The phase method is to put one or more low frequency (relative to the light frequency modulation) in laser pointer pen, similar to the modulated audio signal in radio RF signal. The specific approach is: Using low frequency signal to control the output power of the laser, the laser reflection signal received power will change with the low frequency signal. Phase of the received signal and the output signal will be compared.
Due to the use of phase ranging laser pointer pen is a continuous output, the peak power is smaller, so the maximum distance is much smaller than the pulse method, usually non cooperative target maximum range of only a few kilometers, want to measure the distance to the moon is not possible.
Let laser pointer pen and photosensitive optical beam from a certain distance, so the measured points and lines that reflected light photosensitive unit and laser beam path will form an angle. This angle is measured, then according to the triangle of knowledge, we can calculate the measured point to photosensitive unit distance.
This is not the same light is relatively long, the laser pointer pen according to the sine wave modulation. The sine wave travels at the speed of light, the first 0 degrees behind some distance. What is the light emitted by the reflected light to the degree of the difference is the phase difference, on behalf of the distance (2 times).