A time-resolved mid-infrared upconversion technique based on sum-frequency generation was applied to measure pulse propagation in λ ∼ 5.0 μm quantum cascade lasers operated in continuous wave at 30 K. The wavelength-dependent propagation delay of femtosecond mid-infrared pulses was measured to determine the total group-velocity dispersion. The material and waveguide dispersion were calculated and their contributions to the total group-velocity dispersion were found to be relatively small and constant. The small-signal gain dispersion was estimated from a measurement of the electroluminescence spectrum without a laser cavity, and was found to be the largest component of the total GVD. A negative group-velocity dispersion of β2 (=d2β/dω2) approximately - 4.6×10-6 ps2/μm was observed at the peak emission wavelength, and good agreement was found for the measured and calculated pulse-broadening.
All Science Journal Classification (ASJC) codes
- Atomic and Molecular Physics, and Optics