Jitter reduction of the 729 nm clock laser for a Ca+ optical frequency standard

The electric quadrupole transition between the ground state and the first metastable state of a single Ca ion is an attractive choice for a frequency standard in the optical domain. Probing of the clock transition is carried out using quantum jump statistics which requires cycle times of several seconds. The spectral linewidth of the probe laser (local oscillator) must reach the hertz level for a duration at least as long as these cycle times. To reduce the TiSa laser linewidth at 729 nm, we use a KD*P electro-optic modulator (EOM) inside the laser cavity. This device shows a couple of mechanical resonances induced by piezo-electric ringing at frequencies larger than 50 kHz, limiting notably the use of the device for frequency corrections. Actual performances (Delta_v < 1 kHz for tau < 1 ms) of our laser set-up allow the observation of a preliminary spectrum with Zeeman splitting of the 729 nm transition of a single trapped Ca⁺ ion.