Comparative Analysis of FPGA based Systems and Indigenously developed Analog System for Frequency Stabilization of Lasers in NPLI-CsF1

Lasers and their stabilization to a particular hyper-fine transition of Cs-133 atoms is the back bone of the primary frequency standard (Cs fountain clocks). In CSIR-NPL we have indigenously developed primary frequency standard known as NPLI-CsF1 [1]. For the laser cooling of Cs atoms, ultra-stable laser frequency is required. A compact all-in-one laser frequency stabilization system has been designed which serves multiple objectives as it generates a square wave for modulating the laser current, provides lock-in amplification, enables us to monitor the derivative curve, to control the gain of system, and to produce and monitor the servo-control signal for providing feedback. This cost-effective and customizable analog locking system provide top-of-fringe locking with a phase-sensitive error signal corresponding to the Saturation Absorption Spectroscopy peaks of Cesium (Cs)-133 D2 line, which is fed back to the piezo of the laser for its frequency stabilization. The system provides stable frequency locking of laser for days at a stretch. Characterization and comparison of the circuit with FPGA based lock-in device has also been performed.