Mid-infrared optical parametric oscillator pumped by a high-pulse-energy, Q-switched Ho³⁺:YAG laser

Abstract

A high-pulse-energy mid-infrared light source is presented, based on a zinc–germanium–phosphide optical parametric oscillator (ZGP OPO) pumped by an actively Q -switched high-pulse-energy H o 3 + : Y A G laser. The H o 3 + : Y A G pump laser source is capable of generating a pulse energy of 15 mJ from a single H o 3 + : Y A G rod at room temperature at a pulse repetition frequency (PRF) of 700 Hz. A maximum power of 20.1 W at a central wavelength of 2090 nm can be obtained in continuous operation, with a slope efficiency of 45.1%. A good beam quality with an M 2 better than 1.3 was achieved in Q -switched operation. The presented laser architecture was used as a suitable pump source for a ZGP-based OPO. Operated at a PRF of 2 kHz and pumped with a pulse energy of 8 mJ, a low conversion threshold of 1.5 W and a maximum total output power of 6.3 W could be obtained in a linear ZGP-based OPO. At maximum power, the peak power of the generated mid-infrared radiation exceeded 120 kW, while the beam quality was affected by the strong gain lens building inside the nonlinear material as a consequence of the high-energy pump pulses.

Q-switched Ho3+:YAG Porro resonators with improved alignment stability

“…The quasi-three-level laser material holmium-doped yttrium aluminum garnet (Ho 3+ :YAG) emitting at 2.09 µm can be used for important laser applications like material processing, atmospheric measurements, medical applications, and the nonlinear conversion into the mid-infrared wavelength range. [1][2][3][4] In principle, Ho 3+ :YAG is suitable to be used as laser material due to its long upper-state lifetime and high thermal conductivity and it can be pumped efficiently with Tm 3+ -doped fiber lasers at 1.908 µm resulting in a low heat generation. These properties enable a Q-switched operation with both high average power and energy.…”

“…These properties enable a Q-switched operation with both high average power and energy. 4,5 When a high mechanical stability of a laser is required, as for example in laser designators or rangefinders, 6 the concept of crossed Porro prisms as cavity end reflectors can be used. A Porro prism is a right-angled prism which behaves as a retroreflector in the plane which is perpendicular to its sharp apex.…”

A compact high power diode side-pumped 2.09 μm Tm,Ho:YAG laser

“…Operating within the eye-safe range of 2 µm, high-power, all-solid-state laser systems employing Ho-doped laser crystals provide considerable benefits in a wide range of applications, including remote sensing [1], material processing [2], and medical operations [3]. It is also a reliable pump source for optical parametric oscillators to produce mid-infrared and far-infrared radiation [4]. In addition to the need for highpower output, there is also a strong demand for compact and room-temperature-operated 2 µm laser systems.…”