06-05-2011, 09:24 AM
Solidstate lasers can produce lightin red and blue parts of the visiblespectrum, generating laserlight in all colours except green. Butrecent research work suggests thatthis ‘green gap’ could be plugged.New techniques for growing laserdiodes could soon make brilliant fullspectrumdisplays a reality.Plugging the green gap in the redgreen-blue triad needed for full-colourlaser projection and display wouldhelp speed the introduction of laserprojectors for televisions and movie theatres, which will display much richercolours than other systems, and tinyhandheld projectors as in cellphones.High-power green diodes might be employed in such applications as DNAsequencing, industrial process controland underwater communications.The familiar green laser pointersused by lecturers employ a complicatedtwo-step process to generatelight. Semiconductor lasers inside thesedevices emit infrared radiation havinga wavelength of around 1060 nanometres.This radiation then pumpsa crystal that oscillates at half thiswavelength—530 nanometres, whichcorresponds to green part of the spectrum.The process is costly, inefficientand imprecise; the second crystal canheat up, altering the wavelength of theresultant green light. Lasers that generategreen light directly would avoidthis problem.
Multiquantum-wellfundamentals
Fig. 1 shows the scheme of a homojunctionlaser where a single p-njunction is formed from only a singlecrystalsemiconductor material. Thereis a highly reflective surface at oneend and a partially reflective surfaceat the other end. The p-n junction isforward-biased by an external voltagesource. As electrons move through thejunction, recombination occurs just asin an ordinary LED light emitter.To achieve laser action, it is necessaryto contain photons within thelaser medium and maintain the conditionsfor coherence.
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http://www.electronicsforuelectronicsfor...sp?id=4210
Multiquantum-wellfundamentals
Fig. 1 shows the scheme of a homojunctionlaser where a single p-njunction is formed from only a singlecrystalsemiconductor material. Thereis a highly reflective surface at oneend and a partially reflective surfaceat the other end. The p-n junction isforward-biased by an external voltagesource. As electrons move through thejunction, recombination occurs just asin an ordinary LED light emitter.To achieve laser action, it is necessaryto contain photons within thelaser medium and maintain the conditionsfor coherence.
Download full report
http://www.electronicsforuelectronicsfor...sp?id=4210