Poster De Conférence Année : 2024

100 µs - 100 Hz coherent beam combining of laser amplifiers for Fourier transform acousto-optic imaging

Résumé

High-resolution optical imaging of highly scattering medium at large depths (> cm) is demanded by multiple medical applications. Fourier-transform acousto-optic imaging (FT-AOI) is a hybrid technique that couples ultrasonic waves (US) to infrared laser light: photons that cross a US-pulse path are tagged and selectively detected. The penetration depth is currently limited by the optical peak power available from single-frequency diode laser devices. Coherent beam combination, based on the constructive interference of multiple coherent laser beams, can improve the laser source power while preserving its beam quality and spectral purity. We describe a diode-laser-based source for an AOI architecture, based on a parallel master-oscillator / power-amplifier configuration. A narrow-linewidth CW-operated single-frequency laser diode at 828 nm injects two pulse-pumped tapered semiconductor optical amplifiers (TSOAs) with a 100 µs pulse duration and a 100 Hz repetition rate. The amplified beams behind the TSOAs are coherently superposed on a 50:50 beamsplitter. The combined peak power is actively stabilized by correcting the optical path length difference between the two arms with a piezoelectric element. The combined peak power reaches 8.9 W with a combining efficiency > 83 %. The phase drift during the pulse as well as the spatial profile evolution have been carefully characterized and do not affect the combining efficiency. The time-peak power during 1 hour of measurements has a fluctuation of only 1.3 %, which is significantly better than the free-running system. The laser source is implemented in a fully functional integrated FT-AOI architecture based on digital holography coupled with spatio-temporally structured ultrasound-plane waves. An increase of the infrared optical laser power and high-speed-parallel GPU processing allows us to achieve real-time imaging (~Hz). The first images obtained by AOI through a scattering medium (reduced scattering coefficient: 10 cm-1, width: 2 cm) mimicking biological tissues will be presented.

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Dates et versions

hal-04893020 , version 1 (17-01-2025)

Identifiants

Citer

Qin Liu, Sylvie Janicot, François Figliolia, François Ramaz, Jean-Michel Tualle, et al.. 100 µs - 100 Hz coherent beam combining of laser amplifiers for Fourier transform acousto-optic imaging. Unconventional Optical Imaging IV, Apr 2024, Strasbourg, France. SPIE, pp.68, ⟨10.1117/12.3016635⟩. ⟨hal-04893020⟩
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