
INTERFERENCE 221
the cavity length. If the frequency is too high, the opposite effect occurs. When the laser is
operating at the peak, then the signal decreases when the oscillator output is either positive or
negative. The output of the mixer is zero, and no correction occurs.
7.5.4 Frequency Modulation
In Section 7.3.4, we discussed the ability to make distance and velocity measurements using
a chirped or frequency-modulated (FM) laser. Now that we understand how the frequency of
a laser is determined, we can discuss the use of an electro-optical modulator to produce the
frequency modulation. In Section 6.5.2, we discussed using an electro-optical ...