The theater laser projector was built around a Spectra-Physics model 164 ion laser back in the early 1970s. Designers realized that special output mirrors could be used to allow lasing to occur simultaneously at red, yellow, green, and blue wavelengths. The raw beam, a beam that appeared white to the eye, was shot with a high refractive-index prism, which achieved a separation of about two degrees between blue and red. It was with this technology that the laser projector was created.
The original laser projection system was put into an enclosed relay rack cabinet of approximately 2 1/2 feet (about 0.76 meters) square by 6 feet (about 1.83 meters) tall. Needless to say, the first laser projector was huge as compared to today’s laser projector. A ½ inch (1.27 centimeters) thick aluminum plate sectioned off the cabinet of the original laser projector. The laser head, which was 4 feet (about 1.22 meters) long, was mounted vertically on one side of the plate. The laser head pointed downward.
The laser beam of the laser projector was then reflected through a hole to the opposite side of the plate. The projector's optical equipment was mounted on that side. The white laser beam was refracted into its component colors by a prism, which is a piece of glass or quartz-like material that reflected the beams. The four individual colored beams were then reflected through four acousto-optic modulators (AOMs), which forced the intensity of the individual beams to be varied electronically. This varied the frequencies from DC to more than 5 kHz depending on the need.
The very first image produced by a laser projector was not well defined. With the changes that have been made to the basic laser projector over the years, however, the laser projector is now the heart of any graphics system.
Most full-color projectors use polychromatic AOMs (PCAOMs). These control the blanking and color selection in the laser projector. They are usually used with what is referred to as "white-light" beams to create full-color graphics. The new type of laser projector is capable of doing things that the original creators never fathomed.
With this type of laser projector, a white-light laser beam enters the PCAOM crystal from the right, while a radio-frequency (RF) signal is injected from the top. The RF signal sets up a diffraction pattern, which acts as a prism.
A laser projector is basically sound and light playing together. The result is two beams exiting on the left and becoming the desired color. There is also a "waste" beam containing all of the colors except the desired color. Together, these light beams can create any image desired.
