In this work, we demonstrate a three-stage all-fiber master oscillator power amplifier (MOPA) system emitting over 40 W of continuous-wave (CW) output power at ~1.5 µm. The setup utilizes three self-fabricated high-power passive fiber components: a mode-field adaptor (MFA) and two types of pump and signal power combiners. Their development allowed us to become independent from commercially available components, which are often incompatible with fibers used in the experimental setups, resulting in additional losses. A power combiner with single-mode (SM) signal fibers in a configuration (5 + 1) × 1 was used in the second stage of the MOPA system, which was based on an SM Er–Yb co-doped double-clad (DC) fiber. The fabricated MFA was used to connect the second amplifier stage based on SM fibers with the third amplifier stage based on large-mode-area (LMA) fibers. In the third stage of MOPA system, based on Er–Yb LMA DC fibers, we used the fabricated power combiner based on LMA-type signal fibers in a configuration (6 + 1) × 1. The presented three-stage MOPA system, utilizing self-fabricated high-power passive fiber components, enables amplification of an input signal of 10 mW up to 44 W of the CW power at the wavelengths of 1555 nm and 1563 nm, corresponding to a gain level of approximately 36.4 dB.

We have developed a laser vibrometer based on an monolithic single-frequency green laser operating at 532 nm. This wavelength can be particularly useful in the case of underwater vibrometry, especially with regard to the minimum of water absorption for this wavelength range (blue-green window). Using polarizing optics, we proposed a configuration that allows the elimination of parasitic reflections at the air-glass-water boundary. A measurement of heterodyne signals as a mixing result of scattered and reference beams has been performed. The study was conducted in aqueous medium for the scattering waterproof paper and retro-reflective surface. In both configurations we have obtained signals with a relatively high S/N ratio > 20 dB (for scattering surface) and > 31 dB (for retro-reflective tape) with the Resolution Bandwidth RBW 10 kHz for a vibrometer output power of 5 mW and the distance to the moving object 1.2 m (including 0.3 m in air). In our opinion, laser Doppler vibrometry LDV based on high-performance single frequency solid-state lasers with a wavelength range corresponding to the blue-green window allows effective measurement of vibration in the underwater environment.

We present the module of booster amplifier for coherent beam combining Master Oscillator Power Amplifier (MOPA) system to operate with a narrow-linewidth seed laser. The goal was to achieve a highly modular system, manifested in the ease of changing the number of Coherent Beam Combining (CBC) channels. It uses a frequency tagging phase control scheme performed at acoustical frequencies, enabling a simple piezo fiber stretcher as actuating and tagging element and a cheap microcontroller to perform all the signal processing. The four-channel CBC system with the proposed booster module was built to verify our assumptions and the whole system’s performance.