Mid-infrared (λ≈7.4µm) quantum cascade laser amplifier for high power single-mode emission and improved beam quality

A quantum cascade laser amplifier has been developed. It was used to obtain high power single mode emission at λ≈7. 4µm from a quantum cascade distributed feedback laser, together with enhanced beam quality. Laser and amplifier are directly coupled in a master oscillator power amplifier configuration. Peak optical powers of 0.5W at 80K have been obtained. Ninety percent of the total power is thereby emitted within a divergence of 20 in the lateral direction. The device showed single mode operation with a side mode suppression ratio of 30dB in the temperature range from 10 to 280K. This allowed tuning of the emission wavelength in the range from 7.36 to 7.46µm. The estimated peak amplifier gain is 6.4 and 4.9 dB at 80 and 300 K, respectively, and the cavity losses are 12.5 and 22 cm-1 at the corresponding temperatures.