This kind of laser pointer has the big size

This kind of laser pointer has the big size
Issued by the laser a laser beam by the cylindrical lens 2 and 3 expansion, by the film surface and the edge edge of a slit width of the incident light beam irradiation. For ease of installation was seized film edge margin of the film surface to stagger a certain distance; adjusting the cylindrical lens 2 and 3 of the distance between the slit diffraction of light focused at a predetermined distance, 16 diffraction fringes perpendicular to the narrow seam started; photodetector 14 photodiode, placed in a given location, the intensity of the diffraction fringe signal is transformed into electrical signals, and the amplifier 13, the display monitor 10. Generally select the second or third level of dark stripes as a test positioning stripes. Adjust the edge margin of 7 to change the width of the positioning stripes into the photodiode. For the quantity of laser pointer is large. 
Laser interferometer to produce interference fringes change frequency and measuring the velocity of the mirror, from rest to exercise and then back to the stationary process corresponds to the frequency from zero to a maximum and then return to zero the whole process, and therefore light intensity transformed into a DC signal frequency range is from scratch. This signal can only DC amplifier to amplify. However, the interference of the external environment, the average intensity of interference fringes will be great changes that caused the error count. Laser interferometer anti-interference ability is poor, can only be used under the thermostat anti-vibration conditions. In order to overcome these shortcomings, the introduction of a certain frequency carrier signal of the interferometer. It is the procedure of performing the sampling inspection of laser pointer .Measurement principle of laser diffraction. Phenomenon of light diffraction, the position relationship between the diffraction and the observation of the diffraction fringe of the screen (ie, the diffraction field) is generally divided into two types: Fresnel diffraction and Fraunhofer diffraction, the former is the diffraction phenomenon of the limited distance , the observation of the small screen to the distance of the diffraction, also known as near-field diffraction. The latter is an infinite distance at the diffraction phenomenon can be observed in the viewing screen from the diffraction can be approximated by infinity, also known as the far-field diffraction. Because the conjugate surface of the lens back focal plane at infinity, so the lens can be accurately observed the Fraunhofer diffraction. Lens diffraction measurement system has been widely used.