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Publication: All-electrical frequency noise reduction and linewidth narrowing in quantum cascade lasers

An easy way of laser frequency noise suppression was developed in Alpes Lasers in cooperation with the University of Neuchâtel.

2014.11.10 | Celia Haldan Voetmann

Scheme of the experimental setup. LCE, laser control electronics (current driver and temperature controller); PA, preamplifier, bold arrows represent electrical current through the QCL.

Frequency noise PSD of the QCL measured in freerunning (A) and stabilized (B) conditions. The thin line above 100 kHz for the free-running QCL is an extrapolation of the 1∕f noise used for the linewidth determination. The “C” curve shows the frequency noise reduction achieved when stabilizing the QCL frequency to the side of the N2O transition using the same stabilization electronics and the optical signal from the MCT detector as an error signal. The corresponding full width at half-maximum (FWHM) linewidth of the laser calculated using the concept of the β-separation line [11] is also indicated in each case (at 10-ms observation time).

Simultaneous time series of the measured voltage, calculated electrical power and measured optical frequency fluctuations for the free-running (t < 10 ms) and stabilized (t > 10 ms) QCL.

Authors

Ilia Sergachev,1,* Richard Maulini,1 Alfredo Bismuto,1 Stéphane Blaser,1 Tobias Gresch,1 Yves Bidaux,1 Antoine Müller,1 Stéphane Schilt,2 and Thomas Südmeyer2

Affiliations:

1Alpes Lasers SA, 1-3 Max.-de-Meuron, CH-2001 Neuchâtel, Switzerland
2Laboratoire Temps-Fréquence, Institut de Physique, Université de Neuchâtel, CH-2000 Neuchâtel, Switzerland

*Corresponding author: ilia.sergachev@alpeslasers.ch

Abstract:

The method is based on observations that laser frequency fluctuations are highly correlated to voltage fluctuations measured on laser contacts in constant current mode. Therefore fast corrections of current calculated so that laser is kept in constant electrical power mode lead to frequency noise suppression.

The only additional components used for this method are voltage preamplifier and FPGA which calculates instant current corrections required to keep laser electrical power constant.

Different wavelength QCLs were used to demonstrate few times frequency noise suppression and linewidth narrowing. However, the technique can be generalized for other types of lasers and even other electrical devices where constant electrical power mode is preferable.

Reference: Optics Letters, Vol. 39, Issue 22, pp. 6411-6414 (2014)

Doidx.doi.org/10.1364/OL.39.006411

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