Introduction to Gas Lasers

The most common ones are helium-neon lasers, argon ion lasers, carbon dioxide lasers, helium-cadmium lasers, and copper vapor lasers.

This is a type of laser that uses gas as the working medium. The gas mentioned here can be pure gas or mixed gas; it can be atomic gas or molecular gas; it can also be ion gas, metal vapor, etc. Most of them are pumped by high-voltage discharge.

Helium-neon laser is one of the earliest and most common gas lasers. It was invented in 1961 by Dr. Javan, an Iranian scholar working at Bell Labs in the United States, and his colleagues. The working substance is a mixture of helium and neon gases in a certain proportion. Depending on the working conditions, it can output lasers of 5 different wavelengths, and the most commonly used is red light with a wavelength of 632.8 nanometers. The output power is between 0.5 and 100 milliwatts, with very good beam quality. Helium-neon laser is one of the most widely used lasers currently, and can be used in surgical medicine, laser cosmetology, architectural measurement, alignment indication, phototypesetting, laser gyroscopes, etc. Many middle school laboratories are also using it for demonstration experiments.

The carbon dioxide laser, invented by Patel three years later than the helium-neon laser, is a gas laser with high energy conversion efficiency and the strongest output. At present, the quasi-continuous output has been reported to be 400 kilowatts, and the energy of microsecond pulses reaches 10 kilojoules. With proper focusing, it can produce a power density of 1013 watts/m2. These characteristics make carbon dioxide lasers widely used in many fields. In industry, it is used for processing a variety of materials, including drilling, cutting, welding, annealing, fusion, modification, coating, etc.; in medicine, it is used for various surgical operations; in the military, it is used for laser ranging, laser radar, and even directed energy weapons.

In the same year as the invention of the carbon dioxide laser, several inert gas ion lasers were invented, the most common of which is the argon ion laser. It uses ionized argon as the working substance, and most devices work in a continuous mode, but there are also a small number of pulsed operations. The argon ion laser can have more than 35 spectral lines, of which 25 are visible light with a wavelength in the range of 408.9 to 686.1 nanometers, and more than 10 are ultraviolet radiation in the range of 275 to 363.8 nanometers. The two spectral lines of 488.0 nanometers and 514.5 nanometers are the strongest, and the continuous output power can reach 100 watts. The main application areas of argon ion lasers include eye disease treatment, blood cell counting, lithography, and as a pump source for dye lasers.

The helium-cadmium laser invented in 1968 uses cadmium metal vapor as the luminescent material. It mainly has two continuous spectral lines, namely ultraviolet radiation with a wavelength of 325.0 nanometers and blue light with a wavelength of 441.6 nanometers. The typical output power is 1 to 25 milliwatts and 1 to 100 milliwatts respectively. The main application areas include movable type printing, blood cell counting, integrated circuit chip inspection and laser induced fluorescence experiments.

Another common metal vapor laser is the copper vapor laser invented in 1966. It is generally excited by electron collisions. The two main working spectral lines are green light with a wavelength of 510.5 nanometers and yellow light with a wavelength of 578.2 nanometers. The typical pulse width is 10 to 50 nanoseconds, and the repetition frequency can reach 100 kHz. At the current level, the energy of a pulse is about 1 millijoule. That is to say, the average power can reach 100 watts, and the peak power is as high as 100 kilowatts.

It took 15 years for the copper vapor laser to enter the commercialization stage after its invention. Its main application field is the pump source of dye laser. In addition, it can also be used for high-speed flash photography, large-screen projection television and material processing.