Repetition frequency control device

1. A repetition frequency control device comprising:

a slave laser that outputs a slave laser light pulse;

a slave photoelectric conversion unit that receives the slave laser light pulse, and converts the slave laser light pulse into a slave electrical signal;

a master laser that outputs a master laser light pulse;

a master photoelectric conversion unit that receives the master laser light pulse, and converts the master laser light pulse into a master electrical signal;

a frequency change unit that changes the repetition frequency of the master electric signal by a predetermined value;

a phase difference detector that detects a phase difference between the slave electric signal and the output from the frequency change unit; and

a loop filter that removes a high frequency component of an output from the phase difference detector, wherein:

the repetition frequency of the master laser does not undergo control based on one or both of the master electric signal and the slave electric signal; and

the repetition frequency of the slave laser light pulse changes according to an output from the loop filter.

2. The repetition frequency control device according to claim 1 , wherein the resonator length of the slave laser changes according to the output from the loop filter.

3. The repetition frequency control device according to claim 2 , wherein;

the slave laser comprises a piezo element;

the output from the loop filter is fed to the piezo element; and

the resonator length of the slave laser is changed by extension and contraction of the piezo element.