We demonstrate an optical parametric oscillator based on two HgGa 2 S 4 crystals with an extremely wide tuning range from 4.2 to 10.8 μm. The HgGa 2 S 4 optical parametric oscillator was pumped by a Q-switched nanosecond Nd : YLF laser at 1.053 μm. The absorption spectrum of ammonia was presented to demonstrate the feasibility of the developed optical parametric oscillator system for spectroscopic measurements and gas detection.

We report on the first BaGa 4 Se 7 nanosecond optical parametric oscillator pumped by Q-switched Nd:YLiF 4 laser at 1053 nm. The oscillator exhibits a pump threshold energy as low as 0.25 mJ. Midinfrared (MIR) idler wave tuning from 2.6 μm to 10.4 μm is demonstrated with an angle-tuned type-I (o-ee) y-cut sample, highlighting the superior performance of this novel large bandgap chalcogenide nonlinear crystal to generate tunable coherent radiation over its full MIR transparency range (0.47-18 μm). The phase-matching data are used to identify the most accurate dispersion relations of this compound among three recently published Sellmeier equations. Damage threshold measurements yielded values as high as 2.04 J cm −2 at 100 Hz pulse repetition rate, one of the largest among existing MIR χ (2) nonlinear materials.

A laser gas analyzer has been designed for determining the composition of exhaled air by means of photoacoustic spectroscopy. The analyzer, based on a broadband optical parametric oscillator and photoacoustic detector, provides high-precision rapid analysis of the multicomponent composition of human exhaled air for dynamic estimation of the efficiency of treating bronchus and lung diseases.

A human exhaled air analysis by means of infrared (IR) laser photoacoustic spectroscopy is presented. Eleven healthy nonsmoking volunteers (control group) and seven patients with chronic obstructive pulmonary disease (COPD, target group) were involved in the study. The principal component analysis method was used to select the most informative ranges of the absorption spectra of patients' exhaled air in terms of the separation of the studied groups. It is shown that the data of the profiles of exhaled air absorption spectrum in the informative ranges allow identifying COPD patients in comparison to the control group.

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