Hybrid fiber/bulk laser source designed for CO2 and wind measurements at 2.05†µm.

We present a hybrid fiber/bulk laser source designed for CO2 and wind monitoring using differential absorption LIDAR (DIAL) and coherent detection at 2.05 µm. This source features a master oscillator power amplifier (MOPA) architecture made of four fiber stages and one single-pass, end-pumped, bulk amplifier. This Letter focuses on the single-pass bulk amplifier performance and on the hybrid architecture benefits for DIAL and coherent detection. The bulk material is a holmium-doped YLF crystal that provides high efficiency amplification at 2.05 µm. This laser offers an energy breakthrough as compared to the classical stimulated Brillouin scattering (SBS) limit encountered in a fiber laser without compromising robustness, thanks to very few free-space optical elements and a small optical path. It delivers pulse energy and repetition frequency of 9.0 or 1.2 mJ/20 kHz with 200 ns quasi Fourier-transform limited pulses.

2.05-µm all-fiber laser source designed for CO2 and wind coherent lidar measurement.

This work reports on an all-fiber pulsed laser source for simultaneous remote sensing of CO2 concentration and wind velocity in the 2.05 µm region. The source is based on a polarization-maintaining master oscillator power amplifier (MOPA) architecture. Two narrow-linewidth master oscillators for ON-line/OFF-line CO2 differential absorption lidar operation alternately seed a four-stage amplifier chain at a fast switching rate up to 20 kHz. The MOPA architecture delivers laser pulses of 120 µJ energy, 200 ns duration (600 W peak power) at 20 kHz pulse repetition rate (2.4 W average power). The output linewidth is lower than 5 MHz, close to the pulse Fourier transform limit, and the beam quality factor is M2=1.12. The source also provides a pre-amplified 20 mW local oscillator with a relative intensity noise of -160dB/Hz that ensures optimal performance for future coherent detection.

Scanning wavefront folding interferometers.

We present modified scanning-type wavefront folding interferometers (WFIs), which allow spatial coherence measurements of non-uniformly correlated fields, where the degree of coherence is a function of two absolute spatial coordinates instead of coordinate separation only (Schell model). As an alternative to conventional prism-based WFI implementations, we introduce a scheme based on reflections by three mirrors. This setup allows us to avoid obstructions due to prism corners, and it is remarkably robust to polarization effects. Experimental results on measurement of fields that do not obey the Schell model are provided with the three-mirror WFI, and the results are compared to those obtained with a Young's interferometer realized using a digital micromirror device.