Lasers are devices that use the principle of stimulated radiation to amplify or oscillate light in some excited substances.
The matter is excited by light, electricity and other methods, so that some of the particles are excited to a higher energy state. When the number of particles in this state is greater than the number of particles in the lower energy state, the matter can be affected by stimulated radiation. The optical radiation of a certain wavelength produces amplification, that is, when the optical radiation of this wavelength passes through the material, it emits optical radiation whose intensity is amplified and is consistent with the wave position, frequency and direction of the incident light. This is called a laser amplifier.
If the excited substance is placed in the resonant cavity, the light radiation reflects back and forth along the axis in the resonant cavity, and passes through the substance many times, and the light radiation is amplified many times to form a beam "laser" with high intensity and concentrated direction. This is the laser oscillator.
Working principle: The CO2 molecule is a linear symmetrical molecule. Two oxygen atoms are on both sides of the carbon atom, which represents the equilibrium position of the atoms. The atoms in the molecule are always in motion, and constantly vibrate around their equilibrium position. According to the molecular vibration theory, CO2 has three different vibration modes: ① The two oxygen atoms vibrate in opposite directions along the molecular axis, that is, the two oxygens reach the maximum value and equilibrium value of vibration at the same time during the vibration, and the The carbon atom is stationary, so its vibration is called symmetrical vibration. ② The two oxygen atoms vibrate in the direction perpendicular to the molecular axis, and the vibration direction is the same, while the carbon atom vibrates in the opposite direction and perpendicular to the molecular axis. Since the vibrations of the three atoms are synchronized, it is also called deformation vibration. ③The three atoms vibrate along the axis of symmetry, and the vibration direction of the carbon atom is opposite to that of the two oxygen atoms, which is also called antisymmetric vibrational energy. In these three different vibration modes, it is determined that there are different groups of energy levels.
CO2 laser tube: It is the most critical part of the laser machine. It is usually made of hard glass and generally adopts a layered sleeve structure. The innermost layer is the discharge tube, the second layer is the water-cooled casing, and the outermost layer is the gas storage tube. The diameter of the discharge tube of the carbon dioxide laser is larger than that of the He-Ne laser tube. Generally speaking, the thickness of the discharge tube has no effect on the output power, mainly considering the diffraction effect caused by the size of the spot, which should be determined according to the tube length. The longer tube is thicker, and the shorter tube is thinner. The length of the discharge tube is proportional to the output power. Within a certain length range, the output power per meter of discharge tube length increases with the total length. The purpose of adding a water cooling jacket is to cool the working gas and stabilize the output power. The discharge tube is connected to the gas storage tube at both ends, that is, one end of the gas storage tube is connected with the discharge tube with a small hole, and the other end is connected with the discharge tube through the spiral return tube, so that the gas can circulate in the discharge tube and the gas storage tube Flow, the gas in the discharge tube is exchanged at any time.
Optical resonant cavity: The resonant cavity of CO2 laser is usually flat and concave. The mirror is made of K8 optical glass or optical quartz, which is processed into a concave mirror with a large radius of curvature. The mirror surface is coated with a metal film with a high reflectivity—a gold-plated film. The reflectivity at the wavelength of 10.6μm reaches 98.8%, and the chemical properties are stable. The light emitted by carbon dioxide is infrared light. Therefore, the reflector needs to use materials that transmit infrared light, because ordinary optical glass is not transparent to infrared light. It is required to make a small hole in the center of the total reflection mirror. Then seal a piece of infrared material that can transmit 10.6μm laser to seal the gas. This makes a part of the laser in the resonant cavity output from this small hole to form a laser beam.
Power supply and pump: The discharge current of the enclosed CO2 laser is relatively small. It uses cold electrodes and the cathode is made of molybdenum or nickel plates into a cylindrical shape. With a working current of 30-40mA, the area of the cathode cylinder is 500cm2, so that the lens will not be polluted. A light barrier is added between the cathode and the lens. The pump is excited by a continuous DC power supply. The principle of the DC power supply for exciting the CO2 laser is that the DC voltage is to increase the AC voltage in the city with a transformer, and obtain high-voltage electricity through high-voltage rectification and high-voltage filtering to add to the laser tube.