Laser is the 20th century, following the atomic energy, computer, semiconductor, after another major human invention. The burning laser pointer has the characteristics of good direction, high brightness, good monochromaticity and so on. Its comprehensive performance is far more than that of traditional sunlight, incandescent lamp, fluorescent lamp, LED lamp and so on. It is a revolutionary way of using light information and energy. Since 1960, when Mayer invented the first laser (ruby lasers), laser technology has made great progress over the past 50 years and has achieved great success and played an important role in many areas of human society.
The development of laser technology is evolving from the early gas lasers (helium-neon lasers), high-power carbon dioxide lasers, excimer lasers, tunable dye lasers, semiconductor lasers, nanosecond and picosecond pulsed lasers to recent fiber lasers and femtosecond (Laser beam quality, pattern diversity, pulse width, peak power, average power, spatial coherence, temporal coherence, etc.) are increasing in all aspects of pulse high power laser and laser family members. The application of laser technology is becoming more and more extensive, has become an indispensable tool for scientific research, defense, military, lighting, optical fiber communication, information sensing, storage and display, industrial production, biomedicine, environmental testing and so on. The earth is driving these applications to new levels and steps.
However, the existing laser technology has always been a short board, that is, can only issue a single wavelength or narrow band of light. How to expand the frequency of the laser to form ultra-wideband, super continuous, covering ultraviolet, visible and infrared band of coherent white laser, is still a dream yet to achieve, is a worldwide problem of science and technology. This is because the laser consists of an optical resonator, a gain medium and a pump source. The wavelength of the laser is determined by the energy level structure of the atoms, molecules or ions in the gain material. Since the natural laser crystal material has a large margin in the gain frequency range and the gain bandwidth, the 5mw laser pointer can not produce any wavelength laser.
1961 invented the nonlinear frequency conversion technology (frequency, frequency, frequency difference, parameter amplification, etc.) can be a good quality laser laser light output of a fixed wavelength, through the nonlinear crystal material conversion to the difficult or fundamental It is impossible to directly obtain the wavelength range, therefore, the nonlinear frequency conversion technology is to broaden the laser output wavelength of the important means, and non-linear crystal material is the basis of the technology. Nonlinear frequency conversion requires phase matching, in the phase matching conditions, the nonlinear process can get the maximum conversion efficiency. Birefringence matching and quasi-phase matching are two commonly used phase matching techniques, suitable for different green laser pointer systems.
However, due to the dispersion effect of all the nonlinear crystals at present, the phase matching in the nonlinear process can not be automatically satisfied. Under the birefringence matching and quasi-phase matching technique, the frequency conversion range and bandwidth of the nonlinear crystal material still exist Big limitation. In fact, the laser system currently produced by the laser system is far from covering all the bands, many important wavelengths and no corresponding lasers. In addition, the bandwidth of the laser is limited, the best titanium sapphire femtosecond laser can only cover the range of 300nm, and its central wavelength at 800nm. Since laser inventions and nonlinear optics have been born for 50 years, no program can produce true white lasers.