Narrow-linewidth, broadly tunable mid-infrared parametric source based on zinc germanium diphosphide crystals

Subject of study. A narrow-linewidth, broadly tunable mid-infrared (IR) parametric light source is investigated. The source consists of a singly resonant optical parametric oscillator (OPO) and an optical parametric amplifier (OPA) based on zinc germanium diphosphide nonlinear optical crystals, pumped by a repetitively pulsed Ho ³⁺ :YAG laser. Aim of study. This work aims to develop a source for generating broadly tunable repetitively pulsed mid-IR radiation with a narrow spectral linewidth and high pulse energy. Method. Narrow-linewidth OPO operation is achieved using an intracavity Fabry–Pérot etalon in the form of a silicon wafer with a thickness of 33 µm or 56 µm. Wavelength tuning in the mid-IR range is realized by varying the temperature of both the etalon and the nonlinear optical crystal. An OPA is employed to increase the pulse energy. Main results. Narrow-linewidth operation of the parametric source with a signal linewidth of 3–8 nm is demonstrated. Tuning is achieved over the ranges of 3860–4130 nm and 4210–4565 nm for the signal and idler waves, respectively. At a repetition rate of 10–50 Hz, the pulse energy reaches 1.7 mJ for narrow-linewidth radiation and 4.8 mJ in broadband (frequency-comb) operation. Practical significance. This high-power narrow-linewidth radiation source that is tunable over the range of 3.8–4.6 µm has potential applications in remote environmental monitoring, particularly for the detection of greenhouse gases such as CO ₂ and CO, as well as in wireless optical communication and in selective interaction with materials such as silicon and diamond.