Research on Mid-Infrared Parametric Oscillators - Part 02

1. Introduction

With the rapid development of fiber pulse lasers, fiber pulse lasers are widely used in OPO technology. Compared with all-solid-state lasers, fiber lasers have the advantages of flexible and compact structure, high reliability, good beam quality and low cost, and have become the preferred choice for pumping MgO:PPLN crystals (www.wisoptic.com) in mid-infrared laser system. In 2010, KOKABEE et al. used a 1064 nm fiber laser to pump MgO:PPLN crystal and achieved a 3.08 μm laser output of 4.9 W. In 2012, LIN et al. used a narrow linewidth pulsed fiber laser with a central wavelength of 1060 nm to pump MgO:PPLN and achieved a maximum of 5.5 W. 3.82 μm mid-infrared laser output; in 2021, Chen Bingyan of Changchun University of Science and Technology used a narrow linewidth 1064 nm fiber laser as the pump source. When the pump power was 18.1 W, a 3822.5 nm laser output of 2.06 W was obtained; in 2023, Ge Jinzhu of Changchun University of Science and Technology and others used linear polarization narrow linewidth The 1065 nm fiber laser pumped the external cavity MgO:PPLN-OPO and obtained a 3.44 μm laser output with a maximum output power of 3.536 W.

This paper uses a wide spectrum 1 μm fiber pulsed laser to pump a MgO: PPLN crystal under the operation mode of DPSR-OPO (double-pass pumping beam, signal beam single resonance) , at the wavelength of 3817 nm, to acquire a maximum output power of 5.93 W.

2. Experimental Setup

The mid-infrared laser used in this paper consists of an all-fiber pulse laser and an OPO system. Among them, the all-fiber pulse laser adopts the MOPA structure, experimental device diagram is shown in Figure 1. The seed source consists of a highly reflective grating (FBG HR), an acousto-optic modulator (AOM), a ytterbium-doped double-clad fiber (YDF), a pump-signal combiner, and a low-reflection grating (FBG-OC). The output power is 1.1 W, and the repetition rate

is 150 kHz, and the pulse width is 78 ns. The power amplification stage consists of two stages of amplification, both of which are pumped by a 915 nm semiconductor laser (LD). Among them, the first-stage power amplifier uses YDF with a core diameter of 20 μm and a cladding diameter of 130 μm, to make an output power of 9.5 W; The second-stage power amplifier uses YDF with a core diameter of 30 μm and a cladding diameter of 250 μm. To prevent the backward light and the amplified spontaneous emission to damage to front devices, an isolator is added between the seed source, the first-stage power amplifier, and the second-stage power amplifier. The 1064 nm laser which undergoes 2 level amplifying emits through an ISO collimator.