7 November 2005 Femtosecond seeded 150 nm-bandwidth optical parametric amplifier for active imaging applications at 1550 nm
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Abstract
Laser ranging and burst illumination imaging (BIL) in the atmospheric transmission window at 1.5μm are made difficult by speckle effects which are observed when a rough surface is illuminated by a laser beam with a coherence length greater than the characteristic surface feature size. For the narrowband pulsed lasers currently used, this length is of the order of a few millimetres which leads to observable speckle effects for many common surfaces. In this context we describe progress towards the development a short-coherence length laser source operating at 1.5μm and based on optical parametric amplification of broadband seed pulses from a modelocked femtosecond erbium-doped fibre laser. Our optical parametric amplifier (OPA) system comprises a compact actively Q-switched 1047nm Nd:YLF laser, operating at ~1kHz repetition frequency, to which a 54MHz femtosecond 1.55μm Er:fibre laser is synchronised. The fibre laser produces bandwidth-limited 100fs pulses which are stretched by chromatic dispersion in a spool of SMF28 fibre to match the 3.5ns duration of the Q-switched pulses. Pulses from the Nd:YLF and Er:fibre lasers act as the pump and seed respectively for an OPA based on an aperiodically-poled crystal of MgO:PPLN containing a single linearly chirped grating. The chirp grating enables broadband parametric amplification across a wavelength range comparable with the spectral bandwidth of the seed pulses, amounting to ~150nm in the wings of the spectrum. Early results from this system have demonstrated output energies of 2.55μJ and a single-pass gain ~51dB and are expected to be increased with continued development of the project.
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Karl A. Tillman, Karl A. Tillman, Derryck T. Reid, Derryck T. Reid, } "Femtosecond seeded 150 nm-bandwidth optical parametric amplifier for active imaging applications at 1550 nm", Proc. SPIE 5989, Technologies for Optical Countermeasures II; Femtosecond Phenomena II; and Passive Millimetre-Wave and Terahertz Imaging II, 59890R (7 November 2005); doi: 10.1117/12.630687; https://doi.org/10.1117/12.630687
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