Abstract
The frequency-noise power spectral density of a room-temperature distributed-feedback quantum cascade laser emitting at λ = 4.36 μm has been measured. An intrinsic linewidth value of 260 Hz is retrieved, in reasonable agreement with theoretical calculations. A noise reduction of about a factor 200 in most of the frequency interval is also found, with respect to a cryogenic laser at the same wavelength. A quantitative treatment shows that it can be explained by a temperature-dependent mechanism governing the transport processes in resonant tunnelling devices. This confirms the predominant effect of the heterostructure in determining shape and magnitude of the frequency noise spectrum in QCLs.
Highlights
The interest of the scientific community in frequency-noise properties of quantum-cascade lasers (QCLs) is growing in parallel with increasing demand of such sources for high-resolution spectroscopy and frequency metrology.Cryogenically-operated QCLs have demonstrated a very low intrinsic linewidth [1], related to the white-noise component of their frequency noise spectrum
The frequency-noise power spectral density of a roomtemperature distributed-feedback quantum cascade laser emitting at λ = 4.36 μm has been measured
A small intrinsic linewidth, for its own sake, does not necessarily mean that the QCL emission can be narrowed: when its frequency noise spectrum is well behaved at lower frequencies, locking loops with only moderate gains and bandwidths are needed to achieve narrow linewidths and low energy content in the wings of the emission spectrum
Summary
The interest of the scientific community in frequency-noise properties of quantum-cascade lasers (QCLs) is growing in parallel with increasing demand of such sources for high-resolution spectroscopy and frequency metrology.Cryogenically-operated QCLs have demonstrated a very low intrinsic linewidth [1], related to the white-noise component of their frequency noise spectrum. The operating temperature of the device was already predicted [6] to play a key role for the frequency noise of the laser, since several mechanisms contributing to noise (such as carrier transport processes in resonant tunnelling heterostructures) are expected to depend on frequency, as well as on the specific heat of the QCL. This latter quantity, in particular, is expected to affect FNPSD, as it eventually sets a thermal cut-off for the dissipative currentto-frequency-conversion mechanisms occurring in the laser, affecting the current-related portion of the noise spectrum. From this point of view, the comparative measurements of the FNPSD of two QCLs operating at similar wavelengths but at two different temperatures (80 K and 290 K) offers a unique opportunity for testing the hypotheses outlined above
Sign-in/Register to view highlights & summary 
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call