الخميس، تشرين الثاني ٢٧، ٢٠٠٨

Excimerlaser
  • RD-EXC-5
  • RD-EXC-20
  • RD-EXC-200
  • RD-EXC-300
Our Excimer laser are small sized and low priced standard laser with metal oxide ceramic discharge chamber, integrated power supply and corona pre-ionization. Solid nickel electrodes are used near the gas discharge where the halogens are most reactive. This provides a longer component lifetime and a better long-term beam uniformity. The laser are equipped with an internal electrostatic window protection system to increase the gas lifetime and the window cleaning intervals.
In combination with our dye lasers this laser opens a variety of applications in the field of spectroscopy and non-linear optics where medium pulse energies and powers at repetition rates of up to 200 Hz are needed.
http://www.youtube.com/watch?v=frqv-j6agkU

Types of Modern Excimer Lasers Used for LASIK

Slit scanning lasers — Slit scanning lasers use relatively small beams linked to a rotational device with slit holes that enlarge. The laser beams scan across these holes during surgery, producing a gradually enlarging ablation zone. The approach provides a uniform beam and — potentially — smoother ablations than obsolete broad-beam lasers. The disadvantages include a slightly greater risk of decentration and overcorrection unless an eye-tracker is being used with the laser.

Spot scanning lasers — Spot scanning (or "flying-spot") lasers, which are the most common, use small-diameter laser beams (0.8 to 2 mm) scanned across the cornea to produce the ablation zone. This approach has the potential to produce the smoothest ablations, to more readily allow customized ablations and to better treat irregular astigmatism.

Wavefront-guided lasers — Many excimer lasers are connected to a device that detects and "maps" defects in the eye's optical system, based on how lightwaves travel through the eye. These wavefront devices individually guide the way the eye's cornea is reshaped to achieve a custom LASIK ablation. Both slit scanning and spot scanning lasers have the ability to be used for wavefront-guided treatments.

Excimer Lasers and Eye Tracking

Most modern excimer lasers have automated eye tracking systems to keep the laser beam on target. Studies have shown that eye trackers produce better outcomes and decrease LASIK complications compared with past lasers that did not use eye tracking systems.

Indications and Features of Excimer Lasers

In the following chart, OZ stands for optical zone, meaning the maximum size of the pupil allowing light to pass through the eye that can be targeted effectively for correction with a specific laser. TZ stands for the maximum treatment area, including a transition zone that can be used in an ablation to achieve vision correction in the targeted area.

Applications

The short wavelengths in the ultraviolet spectral region make possible a number of applications:

  • the generation of very fine patterns with photolithographic methods, e.g. in semiconductor chip production
  • material processing with laser ablation, exploiting the very short absorption lengths of the order of a few micrometers in many materials, so that a moderate pulse fluence of a few joules per square centimeter is sufficient for ablation
  • pulsed laser deposition
  • laser marking and microstructuring of glasses and plastics
  • fabrication of fiber Bragg gratings
  • ophthalmology (eye surgery), particularly for vision correction with ArF lasers at 193 nm; common methods are laser in-situ keratomileusis (LASIK) and photorefractive keratectomy (PRK)
  • psoriasis treatment with XeCl lasers at 308 nm
  • pumping other lasers, e.g. certain dye lasers

Note that excimer lasers raise a variety of safety issues, related to the use of high voltages, the handling of poisonous gases (halogens), and the risk of causing skin cancer and eye damage by irradiation with ultraviolet light.

types of excimer lasers

Different types of excimer lasers typically emit at wavelengths between 157 and 351 nm:

ExcimerWavelength
F2 (fluorine)157 nm
ArF (argon fluoride)193 nm
KrF (krypton fluoride)248 nm
XeBr (xenon bromide)282 nm
XeCl (xenon chloride)308 nm
XeF (xenon fluoride)351 nm

Typical excimer lasers emit pulses with a repetition rate up to a few kilohertz and average output powers between a few watts and hundreds of watts, which makes them the most powerful laser sources in the ultraviolet region, particularly for wavelengths below 300 nm. The power efficiency varies between 0.2 and 2%.

Excimer Lasers

An excimer laser is a powerful kind of laser which is nearly always operated in the ultraviolet (UV) spectral region (→ ultraviolet lasers) and generates nanosecond pulses. The excimer gain medium is a gas mixture, typically containing a noble gas (rare gas) (e.g. argon, krypton, or xenon) and a halogen (e.g. fluorine or chlorine, e.g. as HCl), apart from helium and/or neon as buffer gas. An excimer gain medium is pumped with short (nanosecond) current pulses in a high-voltage electric discharge (or sometimes with an electron beam), which create so-called excimers (excited dimers) – molecules which represent a bound state of their constituents only in the excited electronic state, but not in the electronic ground state. (More precisely, a dimer is a molecule consisting of two equal atoms, but the term excimer is normally understood to include asymmetric molecules such as XeCl as well. The term rare gas halide lasers would actually be more appropriate, and the term exciplex laser is sometimes used.) After stimulated or spontaneous emission, the excimer rapidly dissociates, so that reabsorption of the generated radiation is avoided. This makes it possible to achieve a fairly high gain even for a moderate concentration of excimers