XeCl excimer laser

A XeCl excimer laser , also called a 308 nm excimer laser , is an excimer laser based on xenon chloride (XeCl), the wavelength of which is 308  nm ( ultraviolet radiation ). It is mainly used for the targeted therapy of diseased skin areas with UV-sensitive skin diseases , especially psoriasis , chronic eczema ( neurodermatitis ) and vitiligo (white spot disease). At the end of the 1990s, the first publications by a Hungarian working group on excimer laser therapy for skin diseases can be found.

Physical basics

The XeCl excimer laser uses the excimer xenon chloride (XeCl) as the active medium. A mixture of 4… 5 mbar hydrogen chloride , 80 mbar xenon and 2.4 bar helium is used as the buffer gas as the gas. As with other excimer lasers, the energy to form the excimers is supplied by a short, high-current electrical discharge ( gas discharge ). The unstable molecule xenon chloride quickly breaks down into its two components xenon and chlorine . A photon with a wavelength of 308 nm is emitted. The laser gives with a repetition frequency of z. B. 200 Hz from approx. 60 ns short pulses that result in the desired energy density through time summation . Each impulse has an energy of, for example, approx. 3… 7 mJ.

See also : excimer laser

Areas of application

medicine

With a wavelength of 308 nm, the XeCl excimer laser emits in the range of the optimal antipsoriatic spectrum (300-313 nm) and is therefore used in dermatology for so-called 311 nm narrowband UVB therapy. In contrast to conventional UV therapy with lamps, the laser enables targeted irradiation of the diseased skin areas, while the unaffected skin is spared from the radiation exposure. Dermatoses can be treated with higher energy doses compared to whole-body phototherapy, whereby a reduction in the number of radiation sessions and the radiation dose is achieved at the same time .

Although no meaningful data are currently available with regard to possible long-term side effects, it can be assumed that the risk of undesirable radiation effects such as premature skin aging and the development of skin cancer can be reduced compared to whole-body radiation by protecting the unaffected skin . Targeted irradiation of only the psoriatic plaques protects healthy skin; a reduction of skin aging and photo- carcinogenesis can be expected in the long term compared to the conventional full-body phototherapy. Although individual therapy doses between 800 mJ / cm² and 2,000 mJ / cm² are applied in laser therapy, the cumulative radiation dose only reaches approx. 50% of a 311 nm narrow-spectrum therapy with total energy doses of more than 20 J / cm² due to the significantly shorter total treatment time become.

Since therapy with the 308 nm excimer laser is a further development of the UVB therapy that has been tried and tested for decades, all skin diseases that can be successfully treated with UVB light are also particularly suitable for treatment with the 308 nm excimer laser . The tissue interactions are comparable to those of narrow-spectrum therapy with 311–313 nm. With the excimer laser, however, an increased induction of T-cell apoptosis was observed, which explains the higher response rate and faster effectiveness.

Approval from the US Food and Drug Administration has existed since 2000 for the indications psoriasis, neurodermatitis and vitiligo. The 308 nm excimer laser can be used successfully for all UVB-sensitive dermatoses such as psoriasis vulgaris ( psoriasis ), psoriasis pustulosa palmoplantaris and inversa, atopic eczema (neurodermatitis), chronic hand and foot eczema, head eczema, vitiligo, hypopigmentation for striae distensae, post-traumatic , laser-induced), alopecia areata , acne , perioral dermatitis , lichen vidal , lichen planus ( lichen planus ), parapsoriasis en plaque, etc. a. For the treatment of psoriasis, therapy with the 308 nm excimer laser has been included in the S3 psoriasis guideline .

Further areas of application

XeCl excimer lasers are also used as pump lasers for dye lasers , since the wavelength of 308 nm is in the range of the absorption bands of many laser dyes, for example coumarin -307. In principle, they are also suitable as a radiation source for photolithography. Corresponding systems were not able to establish themselves in industry or in research and are of practically no importance, since when switching to shorter wavelengths (for a higher resolution) from mercury vapor lamps (348 nm) one switched directly to KrF excimer lasers (248 nm). Furthermore, commercial XeCl laser systems for other applications in the field of semiconductor and microtechnology were also occasionally presented, for example for the thermal healing of materials, laser ablation or for labeling different materials.

With its wavelength of 308 nm, the laser is suitable for stimulating acetone to fluoresce . This is used in research to carry out concentration measurements using the tracer LIF method .

literature

• H. Grema, C. Raulin: The excimer laser in dermatology and aesthetic medicine. In: Der Hautarzt 55, 2004, pp. 48–56.

Individual evidence

1. ↑ Dirk Basting, Gerd Marowsky: Excimer laser technology . Springer, 2005, ISBN 978-3-540-20056-7 , pp. 45 (fluorescence and laser spectrum, also compared to KrF and ArF excimer lasers).
2. ↑ Jürgen Eichler, Hans-Joachim Eichler: Lasers: designs, beam guidance, applications . Springer, 2010, ISBN 978-3-642-10461-9 , pp. 128 .
3. ↑ Konrad Kleinknecht: Detectors for particle radiation . Vieweg + Teubner, 2005, ISBN 978-3-8351-0058-9 , pp. 87 .
4. ↑ Dirk Basting, Gerd Marowsky: Excimer laser technology . Springer, 2005, ISBN 978-3-540-20056-7 , pp. 16 .
5. ↑ Dirk Basting, Gerd Marowsky: Excimer laser technology . Springer, 2005, ISBN 978-3-540-20056-7 , pp. 85-88, 145, 199, 322 .

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