This project is pursuing to build ultra stable lasers as local oscillators for optical clocks. Be...

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Ultra Stable Lasers

 

 

Summary:

This project is pursuing to build ultra stable lasers as local oscillators for optical clocks. Being the 'tick' source of the atomic clock, the local oscillator must maintain highly stable to ensure the performance of the atomic clock. We built reliable external cavity diode lasers which can be tuned in a wide range, and lock the laser frequency to an ultra stable Fabry-Parot cavity. The line-width of the laser is narrowed to Hz level by optical feedback from the cavity or high speed electronics with Pound-Drever-Hall method.

 

Description:

Any clock needs a 'tick' source. In an early mechanical clock, a pendulum gives the tick. The oscillating frequency of the pendulum is very low. In a cesium microwave clock, the tick source is a quartz oscillator which has a very high oscillating frequency (1010 ticks per second). In an optical clock, the tick source is a ultra stable laser. The laser frequency is super high (1014 ticks per second). With the fluctuation controlled at the same level, the optical clock will have a better relative stability. That is why we build optical clocks and ultra stable lasers.

 

The frequency of the laser is locked to an ultra high finesse Fabry-Parot cavity to remain stable. We use two approaches to lock the laser to the cavity. Firstly, we feed the transmission of the cavity back to the external cavity diode laser. The optical feedback can narrow the laser line-width down to several hundred Hertz. The second approach is to use Pound-Drever-Hall method to get a frequency error signal, and feed it back to the laser in terms of laser current and ECDL’s Piezo controlled cavity ‘length’through high speed electronics.

 

The 698nm laser line-width is measured to be 5Hz and the relative stability is 3E-15 at 1s. The performance of the laser will be further improved with our new design.