Home – Home – Jornals – Avtometriya 2023 number 1

We review our development of wavelength tuneable, high average power, picosecond-pulse, mid- infrared sources in the three micron widow for proposed application in tissue ablation studies and with the objective of source simplification and exploring the potential of all-fiber integration. Initial systems were based on difference frequency generation (DFG) of two synchronous master oscillator power fiber amplifier (MOPFA) schemes. The generated idler was tuneable over the range 3.28-3.45 µm, delivering greater than 3 W of average power, with a maximum pump to total DFG power conversion efficiency of 78 %. By simplifying the seed sources through synchronised in-line modulation of cw diode laser sources, more than 6 W was generated 3.31-3.48 µm with similar efficiency and with near diffraction limited beam quality (M2 = 1.4). In an improved and significantly simplified experimental configuration a source emitting around 3 µm was developed employing a novel χ⁽³⁾/χ⁽²⁾ cascaded nonlinear conversion architecture. Picosecond pulses from a 1.064 µm mode-locked Yb:fiber pump laser were used to generate 1.65 µm signal pulses through χ⁽³⁾ based four-wave mixing in a polarisation preserving photonic crystal fiber (PCF). The output of the PCF was then directly focused into a periodically poled lithium niobate crystal, generating idler radiation around 3 µm, with peak powers of ̴ 0.5 kW, via χ⁽²⁾-based three-wave mixing between the pump and signal pulses.