy (SEM), and light microscopy of non-decalcified histological sections. RESULTS: The nanosecond pulsed irradiation without water spray effectively ablated dental hard tissue with no visible thermal damage such as carbonization. The SEM analysis revealed characteristic micro-irregularities without major melting and cracks in the lased tissue. The ablation threshold of dentin was the lowest at 2.76 µm and the highest at 3.00 µm. The histological analysis revealed minimal thermal and structural changes ∼20 µm wide on the irradiated dentin surfaces with no significant differences between wavelengths. The efficiency of dentin ablation gradually increased from 3.00 to 2.76 µm, at which point the highest ablation efficiency was observed. CONCLUSION: The nanosecond pulsed Cr:CdSe laser demonstrated an effective ablation ability of hard dental tissues, which was remarkably wavelength-dependent on dentin at the spectral range of 2.76-3.00 µm. These results demonstrate the potential feasibility of the use of pulsed Cr:CdSe laser as a novel laser system for dental treatment. Lasers Surg. Med. 48:965-977, 2016. © 2016 Wiley Periodicals, Inc.

Electronically tuned Cr:ZnSe laser pumped with Q-switched Tm:YAG laser.

We demonstrated a Q-switched, Tm:YAG-laser-pumped electronically tuned Cr:ZnSe laser, which was equipped with an acousto-optic tunable filter as a wavelength-tuning element. A tuning range from 2.17 to 2.71 µm and a maximum output energy of 7.9 mJ at 2.41 µm were realized. The energy conversion efficiency reached 34.1% at 2.41 µm. In addition, the Cr:ZnSe laser produced a high-quality beam in the TEM(00) mode.