Femtosecond Thin-Film Laser Amplifiers Using Chirped Gratings

[Image: see text] Ultrafast injection-locked amplification is achieved by sending femtosecond supercontinuum pulses into a polymeric thin film coated on a distributed feedback (DFB) microcavity consisting of chirped gratings. The spatial variation of the grating period led to the resonance of the DFB microcavity at different wavelengths for injection at different locations. This enables convenient and continuous tuning of the amplification spectrum by displacing the grating structures. The large area of the grating structures enabled large tuning range. The amplified spectrum can be continuously tuned from 545 to 580 nm through sliding the grating structures by about 3.5 mm. Sub-1 ps lifetime has been measured for the amplification process with a net amplification factor as large as 33. Injection locking enabled high-quality control of the divergence and transverse mode of the output laser beam.