Novel Broadband Amplifier for Mid-Infrared Semiconductor laser and applications in spectroscopy

Nano fabricated amplifier for semiconductor epitaxial laser A major challenge for building a widely tunable external cavity Mid-Infrared (MIR) laser using latest semiconductor epitaxial (epi) laser is to apply the Anti-Reflection (AR) coating that could turn the otherwise Fabry-Perot (FP) epi laser waveguide into an amplifier. As the epi laser waveguide are progressing rapidly in terms of tuning range [1, 2], the AR coating’’s bandwidth is becoming particularly challenging in the MIR because the change of the wavelength is quite large for a given tuning frequency. For example, as the tuning range of a quantum cascade laser is now reaching 400cm in the 7-11μm range, the AR coating is impossible to cover such wide range with a residual reflectivity much less than 1%. In this paper, we present an amplifier design that is nano-fabricated with Focused Ion Beam (FIB) [3]. The amplifier design is universal for semiconductor lasers, particularly useful in the MIR. A single layer broadband AR coating could further improve the performance of this amplifier design by further suppressing the FP modes and reduce the loss of the external cavity (EC) that build upon this amplifier.