As the short cavity semiconductor lasers, laser direction is poor, especially in the end of the vertical plane, a large divergence angle, up to 2030. In the end of the horizontal plane, the divergence angle of about several times. Figure (5-30) gives the spatial distribution of the semiconductor laser beam diagram. Figure (5-31) is a GaAs laser emission spectra. One figure (a) is below the threshold of the fluorescence spectrum, spectral width is generally a few hundred angstroms, Figure (b) is the injection current to or greater than the threshold value of laser spectroscopy, tens of angstroms wide spectrum. Although the semiconductor laser spectral width is much narrower than the fluorescence, but lower than the gas and solid-state lasers to be much wider. With the emergence of new devices, spectral width has been improved, such as distributed feedback laser linewidth, and only about 1 angstrom. More processing machine of green laser pointer can ensure the high output of green laser pointer .
Where, V is the voltage drop on the pn junction, RS is the laser series resistance (including resistivity and contact resistance). As the laser operating current greater resistance power-hungry, so the power efficiency at room temperature only a few percent. By different p-type semiconductor material and n-type semiconductor pn junction formed called heterojunction. To overcome the shortcomings of homojunction semiconductor lasers, to improve power and efficiency, reduce the threshold current, developed a heterojunction semiconductor lasers. Single-heterojunction device structure shown in Figure (5-32) (b) below, by a single heterojunction p-GaAs and p-GaAlAs formed. Electrons from the n region into the p-GaAs, heterojunction because of the high barrier limit, the active region thickness d2. Only the complete and signed material inquisition sheet of green laser pointer can get the material the workshop needs from the warehouse of green laser pointer .
Also, because p-GaAlAs refractive index is small, "waveguide effect" is significant, the light transmission limits in the active zone. These two factors make single-heterostructure laser threshold current density is reduced 1 ? 2 orders of magnitude, about 8000A/cm2. Double-heterostructure semiconductor laser refers to the active area on both sides, there are two heterojunction, as shown in Figure (5-32) (c) below. Double-heterostructure laser active region injected electrons and holes, due to both sides of the high barrier limit, depth surge, the thickness of the active region narrows, d0.5. Meanwhile, both sides of the active region refractive index difference is enormous, "waveguide effect" is very significant, so that light transmission loss greatly reduced. Therefore, the double-heterostructure laser threshold current density lower, can be reduced to 102 ? 103A/cm2. Room temperature, availability of a few milliwatts to several hundred milliwatts of continuous power output. The drawing of green laser pointer should be maintained in the good status.
The above described solid, gas, semiconductor, and dye lasers, which are some of the older and more mature and developed the laser. Furthermore, there are excimer lasers, free electron lasers, chemical lasers, fiber lasers and some newly developed and there is a better prospect of laser devices. This section briefly describes these lasers. Under normal atom, the excited state can be temporarily combined into unstable molecules, called excimer, referred to as the excimer. Excimer laser is the excimer gas working substance. Since 1970, the first since the advent of excimer lasers, it successfully developed a variety of excimer lasers, and isotope separation, photochemistry, pumped dye lasers has made a contribution. Some parameters in the drawing of green laser pointer should be revised.
Laser weapons development in the area, it is also one of very promising laser. Excimer laser treatment of myopia has also achieved good economic and social benefits. So far, excimer lasers are more and more incentives also continue to improve, increasing power and efficiency. Joule energy pulse output has reached one hundred orders of magnitude, the pulse peak power of kilowatts or more, repetition rate of 200 times / sec, the beam divergence angle 0.15mrad. Excimer laser is characterized as follows: level structure has distinctive features. Figure (5-33) shows, A indicates a higher excited state, B the laser upper level, C, said the ground state. Most items of green laser pointer agreement has been determined.
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