Optimization of error signal lineshape for modulation-free robust laser frequency stabilization

Abstract Frequency-stabilized external cavity diode lasers are essential components of precision quantum experiments. Atomic hyperfine states involved in such experiments are very sensitive to laser frequency drifts and thus the accuracy of the results is directly linked to the stability of the laser source. The quality of the error signal determines the lock performance of the laser source. An optimum error signal provides protection against mechanical vibration, laser intensity noise, and ambient magnetic field fluctuations. We have discussed the optimization of the error signal shape profile for 133 Cs D2 line, 6 2 S 1/2 F = 4 to 6 2 P 3/2 F’ = 4/5 crossover transition. For a non-optimum value, the peak-to-peak frequency drift is ∼ 8 MHz with the FWHM of the drift being 2.72 ± 0.3 MHz, whereas the FWHM for an optimized value is 436 ± 73 kHz showing a 6 times reduction. Also, the peak-to-peak frequency drift lies within 1.1 MHz measured for over 25 minutes which makes it suitable for use in high-precision spectroscopy and quantum experiments. Moreover, the optical layout allows possibility of further miniaturization which is quite crucial for field applications and deployable quantum sensors.