Quantum cascade lasers tuned by amorphous As₂S₃ claddings

Quantum cascade lasers (QCLs) have become a key component in the development of optical approaches to sensing applications. Recent experiments have shown the ability to achieve second harmonic generation from these structures suggesting the possibility of achieving short wave-infrared output. However, in these cases the power of the non-linear mode is limited by its phase mismatch with the fundamental cavity mode. By modifying the effective index of the laser system through cladding, one may ameliorate the mismatch to increase power output. In this study, we develop a simple method for drop-coating arsenic sulfide (As₂S₃) glass on QCLs. The glass is processed by above band-gap illumination, which induces a change in the refractive index resulting in a shift of the output mode of the laser. We observe the effective index to change by a factor 1.3 × 10^-4 after 20 minutes of illumination at 312 nm for the fundamental wavelength of the QCL. Below band-gap irradiation, such as that occurring during device operation, is confirmed to have no effect on the material. Studies of the output of QCLs reveal for the first time mode shifting of the spectra as a result of optical modification to a cladding layer.