What Is an Excimer Laser?

Excimer laser, a type of gas laser device using excimer as the working substance. Relativistic electron beams (energy greater than 200 kilo-electron volts) or lateral rapid pulse discharges are commonly used to achieve excitation. When an unstable molecular bond of an excited excimer breaks and dissociates into ground state atoms, the excited state energy is emitted in the form of laser radiation.

The first excimer laser was born in 1970. It used a strong electron beam to excite liquid xenon to obtain the lasing effect of xenon excimer. The laser wavelength was 1720 angstroms. Subsequently, gaseous xenon molecules and other rare gas excimers, rare gas oxide excimers (krypton oxide, xenon oxide, argon oxide, etc.), metal vapors-rare gas excimers (sodium xenon oxide, etc.); rare gas monohalide excimers Molecules (xenon fluoride, argon fluoride, krypton fluoride, xenon chloride, xenon bromide, xenon iodide, krypton chloride, etc.), metal halide excimers (mercury chloride, mercury bromide, etc.) and metal Molecules (sodium excimer, etc.) are born one after another. The excimer laser material has a low energy state repulsion and can be effectively evacuated, so there is no low state absorption and energy loss. The number of particles is easily reversed, the gain is large, the conversion efficiency is high, the repetition rate is high, and the radiation wavelength is short. It oscillates in the ultraviolet and vacuum ultraviolet (a few extend to visible light), with a wide tuning range. It is used in the separation of isotopes, ultraviolet photochemistry, laser spectroscopy, rapid photography, high-resolution holography, laser weapons, material structure research, optical communications, remote sensing, integrated optics, nonlinear optics, agriculture, medicine, biology, and pumping. Tuning dye lasers have been widely used, and they are expected to develop into laser devices for nuclear fusion.

1. An excimer exists in an excited state with a short lifetime, only 10 ^ (-8) S, and the ground state is 10 ^ (-13) S. The transition occurs in a low-excited state and a repelled ground state (or Weak binding), the fluorescence spectrum is a continuous band.

2. Because its fluorescence spectrum is a continuous band, wavelength tunable operation can be achieved.

3. Due to the rapid dissociation of ions at the lower level (ground state) of the laser transition, the lower level of the laser is basically empty, and the number of particles is easily reversed. Therefore, the quantum efficiency is very high, close to 100%, and it can operate at high repetition frequencies. .

4. The output laser wavelength is mainly in the ultraviolet to visible light range. The wavelength is short, the frequency is high, the energy is large, the focal spot is small, and the processing resolution is high. It is more suitable for high-quality laser processing. ^[1]

There are many types of lasers used in the medical field.Rudy lasers, argon ion (Ar +) lasers, krypton ion (Kr +), dye (dye) lasers, and neodymium-doped yttrium aluminum garnet ( (Nd: YAG) laser and argon fluoride (ArF) excimer laser such as solid, gas and liquid lasers, using continuous, pulsed and Q-switched methods to treat the number of pigmentary membranes and refractive interstitial sites at the bottom of the eye Ten related eye diseases.

The excimer laser used in ophthalmology is a laser generated by using Argon and Fluoride as working gases. The so-called excimer laser refers to the laser light generated by the stimulated dimer (inert gas and halogen element), which has a wavelength range of 157 to 353 nm and belongs to the ultraviolet laser band. A argon fluoride (ArF) mixture for clinical use generates an ultra-ultraviolet cold laser with a wavelength of 193nm.

ArF excimer laser with a wavelength of 193nm, the mechanism of refractive surgery is photochemical effect. The energy of a single photon of an excimer laser is approximately 6.4 eV, while the binding energy of a peptide bond and a carbon molecular bond in the corneal tissue is only 3.6 eV. When its high-energy photons are irradiated to the cornea, the molecular bonds in the tissue are directly broken, leading to the fragmentation of the corneal tissue and the purpose of ablating and cutting the tissue, and because the excimer laser pulse width is short (10-20nm), it is also photochemical Effect resection. Therefore, the mechanical and thermal damage to the surrounding tissue is minimal ( 0.30 m).

Using this knife to perform phototomy, the cutting accuracy can reach m level, and the damage range of the blade edge is only nm level, and it does not damage adjacent tissues because there is no thermal effect. So it has been used in corneal surgery, such as corneal refractive surgery, corneal scar removal and so on.