Wednesday, December 18, 2013

The Working Of An RGB Laser

By Cornelia White


A laser that emits three primary colors, red, green and blue is an RGB laser, the name coming from the three primary colors. These can be emitted in a single beam for all the three colors or a separate beam for each of the color. Through additive mixing which involves combination of the three basic colors at different frequencies, a number of several other colors can be obtained.

RGB lasers are being exploited as an alternative to arc lamps sources (beamers). Although arc lamps have been used for a long period as a source of beams particularly because they are much cheaper, they suffer from setbacks such as limited lifetime, high wall-plug efficiency is impossible, poor image quality as a result of poor spatial coherence and the fact that available color space is not wide enough. For this reasons, the former is becoming more popular RGB sources are much more popular.

These types of lasers achieve coherence of wavelengths, a reason why they outperform many other sources of beams. The coherence is on both time and space allowing for inferences. The consistency in the change of phase properties over a long distance results into high quality images that make them preferred for entertainment and other professional applications.

The narrow optical bandwidth of the three types of beams produced put them close to monochromatic beams, a property that makes them able to produce very sharp and clear images on color mixing. For this reason, their applications are increasing, not forgetting the use in cathode tubes, lamp based beamers, color printers and many types of projectors.

These beamers however are known to emit beams that are low in power. With cinema projectors requiring over 10 W of power per color, the use of RGB sources is limited. In addition to power insufficiency, there other challenges include maturity and cost effectiveness. There is also a need of better quality of beam for efficient working of these beamers.

External optical modulators are normally used in these types of beamers although RGB sources are fitted with power-modulators for better signals in situations where the optical modulator use is made impossible as a result of low power miniature devices. Laser diodes for instance are used to achieve modulation bandwidth between 10 to 100 megahertz or even much higher resolutions.

The red, green and blue lasers come in several types depending on the design and construction. One method involves the use of three different types of lasers with each emitting beam of a particular color. These forms of visible beam lasers are however not as suitable as the non visible ones that are near infrared in nature.

The other method is the use of an infrared solid-state laser where a single near-infrared laser generate a single color that then undergoes through different stages of nonlinear frequency conversion to produce the three colored beams. There are many other schemes of producing the desired wave lengths such as through combination of parametric oscillators, some frequency mixers and even frequency doublers in addition to other methods.

Technological advancements opens windows for development of a better RGB laser that is capable of overcoming most of the challenges associated with the existing ones. With this possibility, these lasers are predicted to replace all other forms of lasers.




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