Intrinsic linewidth of quantum cascade laser frequency combs
Francesco Cappelli, Gustavo Villares, Sabine Riedi, Jerome Faist
TL;DR
This paper investigates the intrinsic linewidth of quantum cascade laser frequency combs, demonstrating that quantum noise limits the linewidth and that four-wave mixing correlates the noise of comb lines, with a measured linewidth of 292 Hz.
Contribution
It provides the first measurement of the quantum noise-limited linewidth of quantum cascade laser frequency combs and shows the role of four-wave mixing in noise correlation.
Findings
Linewidth of 292 Hz measured for 25 mW power
Quantum noise limit set by Schawlow-Townes formula
Four-wave mixing correlates quantum noise of comb lines
Abstract
The frequency noise power spectral density of a free-running quantum cascade laser frequency comb is investigated. A plateau is observed at high frequencies, attributed to the quantum noise limit set by the Schawlow-Townes formula for the total laser power on all comb lines. In our experiment, a linewidth of 292 Hz is measured for a total power of 25 mW. This result proves that the four-wave mixing process, responsible for the comb operation, effectively correlates the quantum noise of the individual comb lines.
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