Friends who have seen science fiction films must not forget the laser weapons in Star Wars! The Jedi Knights armed with a light sword and a wave of power, any hard metal will be interrupted. In the film Resident Evil, the network of laser beams came to the special forces, I saw a person who was instantly cut into pieces. Row, it sounds a bit disgusting, what is laser? Is the laser really so amazing?
Form a "laser" and complete two important steps first
"Laser" is the abbreviation of "Light Amplification by Stimulated Emission of Radiation", which means "using excitation radiation to increase the intensity of light". The so-called "excitation radiation" is actually completing two important steps, the first one. It is "Pumping" and the second is "Resonance":
Energy stimulation (Pumping)
Solid-state lasers (mostly using photoexcited light) belong to "atomic luminescence". The principle of atomic luminescence has been introduced earlier. The applied energy (light energy or electric energy) excites the atoms of the doping atoms from the inner level to the outer level. When the electrons jump back to the inner energy level from the outer energy level, the energy is released in the form of light energy, as shown in Figure 2(a). Semiconductor lasers (mostly using electro-excitation light) are "semiconductor luminescence". The principle of semiconductor luminescence has been introduced in the past: the application of energy (light energy or electric energy) to excite the semiconductor electrons from the valence band to the conduction band, when the electrons are When the conduction band jumps back to the valence band, the energy is released in the form of light energy, as shown in Figure 2(b).
In order to emit laser light, stimulated radiation is the most basic condition. As shown in Figure 2(c), energy excitation has two modes: "light-excited light (PL)" or "electrically-excited light (EL)", regardless of which one is used. All kinds of methods can produce laser light. Photoexcitation light (PL) is applied light to make electrons jump. Electroluminescence (EL) is applied energy to make electrons jump, which will be described in detail later.
Figure 2 Principle of energy excitation
Resonance amplification
Add a pair of "cavity" to the illuminating area. The resonant cavity can actually be composed of a pair of mirrors. As shown in Figure 3, the beam is reflected back and forth between the left and right mirrors, and the light is continuously absorbed through the illuminating area. Yes, the resonance effect is finally generated, and the energy of the light is amplified.
Photoluminescence (PL: Photoluminescence)? We use Ti Sapphire laser as an example. Firstly, titanium sapphire crystal is obtained by doping titanium atoms into sapphire, and many high-brightness light sources are placed around the crystal. The wavelength of light is directed at the crystal. When the crystal absorbs light energy to produce "energy pumping," another wavelength (color) of light is emitted. The emitted light is reflected back and forth by the two mirrors on the left and right to produce "Resonance". Since the mirror on the right can penetrate 5% of the light, the high-energy laser will be transmitted through the right side. As shown in Figure 3 (a).
Electroluminescence (EL: Electroluminescence) We take "GaAs laser diode" as an example. First, each layer of metal electrode is vapor-deposited on the gallium arsenide laser diode chip (about one grain of sand). Applying a voltage to the chip, when the chip absorbs electrical energy to produce "energy pumping," it emits light of a certain wavelength (color). The emitted light is reflected back and forth by the left and right crystal mirrors to produce "Resonance". Since the mirror on the right can penetrate 5% of the light, the high-energy laser beam will be worn by the right. Transmitted, as shown in Figure 3 (b).
Figure 3 Principle of laser generation
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