The results of the experimental investigations of the discharge-pumped KrCl (223 nm) excimer laser with the TPI thyratron
(pseudo spark gap) as a high-voltage switch are presented. The experimental investigation of the energy and temporal
parameters of the pumping and radiation for KrCl laser on the Ne:Kr:HCl mixture with an excitation system of the LC-inverter
type based on TPI 10k/20 thyratron was carried out. The comparative analysis of the laser pumping and radiation
parameters with those obtained for excitation system based on a spark gap RU-65 as a high-voltage switch was performed.
As a result the output radiation energy for a laser with thyratron TPI 10k/20 was obtained to be of 40% higher than that with
spark gap RU-65 at the same pumping conditions. The higher output energy and efficiency of the TPI based laser was
considered to be due to higher efficiency of energy transfer from storage to discharge circuit and to active media owing to
lower energy losses into TPI thyratron in comparison with the RU-65 spark gap. For KrCl excimer laser in Ne:Kr:HCl
mixture the total efficiency of 1.5% with output energy of 0.65 J was obtained for the first time.
The experimental investigations results of spectral, energy and temporal parameters of the first inductive N2, FI and CO2 gas lasers are reported. The excitation system for formation of the achievement the pulsed cylindrical inductive discharge in gas mixtures is described. For the first time the nitrogen inductive laser (337.1 nm) with pulse power of 350 kW was created. The generation energy of 4.6 mJ with the pulse duration (FWHM) of 12±1 ns was achieved. The total efficiency of nitrogen inductive laser was 0.05 %. The laser beam has a ring form with an outer diameter of 43 mm, thickness of
1.5-2.0 mm and the divergence of 0.3 mrad. For FI inductive laser the lasing was observed on 8 lines (623-755 nm). The
maximal output energy of 2.6 mJ was achieved in He:F2-100:1 gas mixture. The pulse duration was 80±1 ns (FWHM)
that correspond to pulse power of 32 kW. The total efficiency of the FI inductive laser was 0.01 %. The ring laser beam
has an outer diameter of 43 mm, thickness of 3.0 mm and the divergence of 0.4 mrad. For CO2 (10.6 um) inductive laser
the maximal output energy of 150 mJ was achieved in gas mixture He:N2:CO2 - 8:1:1. The pulse duration (FWHM) was
170 us that corresponds to a pulse power of 0.9 kW. The laser beam has a ring form with dimension of an outer diameter
of 33 mm with the thickness about 6.0-6.5 mm and the divergence of 4.0 mrad.
The results of using the thyratron of the TPI series (pseudo spark gap) as a high-voltage switch in the excitation system of
ArF (193 nm) excimer laser are presented. The excitation system of the LC-inverter type based on TPI 10k/20 thyratron in
absence of any non-linear elements was developed. An experimental investigation of the energy and temporal parameters of
the pumping and lasing for ArF laser on the He:Ar:F2 mixture with excitation system developed was carried out. The
comparative analysis of the ArF laser pumping and radiation parameters in dependence of the high-voltage switch type such
as a standard spark gap RU-65, and thyratron TPI 10k/20 was performed. The output radiation energy for a laser with
thyratron TPI 10k/20 was obtained to be of 1.4 times higher than that with standard spark gap RU-65 at the same pumping
conditions. Such increase the output energy was shown to be achieving owing to higher level of the pumping intensity due
to higher voltage on the discharge gap that occurs due to lower energy losses into TPI thyratron in comparison with the RU-
65 spark gap and leads to more efficient energy transfer from storage to discharge circuit. As a result for ArF laser with TPI
thyratron in He:Ar:F2 mixture the output radiation energy of 1.0 J with the total efficiency of 1.7% has been achieved. The
advantages of using the TPI thyratron in the excitation system of the ArF excimer laser over spark gap are described.
The results of first inductive gas lasers creation in UV, VIS and IR ranges of spectrum are reported. A pulsed cylindrical inductive discharge was used to population inversion formation on the transitions of atoms and molecules. The excitation system producing an inductive discharge in gases under a pressure within a range from 0,1 to 1,0 atm has been developed. Lasing on the transitions of nitrogen molecules (337,1 nm), fluorine atoms (623-755 nm) and carbon dioxide molecules (10,6 um) was achieved. The results of the experimental study of spectral, temporal, and energy parameters of these inductive lasers are presented.
A pulsed transverse inductive discharge (PTID) is used to population inversion formation on the transitions in atoms and
molecules. Excitation system producing an inductive discharge in gases under a pressure within a range from 0,1 to 1,0
atm has been created. The experimental study of spectral and temporal parameters of stimulated emission for active
media on the Ne (585.3 nm), He (587.5, 667.8 nm), Ar (750.4nm) atoms and XeF* (353 nm), XeCl *(308 nm) and KrF*
(248 nm), molecules excited by an inductive transverse discharge was performed. Lasing on the transitions of fluorine
atoms and nitrogen molecules are reported. The results of the experimental study of spectral, temporal, and energy
parameters of fluorine (FI) and nitrogen inductive lasers are presented.
The results of experimental study of the pump intensity and active media parameters effect on the output energy and total efficiency of a discharge-pumped KrCl (223 nm) excimer laser on a mixture of Ne:Kr:HCl are presented. It was experimentally shown that for the achievement of maximal efficiency of a KrCl excimer laser it is necessary to use optimal pump intensity. The value of the optimal pump intensity for the laser on the mixture Ne:Kr:HC1 was found to be
in the range of 5.0-5.5 MW/cm3. To achieve such pump intensity the excitation scheme of the LC-inverter type has been used where the energy losses inside discharge circuit had been decreased. Using the pump intensity of 5.5 MW/cm3 the
output energy of 700 mJ with the total efficiency of 1.0 % was obtained for the first time.
The use of the pulsed inductive transverse discharge for an excitation of the gas lasers on the electronic transition of the
atoms and molecules was suggested. The excitation system and the discharge tube have been created to achieve the inductive transverse discharge. The inductive transverse discharge emission of rare gases and their mixtures with halogens in pressure range 1 - 450 tons was investigated. The generation on the electronic transitions of atoms Fl (703.75, 712.79 and 731.1 nm), Hel (587.5 and 667.8 nm), Nel (585.3 nm), An (750.4 nm) and excimer molecules of XeCl (308 nm), XeF (353 nm) and KrF (248 nm) have been obtained for the first time. The results of the experimental study of spectral, temporal and energetic parameters of inductive lasers developed are presented.
The results of experimental study of the pump intensity and active media parameters effect on output energy and efficiency of a discharge-pumped ArF (193 nm) excimer laser on a mixture of He:Ar:F2 are presented. It was experimentally shown that for the achievement of maximal output energy with maximal efficiency of an ArF excimer laser it is necessary to use an optimal pump intensity of 4.5-5.0 MW/cm3. To achieve such active media pump intensity the excitation scheme of the LC-inverter type has been used where the energy losses inside discharge circuit had been decreased. Using the pump intensity of 5.0 MW/cm3 in an active media of He:Ar:F2 - 79.7:20:0.3 at total pressure of 2.4 atm the output energy of 1.3 J at the total efficiency of 2.0% was obtained for the first time.
The results of experimental investigations of the pumping conditions and radiation parameters of the KrF excimer laser for achieving the output radiation energy up to 1,0 J with maximal efficiency are presented. The high voltage excitation circuit on the basis of a LC-inverter type circuit including the peaking capacitors and automatic UV preionisation (API) has been developed. For the KrF laser with the active volume of 175 cm3 in He:Kr:F2 -89,8:10:0,2% gas mixture at the total pressure of 2,7 atm the overall efficiency up to 2,2% with the output radiation energy of 0,84 J was achieved. The maximum output energy of the KrF laser was of 1,0 J with the overall efficiency of 2,0%. The pulse duration (FWHM) was 24±1 ns. The addition of up to 50% of Ne as a buffer gas to He at the pressure of 2,9 atm increases the maximal output energy up to 1,3 J with efficiency of 2,5% and the maximal efficiency up to 2,9% with output energy of 0,95 J.
KEYWORDS: Crystals, Diffraction gratings, Diffraction, Refractive index, Waveguides, Laser crystals, Photorefraction, Absorption, High power lasers, Chemical species
A phenomenon of a strong irreversible variation of the refractive index (Δn approximately equals - 0.2) in a subsurface layer of the lithium niobate crystal has been observed. The effect arises under the strong absorption of high-power radiation with wavelength 248 nm of KrF excimer laser. The characteristics of the subsurface photorefractive effect (SPRE) were identified by using the data on measurements of the reflection coefficient of a crystal and of the diffraction efficiency of a recorded phase grating. About 40% of niobium and oxygen atoms has been found to be displaced from the lattice points in the 350 ± 50 angstrom subsurface layer. This phenomenon was used for creation of some integrated optics elements.
In present paper the findings on chromosome mutations, the nature of damage and the repair of the cornea tissue after UV irradiation by excimer lasers at 193, 223 and 248 nm were made. Structural mutations induced by short-pulses UV irradiation were shown to be similar to spontaneous ones by the type, time of formation in the mitotic cycle and location of acentrics. Ten hours after irradiation of the cornea with doses of 0,09 to 1,5 J/cm2 the incidence of cells with chromosome aberrations increased linearly with dose and amounted to 11,7% at 248 nm, 5,5% at 223 nm and 2,6% at 193 nm per 1 J/cm2. No induced chromosome aberrations occurred 72 hour following irradiation. Within the dose range from 3,0 to 18 J/cm2 the cytogenesis effect of radiation was less manifest than that with the doses mentioned above, the frequency of chromosome aberrations being independent of either radiation wavelength or radiation dose and amounted of 2,5 to 3,0%. Thus, large doses of powerful short-pulse UV radiation are safe according to the structural mutation criterion.
The results experimental investigations of an interaction of the UV laser radiation with human eye cornea are described. In experiments the ArF (193-nm), KrCl (223-nm), KrF (248-nm) excimer lasers were used. The transmission spectra in UV region, the ablation rate and traumatic effects of different wavelengths to the human eye cornea were studied in detail. The biological safety of using the short-pulsed UV radiation from the point of view of chromosome rearrangement in the cells of eye has been shown. The UV ophthalmic laser systems based on the ArF (193-nm) and the KrCl (223-nm) excimer lasers were created and comparative analysis of using ones in ophthalmology was performed. The system with the radiation wavelength of 223-nm of the KrCl excimer laser for refractive surgery was shown to have several medical and technical advantages over the system with the traditionally used radiation wavelength of 193-nm of the ArF excimer laser. In addition the use of the wavelength of 223-nm extends functional features of the system, allowing to make not only correction of refractive errors and therapeutic procedures but also to treat such ocular diseases as the herpes simplex virus. For the first time the application of UV excimer lasers (193, 223 and 248-nm) for herpetic keratitis treatment was investigated. The advantages and disadvantages of using each radiation wavelengths for healing efficiency of simplex herpes virus were demonstrated. Optimal laser radiation parameters for the treatment of the herpetic keratitis were determined. The results of clinical trials are presented.
For the first time the effect of the UV laser radiation to human eye cornea with herpetic keratitis was experimentally investigated. In experiments the UV radiation of ArF (193 nm), KrCl (223 nm), KrF (248 nm) excimer lasers were used. Optimal laser radiation parameters for the treatment of the herpetic keratitis were determined. The immuno-biochemical investigations were carried out and the results of clinical trials are presented. The maximum ablation rate was obtained for the 248 nm radiation wavelength. The process of healing was successful but in some cases the haze on the surface of the cornea was observed. When used the 193 nm radiation wavelength the corneal surface was clear without any hazes but the epithelization process was slower than for 248 nm wavelength and in some cases the relapse was occurred. The best results for herpetic keratitis treatment have been achieved by utilizing the 223 nm radiation wavelength of the KrCl excimer laser. The use of the 223 nm radiation wavelength allows treating the herpetic keratitis with low traumatic process of ablation and provides high quality of corneal surface.
The excimer laser ophthalmic system Medilex including the ArF (193-nm) excimer laser with optical delivery system and optical coherence tomograph (OCT) for correction of the refraction anomalies is presented. The new optical system has been developed. The possibility of the controlling the corneal surface with micron accuracy by OCT apparatus during the process of UV laser ablation is shown. OCT device is able to measure surface profile, thickness of the cornea and depth of removed tissue during process of UV ablation. Preliminary results on the determination of the surface profile and thickness of the non-modified by UV laser cornea of the alive human eye performed by OCT device with accuracy about 5 micrometers is shown. The results of the experiments on the measurement of the removed material depth on polymer film and cadaverous human eyes simultaneously with ablation process are described.
The new surgical UV ophthalmic laser system Medilex based on the KrCl (223 nm) excimer laser for refractive surgery was created. The comparative analysis of using the UV ophthalmic laser systems Medilex based on the ArF (193 nm) and the KrCl (223 nm) excimer lasers for the correction of refractive errors was performed. The system with the radiation wavelength of 223 nanometer of the KrCl excimer laser for refractive surgery was shown to have several medical and technical advantages over the system with the traditionally used radiation wavelength of 193 nanometer of the ArF excimer laser. In addition the use of the wavelength of 223 nanometer extends functional features of the system, allowing to make not only standard for this type systems surgical and therapeutic procedures but also to treat such ocular diseases as the glaucoma and herpetic keratities. For the UV ophthalmic laser systems Medilex three variations of the beam delivery system including special rotating masks and different beam homogenize systems were developed. All created beam delivery systems are able to make the correction of myopia, hyperopia, astigmatism and myopic or hyperopic astigmatism and may be used for therapeutic procedures. The results of the initial treatments of refractive error corrections using the UV ophthalmic laser systems Medilex for both photorefractive keratectomy (PRK) and LASIK procedures are presented.
The using of KrCl (223 nm) excimer laser in ophthalmic devices for Photorefractive Keratectomy (PRK) and phototherapeutic Keratectomy (PTK) is offered. The structure and functions of a new surgical UV ophthalmic laser systems Medilex using ArF (193 nm) or KrCl (223 nm) excimer laser for corneal surgery are presented. The systems Medilex with the new optical delivery system is used for photoablative reprofiling of the cornea to correct refraction errors (myopia, hyperopia and astigmatism) and to treat a corneal pathologies. The use of the 223 nanometer laser is proposed to have advantages over the 193 nanometer laser. The results of application of the ophthalmic excimer laser systems Medilex for treatment of myopia are presented.
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