Narrow laser linewidth measurement with the optimal demodulated Lorentzian spectrum: erratum.

This erratum corrects errors in Fig. 4(b) of the original paper, Appl. Opt.63, 1847 (2023)APOPAI0003-693510.1364/AO.510265. This correction does not affect any of the results or conclusions of the aforementioned paper.

Narrow laser linewidth measurement with the optimal demodulated Lorentzian spectrum.

A method called the optimal demodulated Lorentzian spectrum is employed to precisely quantify the narrowness of a laser's linewidth. This technique relies on the coherent envelope demodulation of a spectrum obtained through short delayed self-heterodyne interferometry. Specifically, we exploit the periodic features within the coherence envelope spectrum to ascertain the delay time of the optical fiber. Furthermore, the disparity in contrast within the coherence envelope spectrum serves as a basis for estimating the laser's linewidth. By creating a plot of the coefficient of determination for the demodulated Lorentzian spectrum fitting in relation to the estimated linewidth values, we identify the existence of an optimal Lorentzian spectrum. The corresponding laser linewidth found closest to the true value is deemed optimal. This method holds particular significance for accurately measuring the linewidth of lasers characterized as narrow or ultranarrow.

Simple, low-cost, and well-performing optical phase-locked loop for frequency and phase locking of semiconductor lasers.

We demonstrate a simple, low-cost, and well-performing optical phase-locked loop (OPLL) circuit with ADF4007 as the phase frequency detector chip to achieve frequency and phase locking of two semiconductor lasers in both short and long terms. The measured short term performances, determined by fast feedback, show that the spectral width of the beat signal is low, around 1 Hz, and the residual phasing error is 0.04r a d 2. The measured long term performances, determined by slow feedback, show that the drift of the central frequency of the beat signal is within 1.1(1) Hz in 2 h, and the derived Allan deviation is less than 0.4 Hz within all integration times of up to 1000 s. The phase noise measurement shows a suppression of phase noise of the beat signal from free running to closed-loop OPLLs in a Fourier frequency of 10 Hz-20 kHz. These measurements show that the OPLL circuit we modified can fit most scientific experiments requiring a fixed frequency difference and phase coherence.

Tunable laser frequency lock based on a temperature-dependent Fabry-Perot etalon.

A simple method for laser frequency stabilizing by a temperature-tuned Fabry-Perot etalon is reported. The etalon is a plano-convex lens that permits tuning the length and refractive index via controlling the temperature for shifting wavelengths in the region of 852 nm, with a transmission spectral linewidth of ∼72.5MHz and free spectral region of ∼16GHz. Using this scheme, arbitrary frequency locking of a laser with an adjustable frequency resolution of 2.34GHz/∘C is realized, and MHz-level long-term stability is demonstrated.

Application of sub-Doppler DAVLL to laser frequency stabilization in atomic cesium.

We achieve laser frequency stabilization by a simple technique based on sub-Doppler dichroic atomic vapor laser lock (DAVLL) in atomic cesium. The technique that combines saturated-absorption spectroscopy and Zeeman splitting of hyperfine structures allows us to obtain a modulation-free dispersion-like error signal for frequency stabilization. For the error signal, the dependence of peak-to-peak amplitude and the slope at the zero-crossing point on the magnetic field is studied by simulation and experiment. Based on the result, we obtain an available sub-Doppler DAVLL error signal with high sensitivity to the frequency drift by selecting an appropriate strength of the magnetic field. Ultimately, the fluctuation of the locked laser frequency is confined to below 0.5 MHz in a long term, exhibiting efficient suppression of frequency noise.