Yuting Huang, 2012, Physics

Charge instability has long been a known problem in traditional lasers. While high profile quantum cascade (QC) lasers are assumed to be stable, strong light instability is still observed in QC lasers at high currents. Finding the potential periodic behaviors in the light instability will help eliminate this instability and achieve QC lasers with optimal gain. During my internship, my group developed a MATLAB program to remotely control a QC laser and monitor up to 5,000 sequential light pulses at a fixed pulsed current each time. The light pulses revealed how the light output looks like in real time and showed that there are likely quasi-periodic light instability behaviors. We chose the region of instability on each pulse as the gate region, and calculated the average power output in the gate region for each pulse. We used fast fourier transform (FFT) to find the frequency components buried in these “noisy” data. Through this process, we have found more frequencies than we expected, and our frequency data vary between measurements. We are currently collecting more data for different lasers and are focusing on multiple positions on a light pulse instead of one gate region to avoid missing any information.