The aim of the presented project was comparison of two Fe:ZnSe lasers based on Fe:ZnSe bulk active crystals grown by
two different methods - Bridgman and floating zone. For pumping the Q-switched Er:YAG laser generating 15 mJ and
300 ns giant pulses was used. The highest Fe:ZnSe laser generated output energy was 1.2 - 1.3 mJ for both investigated
crystals, the pulse duration was 150 - 200 ns. The Fe:ZnSe laser threshold was reached at absorbed pumping energy of
~ 1 mJ. Tuning properties using intracavity CaF2 prism were also investigated and tuning range ~ 4 - 5 μm was observed
for both crystals.
The investigation of tensile strength needed for bracket debonding was the aim of study. A diode pumped Tm: YAP
microchip laser generating a continuous 2um radiation with the maximum output power of 4W was used for debonding
purposes. The group of 60 brackets was debonded using classical and laser irradiation methods - the doze from 1W to 4
W, 60s. The tensile strength without laser irradiation was in the range from 39.6 N (full ceramic bracket group) to 63.7 N
(ceramic bracket with metal slot group). After irradiation the tensile strength was decreased from 35.1 N (full ceramic
bracket group) to 48.8 N (ceramic bracket with metal slot group). The results of our study generally agree with the
previous studies, substantiating the fact that lasers can be used effectively to thermally soften the adhesive resin for
removal of ceramic brackets. From the practical point of view is conclusion that during laser irradiation, thermal
ablation occurs and the bracket is removed from the enamel together with the rest of the adhesive resin. Laser
debonding is easier and little heat diffusion occurred.
The goal of this work was to design and investigate a gain switched, at room temperature lasing Fe:ZnSe laser. The active medium was a bulk, by Bridgman-technique grown Fe:ZnSe sample with the thickness 3.4 mm. The pumping was provided by electro-optically Q-switched Er:YAG laser with the oscillation wavelength 2.937 μm matching the local maximum of the Fe:ZnSe absorption. The Er:YAG Q-switched operation was obtained by the Brewster angle cut LiNbO3 Pockels cell placed between the rear mirror and the laser active medium. No additional intracavity polarizers were used. The maximum pumping pulse energy and length was 15 mJ, and ~300 ns, respectively. This pulse-length is close to room-temperature measured lifetime of Fe2+ ions in Fe:ZnSe crystal.
The pump radiation was directed into the Fe:ZnSe crystal which was placed inside the cavity formed by dichroic
pumping mirror (THR=92% at 2.94 μm and RHR~100% for 3.5-5.2 μm) and optimal output coupler with the reflectance ROC=90% at 4.5 μm, radius of curvature r = -200 mm. The maximum obtained output Fe:ZnSe laser energy was 1.2 mJ, the generated output pulse duration on the wavelength 4.5 μm was 65 ns (FWHM). The output pulse profile was approximately Gaussian. The crystal showed rather high uniformity of oscillation properties throughout its volume. For the case of tuning the CaF2 prism was implemented into the resonator. The tuning curve of generated Fe:ZnSe laser radiation covered the spectral range 3.9 - 4.7 μm.
The study demonstrates the possibility of using Tm:YAP laser radiation for the removing ceramic brackets. The amount
of enamel loss and residual resin on teeth has been evaluated. A diode-pumped Tm:YAP microchip laser generating at
wavelength 1.9 μm was used for the debonding process. The transmission and absorption measurement of the basic
elements - bracket, adhesive resin, and enamel was analyzed to explain the source of the heat and bracket debonding.
Quantitative measurements are made for visualizing enamel surface before and after a self-ligating bonding technique.
Temperature rise observation during the debonding procedure - from 0.5 to 2 W power - has improved the accuracy of
assessment. The results were evaluated by CCD camera and scanning electron microscope. From the measurements it is possible to conclude that continuously running small diode pumped Tm:YAP microchip laser having output power 1W can remove the ceramic bracket without enamel iatrogenic damage.
Cr:ZnSe laser coherently longitudinally pumped with Tm:YAP microchip laser was realised.
The pumping laser consisted of Tm:YAP crystal (3x3 mm) with resonator mirrors deposited
directly on its faces (on rear face the dielectric layer with high reflectance for 1998 nm
wavelength and high transmittance for 790 nm pumping radiation wavelength; on output face
the dielectric layer with reflectance 97% at 1998 nm wavelength). The maximal output power
was 5.5 W and the generated radiation wavelength was 1998 nm. The main advantage of this
pumping was stable and still output without relaxation spikes (non-spiking).
The Tm:YAP laser radiation was collimated and focused by the set of two CaF2 lenses. The
pumping beam spot diameter inside the Cr:ZnSe crystal was 300 μm. The Cr:ZnSe laser
resonator consisted of flat rear mirror (HT at 1998 nm and HR at 2100 - 2900 nm) and curved
output coupler (r = -150 mm, R = 95% at 2100 - 2700 nm). The maximal output energy of
stable radiation was 4 mJ (pulse duration 10 ms, repetition rate 10 Hz). For wavelength tuning
the Lyott filter (quartz plate under Brewster angle) was placed between the Cr:ZnSe crystal
and output coupler. The generated radiation wavelength was continuously tunable from 2246
- 2650 nm.
The aim of our work was the application of the special sealed hollow waveguide system for the urology
treatment - In our experimental study we have compared the effects of Ho:YAG (wavelength 2100 nm) and Er:YAG
(wavelength 2940 nm) laser radiation both on human urinary stones (or compressed plaster samples which serve as a
model) fragmentation and soft ureter tissue incision in vitro. Cyclic Olefin Polymer - coated silver (COP/Ag) hollow
glass waveguides with inner and outer diameters 700 and 850 μm, respectively, were used for the experiment. To prevent
any liquid to diminish and stop the transmission, the waveguide termination was utilized.
Fe:ZnSe is one of the most promising materials capable of generating broadly tunable laser radiation in the wavelength
range from 3.5 to 5 μm. The aim of the work was to test laser properties of the Bridgman-method-grown Fe2+:ZnSe
crystal activated through the synthesis process as an active medium coherently pumped with the Q-switched Er:YAG
laser whose oscillation wavelength (2937 nm) corresponds to the maximum of the Fe2+:ZnSe absorption spectrum. The
Er:YAG laser generated giant pulses with the duration 160 - 200 ns and energy 20 - 30 mJ. The repetition-rate was set
to be 1 Hz. The oscillation properties, such as the pulse length, energy, and generated beam spatial structure, of the
Bridgman-method-grown Fe2+:ZnSe crystal used as an active medium of Fe2+:ZnSe laser operated at room temperature
were investigated. The maximal obtained output energy of room temperature Fe2+:ZnSe laser was 580 μJ for the
absorbed energy of 5.3 mJ which corresponds to slope efficiency of 38%. The generated pulse waveform was found to
follow that of the pump one.
The study demonstrates the possibility of using laser radiation for the ceramic bracket removing. Three laser radiations
were examined for this effect and the removing possibility and velocity together with enamel and root damage were
investigated. A diode pumped Tm:YAP microchip laser generating a wavelength 1.9 μm, diode pumped Nd:YAG laser
with 1.44 μm wavelength, GaAs diode with 0.808 μm were used for the debonding purpose. The measurement of
transmission and absorption of the basic element - bracket, adhesive resin, and enamel was also made with the goal to
explain the source of the heat and bracket debonding. The explanation of the debonding effect is also presented.
From the results it is possible to conclude that continuously running diode pumped microchip Tm:YAP laser having
output power 1W can be a good candidate for ceramic bracket debonding procedure.
The contemporary medicine heads towards the minimally-invasive diagnosis and treatment methods. Laser-assisted
lithotripsy is a minimally-invasive method for destroying or disruption of human urinary stones. The basic principle is
the delivery of laser light to the place of urinary stones followed by the absorprion of laser radiation by the urinary stones
material which resulted in ablation or plasma vaporization, and finished by fragmentation of urinary stones and
spontaneous draining. For the purpose of minimally-invasive laser light delivery the optical fibres or sealed and flexible
hollow waveguides are used. In this study we have compared the ablation effect of Ho:YAG laser (with the generated
wavelength 2100 nm) and Er:YAG laser (with the generated wavelength 2940 nm) on the artificial samples (special compressed plaster) and human urinary stones in vitro. The reason for the investigating of Er:YAG laser radiation is the fact that the generated wavelength 2940 nm matches the local absorption of water and therefore it is potentially applicable in various medical branches. Both lasers operated in pulsed free-running regime. The Ho:YAG laser was clinically used laser system with low-OH fibre delivery. The
Er:YAG laser was laboratory laser system and for the radiation delivery the special COP/Ag hollow glass waveguide
sealed with fused silica cap. The ablation or perforation rates were measured and compared for both laser systems,
various pulse energy levels and various interaction samples thickness. The interaction environment was water with
temperature 25°C. Finally both lasers were tested for human urinary stones lithotripsy in vitro.
We report on continuously tunable operation of a diode pumped lasers based on Tm-doped materials, emitting
in the 1.8 - 2.μ1 m spectral band. In our study we compare results obtained with three various single crystals
doped by Tm3+ ions: Yttrium Aluminum perovskite YAP (YAlO3), Gadolinium orthovanadate GdVO4, and
Yttrium Lithium Fluoride YLF (YLiF4). Following samples were available: the 3mm long a-cut crystal rod of
Tm:YAP with 4% at. Tm/Y (diameter 3 mm); the 8mm long b-cut crystal rod of Tm:YLF with 3.5% at. Tm/Y
(diameter 3 mm); the 2.7mm long a-cut crystal block of Tm:GdVO4 with 2% at. Tm/Gd (crystal face 5×3 mm).
For active medium pumping, the laser diode radiation was used. Because the tested samples differs significantly
in absorption spectra, two fibre-coupled (core diameter 400 µm) temperature-tuned laser diodes were used: first
operating at wavelength 793nm was used for Tm:YAP and Tm:YLF; the second operating at wavelength 802nm
was used for Tm:GdVO4. In both cases, the continuous power up to 20W was available for pumping. The diode
radiation was focused into the active crystal by two achromatic doublet lenses with the focal length f = 75 mm.
The measured radius of pumping beam focus inside the crystal was 260 µm. The longitudinally diode pumped
crystals were tested in linear, 80mm long, hemispherical laser cavity. The curved (radius 150mm) output coupler
reflectivity was ~ 97 % in range from 1.8 up to 2.1 μm. The pumping flat mirror had maximal reflectivity in this
range and it had high transmission around 0.8 μm. A 1.5mm thick birefringent plate made from quartz (Lyot
filter) inserted under a Brewster's angle was used as a tuning element. This plate was placed inside the resonator
between the crystal and the output coupler. Using Tm:YAP crystal, the maximal output power of 2.8W in
this set-up was obtained. The laser could be tuned from 1865nm up to 2036nm with a maximum at 1985 nm.
Laser based on Tm:YLF crystal was tunable from 1835nm up to 2010nm with a maximum at 1928 nm (3.0W
was reached). Using the Tm:GdVO4 tunable operation with greater that 1W output at 1920nm and 130nm
tuning range (1842-1972 nm) was demonstrated. The overall reached tuning range of over 200nm covers many
important atmospheric absorption lines and contains also the local absorption peak of liquid water, making them
attractive for applications such as high resolution spectroscopy, atmospheric remote sensing, laser radar, and
Laser-assisted lithotripsy is a minimally-invasive method for destroying or disruption of human urinary stones. For this
purpose laser light delivered through the flexible sealed waveguide or fibre could be utilized. On the output end of the
delivery system the laser ligth is focused onto the surface of urinary stones with various size and various composition. In
clinical urological practise the Ho:YAG laser with the generated wavelength 2100 nm operated in free-running regime is
commonly used. The aim of our investigation was to compare the damage effects of Ho:YAG laser radiation with the
promissing Er:YAG laser radiation. The Er:YAG laser generates radiation with the wavelength 2940 nm, which
coincides with the local absorption maximum of water. We have compared the laser effect with the help of uniformly
produced model samples made from special plaster. The size of the samples was 10×10×10 mm. The perforation and
disruption effectiveness of Ho:YAG and Er:YAG laser radiations were performed and compared. In the final step the
laser lithotripsy of human urinary stones was tested with Er:YAG laser radiation delivered through the special COP/Ag
hollow waveguides sealed with fused silica cap.
Cr:ZnSe laser active material is one of the favourite possibility how to generate broadly tunable mid-infrared
laser radiation at room-temperature. The aim of this study was to demonstrate and analyze pulsed as well as
continuous-wave laser action in bulk Cr:ZnSe crystals grown by the floating-zone method or by the Bridgman
method. The absorption spectra of Cr:ZnSe were measured to be from 1500 to 2000 nm, therefore various lasers
were utilized for coherent longitudinal pumping of Cr:ZnSe laser, namely flashlamp-pumped Er:YAP laser
(generated wavelength 1658 nm), diode-pumped Tm:YLF laser (generated wavelength 1912 nm), and diodepumped
Tm:YAP laser (generated wavelength 1980 nm).
In the first case, the Cr:ZnSe crystal grown by the Bridgman method was investigated. In the second case, the
Cr:ZnSe crystal grown by the floating zone method was studied. In both cases, the homogeneity of the active
Cr:ZnSe crystals was found reasonable good. The emission spectrum was from 2000 up to 2800 nm. The
Cr:ZnSe laser generated radiation was broadly continuously tunable in the range from 2050 nm up to 2750 nm.
The generated radiation beam spatial structure was close to TEM00.
Thulium doped vanadates Tm:YVO4 (5 at.% Tm/Y, grown by the Czochralski technique), Tm:GdVO4 (2 and
6 at.% Tm/Gd, grown by the floating-zone technique), and Tm:LuVO4 (3 at.% Tm/Y, grown by the floating-zone
technique) were investigated as an active medium for diode pumped tunable laser operating around 1.9 μm. For
thulium laser tuning single 1.5mm thick Brewster-angled birefringent quartz plate (Lyot filter) was placed in
simple 80mm long linear quasi-hemispherical resonator. For thulium doped vanadates pumping a fibre-coupled
(core diameter 400 μm) temperature-tuned laser diode operating in range from 799 up to 810nm was used
(max available power 20 W). All tested crystals were investigated under CW and pulsed pumping. Under pulsed
pumping (4% duty-cycle, reduced heat generation) lasing and laser tuning was demonstrated with all available
samples. Lasers were tunable in following wavelength ranges: Tm:YVO4 5 at.% Tm/Y (1841 - 1927 nm),
Tm:GdVO4 2 at.% Tm/Gd (1830 - 1982 nm), 6 at.% Tm/Gd (1850 - 2010 nm), and Tm:LuVO4 3 at.% Tm/Lu
(1860 - 1940 nm). Under CW pumping only Tm:GdVO4 crystal was lasing (lasing of Tm:YVO4 and Tm:LuVO4
was not reached under elevated pumping duty factor). Using Tm:GdVO4 (2 at.% Tm/Gd) the power up to 2.6W
and slope effciency ~ 30% (with respect to absorbed power at 808nm under lasing condition) was obtained at
wavelength 1.91 μm. Tunable operation with greater that 1W output and 130nm tuning range (1842 - 1972 nm)
was demonstrated for Tm:GdVO4 (2 at.% Tm/Gd) pumped at 802 nm.
Pulsed tunable diode-pumped Tm:YAP laser was characterized and used for preliminary investigation in eye
microsurgery. By means of Lyot filter, the laser emission was tuned between a high (120 cm-1 @ 1940 nm) and two
times lower (50 cm-1 @ 2040 nm) value of radiation absorption in water.
In the interaction experiment, the eye tissue (in vitro) was irradiated with tunable Tm:YAP laser radiation, and the effects
of cutting and coagulation depth in wavelength range from 1940 nm up to 2040 nm were investigated. The results were
documented by optical microscope.
Broadly tunable mid-infrared laser sources operated at room-temperature are desired in many technological and
medical applications. The aim of the project was to design and construct broadly tunable powerful Cr:ZnSe laser.
The investigated Cr:ZnSe various shaped bulk crystals were grown by the Bridgman method or by the floating zone method. The absorption spectrum was measured to be from 1500 to 2000 nm and the emission spectrum was from 2100 to 2800 nm. Three different lasers were utilized for coherent longitudinal pumping of Cr:ZnSe laser, namely flashlamp-pumped Er:YAP laser (generated wavelength 1660 nm), diode-pumped Tm:YLF laser (generated wavelength 1912 nm) and diode-pumped Tm:YAP laser (generated wavelength 1980 nm). The constructed Cr:ZnSe laser operated in pulsed as well as in continuous-wave regime. In the first case the Cr:ZnSe crystal grown by the floating zone method was studied. The maximal output power in continuous-wave regime was 310 mW with the slope-efficiency 73% for the Tm:YAP laser pumping. In the second case the Cr:ZnSe prism grown by the Bridgman method which served simultaneously as laser active medium and intracavity dispersive element was investigated. For the Er:YAP laser pumping the maximal output energy was 20 mJ with the slope-efficiency 36%. The output radiation was tunable in the range from 2050 nm up to 2750 nm. For the Tm:YAP laser pumping the maximal output power in continuous-wave regime was 175 mW with the slope-efficiency 24%. The output radiation was tunable in the interval from 2220 nm up to 2680 nm. The generated radiation beam spatial structure was close to TEM00.
Ceramic brackets are an aesthetic substitute for conventional stainless steel brackets in orthodontic patients. However,
ceramic brackets are more brittle and have higher bond strengths, which can lead to bracket breakage and enamel damage
during classical type of debonding.
This study examined the possibility of laser radiation ceramic brackets removing as well as the possible damage of a
surface structure of hard dental tissue after this procedure. Two types of lasers were used for the experiments - a laser
diode LIMO HLU20F400 generating a wavelength of 808 nm with the maximum output power 20W at the end of the
fiber (core diameter 400 &mgr;m, numerical aperture 0.22). As a second source, a diode-pumped Tm:YAP laser system
generating a wavelength of 1.9 &mgr;m, with up to 3.8 W maximum output power was chosen. For the investigation,
extracted incisors with ceramic brackets were used. In both cases, laser radiation was applied for 0.5 minute at a
maximum power of 1 W. Temperature changes of the irradiated tissue was registered by camera Electrophysics PV320.
After the interaction experiment, the photo-documentation was prepared by the stereomicroscope Nikon SMZ 2T, Japan.
The surface tissue analysis was processed in "low vacuum" (30 Pa) regime without desiccation. This technique was used
to record back-scattered electron images. Selecting the appropriate laser, resin, and bracket combination can minimize
risks of enamel degradation and make debonding more safe.
Free running and Q-switch infrared Er:YAG laser radiations were compared in the case of hard tissue preparation. The
interaction energy of 40 mJ in pulse 200 us long yielding to the interaction intensity 62 kW/cm2, and the energy of 20 mJ
in 100 ns long pulse yielding to the interaction intensity 62 MW/cm2 was used for the case of free running, and Q-switch
regime, respectively. For the radiation delivery, waveguide transfer system was used. It consisted of input lens (40 mm
focal length), a cyclic olefin polymer coated silver hollow glass waveguide (700/850 um diameter), and output lens (55
um focal length). For the interaction experiment the samples of the extracted human teeth cut into longitudinal sections
and polished were used. The thickness of the prepared samples ranged from 5 to 7 mm. The methods were compared
from the point of prepared cavity shape (SEM), inner surface, and possibility of selective removal of carries. The
composite filling material was used to reconstruct the cavities.
Cr:ZnSe crystals grown by the Bridgeman technique from the melt in inert gas (argon) under pressure were
characterized and utilized as effective laser active material.
Large crystalline boules with a necessary concentration of Cr2+ ions 1019 cm-3, practically homogeneously distributed
throughout the crystal bulk (50 mm in diameter and up to 100 mm in length), were prepared. For the laser evaluation
the Cr:ZnSe samples in the form of 6 mm thick blocks were polished.
Cr:ZnSe laser was longitudinally coherently pumped either with flashlamp-pumped Er:YAP laser radiation (emission
wavelength 1658 nm) or with diode-pumped Tm:YAP laser radiation (emission wavelength 1980 nm).
In the first case, the Cr:ZnSe laser was pumped with radiation of Er:YAP laser working in free-running regime (pulse
length 200 &mgr;s, pulse energy 200 mJ, repetition rate 1 Hz). The maximal obtained Cr:ZnSe laser pulse energy was 14
mJ (slope-efficiency 73%). Using the dispersive prism inside the resonator, the output laser radiation was broadly
tunable from 2150 nm up to 2600 nm.
In the second case, the Cr:ZnSe laser was pumped with radiation of diode-pumped solid-state Tm:YAP laser working
in pulsed as well as continuous-wave regime, for which the maximal obtained Cr:ZnSe laser output power was 200
mW (slope-efficiency 67%). The output spectrum of generated radiation covered the range from 2100 nm to 2400
nm. The temporal profile and spatial structure of laser beam were measured.
The Cr:ZnSe crystal grown by the Bridgeman method was demonstrated as an efficient broadly tunable laser active
material generated radiation in the mid-infrared spectrum and operated in room-temperature.
The beam spatial structure of mid-infrared laser radiation delivered by hollow glass waveguides was
investigated. As laser sources flash-lamp pumped Er:YAG, Tm:YAG, and diode-pumped Tm:YAG, Tm:YAP
laser systems generating radiation in a free-running regime were designed and constructed.
The base of transfer systems was cyclic olefin polymer-coated silver hollow glass waveguide having 700 &mgr;m
inner diameter and length up to 1.3 m. The changes of beam spatial structures through the delivery system are presented. For Er:YAG laser system the waveguide was investigated both straight and bent cases and also output laser beam stability was observed. The energy transmission characteristics were measured for all systems.
In some last years mid-infrared Er:YAG laser radiation (2940 nm) found the exploitation in many applications in technology and especially in various medical branches (dentistry, dermatology, cardiology, ophthalmology). Most of them use the Er:YAG laser system working in free-running regime generating the pulses with the length of some hundreds of microseconds. In the presented work we concentrated on the development and optimization of electro-optically Q-switched Er:YAG laser and suitable delivery system. Er:YAG laser operated both in free-running or Q-switched regime was developed and optimized. LiNbO3 Pockels cell was utilized for Q-switching the Er:YAG laser. Single giant pulses with maximal energy 67 mJ and minimal duration 53 ns FWHM were generated for maximal pump energy 131 J and for the optimal Pockels cell parameters (high voltage value 1.4 kV, delay of Pockels cell switching after the flashlamp trigger 450 μs). The Er:YAG laser radiation was effectively delivered by the special COP/Ag hollow glass waveguides with inner/outer diameters 700/850 μm or 320/450 μm, and length from 10 cm up to 1 m. The transmission of the used waveguides was measured to be from 73% to 84% according to waveguide type. With the help of delivery systems, the Er:YAG laser radiation (in the form of long pulses for free-running regime or short pulses for Q-switched regime) was applied to various biological tissue samples to study the basic laser radiation-tissue interactions and treatment possibilities.
Tunable mid-infrared laser radiation sources are of interest for many applications in spectroscopy, ranging,
remote-sensing, medical diagnosis and treatment and also for pumping nonlinear (OPO) and laser materials.
The ZnSe:Cr2+ is a promising laser active material for lasing in the range of 2-3 μm. Up to now number of
sources have been used for pumping ZnSe:Cr2+ active medium: Er-fibre laser, color-center laser, Co:MgF2
laser, Tm lasers, and Raman-shifted Nd:YAG laser [1-4].
In our study we have demonstrated, characterized and compared ZnSe:Cr2+ laser coherently pumped either
by flashlamp-pumped Er:YAP (wavelength 1.66 μm) or diode pumped Tm:YAP (wavelength 1.97 μm) laser
For the case of ZnSe:Cr2+ laser pumping by wavelength 1.66 μm, the Er:YAP laser was constructed. From
the measured output radiation characteristics followed that the maximal ZnSe:Cr 2+ laser output pulse energy
was 5.5 mJ (slope efficiency 23%), and the length of pulse 120-160 μs. With the help of dispersive prism
inside the resonator, the generated laser radiation was tunable from 2100 nm to 2450 nm with only 2 times
drop in laser efficiency. The temporal profile and spatial structure of the generated laser beam were
Consequently, the diode-pumped Tm:YAP laser was constructed for coherently pumped ZnSe:Cr2+ laser.
LIMO laser diode (40 W) was used for longitudinal pumping of Tm:YAP laser. The output characteristics
and tuning curves were measured for various ZnSe:Cr2+ laser resonator arrangements and also for various
pumping radiation conditions in pulsed regime (pulse duration, repetition rate, duty cycle).
The maximal obtained ZnSe:Cr2+ laser output pulse energy was 0.35 mJ for the Tm:YAP pump pulse energy
13.5 mJ (pulse radiation 5 ms, repetition rate 20 Hz). The generated laser radiation was tunable from 2100
nm to 2450 nm. The temporal profile and spatial structure of the generated laser beam were measured.
Er:YAG laser (wavelength 2.94 μm) operating both in free-running and Q-switched regime was designed and developed for the purpose of ureter wall perforation or incision, and urinary stones fragmentation. Component of this system was a special transfer part consisted of a cyclic olefin polymer-coated silver (COP/Ag) hollow glass waveguide (inner/outer diameter 700/850 μm or 320/450 μm) with a sealed cap for a contact treatment. Maximum pulse interaction energy and length for free-running Er:YAG laser were 100 mJ and 200 μs, respectively (corresponding intensity was 130 kW/cm2 for the 700 μm waveguide and 500 kW/cm2 for the 320 μm waveguide). Maximum interaction pulse energy and length in Q-switched regime were 30 mJ and 70 ns, respectively (corresponding intensity was 111 MW/cm2 for the 700 μm waveguide and 357 MW/cm2 for the 320 μm waveguide). Basic interaction characteristics and parameters of ureter wall perforation and urinary stones fragmentation were found. For that reason the number of pulses needed for the perforation of the ureter wall tissue (thickness ~1mm), ablation threshold and ablation rate were measured for free-running and Q-switched Er:YAG laser radiation. Subsequently, the investigated tissue samples were histologically evaluated after the interaction.
The ablation rate of the Q-switched Er:YAG laser radiation was higher compared to the free-running radiation. The application of Q-switched Er:YAG laser radiation on ureter tissue resulted in minimum tissue alteration (up to 50 μm from the surface) without any influence on the deeper layers. The possibility of urinary stones perforation with free-running Er:YAG laser radiation (with maximum interaction energy) was also demonstrated.
Hollow glass waveguide is one from a few instruments favored in industrial and medical fields for the delivery of mid-infrared laser light. The article summarizes delivery of the Er:YAG laser radiation (λ = 2.94 μm) by the cyclic olefin polymer coated silver hollow glass waveguides with various inner diameters - 320 μm, 700 μm, and 1 mm, and with length of 0.1 - 1 m. For medical applications, the so called "contact mode" in which the end of the waveguide is in contact with the soft or hard tissues is discussed. For this treatment the special sealed caps were used for preventing the waveguide system damage. Delivery of long (free-running) and short (Q-switched) mid-infrared pulses was investigated. The delivery systems were investigated for the ophthalmic, urologic, and dental tissue treatments. The comparison of interaction effects caused by the laser pulses with various lengths was made.
For the purpose of micro-selective preparation which is part of the modern dentistry four various methods were examined: ablation by Er:YAG laser radiation (free-running or Q-switching regime), preparation of tissues by ultrasonic round ball tip, and by the classical dental drilling machine using diamond round bur. In the case of Er:YAG laser application the interaction energy 40 mJ in pulse of 200 us yielding to the interaction intensity 62 kW/cm2, and 20 mJ in pulse of 100 ns yielding to the interaction intensity 62 MW/cm2 was used for the case of free running, and Q-switch regime, respectively. For comparisson with the classical methods the ultrasound preparation tip (Sonixflex cariex TC, D-Sonicsys micro) and dental driller together with usual preparation burrs and standard handpiece were used. For the interaction experiment the samples of extracted human teeth and ebony cut into longitudinal sections and polished were used. The thickness of the prepared samples ranged from 5 to 7 mm. The methods were compared from the point of prepared cavity shape (SEM), inner surface, and possibility of selective removal of carries. The composite filling material was used to reconstruct the cavities. The dye penetrating analysis was performed.
The aim of the work was to investigate the possibility of the ureter wall perforation by Er:YAG laser radiation and to explore the basic interaction characteristics for ureter surface and its deep structures. For these experiments Er:YAG laser system (wavelength 2.94 μm) working in free-running and Q-switched regime was utilized. Laser radiation was delivered to the investigated tissue by a special waveguide system. The basic part was a cyclic olefin polymer-coated silver hollow glass waveguide (inner/outer diameter 700/850 μm or 320/450 μm). Sealed cap of the waveguide was used for contact treatment. Maximum interaction pulse energy and length for free-running Er:YAG I laser with the 700μm waveguide were 100mJ and 200μs, respectively (corresponding intensity was 130 kW/cm2). Similarly the maximum interaction pulse energy and length for free-running Er:YAG II laser with the 320 μm waveguide were 80 mJ and 200 μs , respectively (corresponding intensity was 500 kW/cm2). Maximum interaction pulse energy and length in Q-switched regime were 17 mJ and 70 ns, respectively (corresponding intensity 63 MW/cm2). The number of pulses needed to perforate the ureter wall tissue (thickness ~1 mm) for using long 200 μs Er:YAG pulses (thermal ablation) and short 70 ns Er:YAG pulses (photoablation) was found. From the histological evaluation it follows that the application of Q-switched Er:YAG laser radiation on ureteral tissue resulted in minimum adjacent tissue alteration (up to 50μm from the surface) without any influence on the deeper layers.
For giant pulse generation in the mid-infrared region LiNbO3 crystal with Brewster angle cut faces was inserted inside the Er:YAG laser oscillator and a specially designed driver ensured the precise time of Pockels cell switching. The optimization of the oscillator and Pockels cell driver parameters was performed to obtain the shortest (60 ns) and stable output pulse with maximum energy (60 mJ). It gives 1 MW output peak power. Laser output dependences on the resonator parameters (resonator length and output mirror reflexivity) were also performed and the output laser characteristics well corresponded to the theoretical calculation results.
Hollow glass waveguide is one of a few instruments for the delivery of mid-infrared laser light favored in industrial and medical fields. The article summarizes delivery of the Er:YAG laser radiation (λ = 2.94 μm) by the cyclic olefin polymer coated silver hollow glass waveguides with different inner waveguide diameters (320 μm, 700 μm, 1 mm). For the medical applications, the so called "contact mode" in which the end of the waveguide is in contact with the soft or hard tissues is discussed. Delivery of free-running and Q-switched mid-infrared pulses was investigated.
The application of specially designed delivery system consisted of cyclic olefin polymer coated silver hollow glass waveguide (inner/outer diameter 700/850 μm) with protector in one side and sealed cap in the output is shown for treatment of ureter wall perforation by Er:YAG laser radiation. For this purpose Er:YAG laser system (wavelength 2.94 μm) working in free-running and Q-switched regime was utilized. The basic characteristic of the interaction of Er:YAG laser radiation with the ureter surface and its deep structures was found. Maximum interaction pulse energy and length in free-running regime were 100 mJ and 200 μs, respectively (corresponding intensity 130kW.cm-2). Maximum interaction pulse energy and length in Q-switched regime were 30 mJ and 70 ns, respectively (corresponding intensity 111 MW.cm-2). From the histological evaluation it follows that the application of Q-switched Er:YAG laser radiation on ureter tissue resulted in minimum tissue alteration without any influence on the deeper layers.
For many applications (in medicine and industry) powerful mid-infrared radiation can be useful. For this reason, Q-switch operated Er:YAG laser and corresponding delivery systems are necessary. We report about specially designed LiNbO3 Pockels cell by help of which the short 60 ns mid-infrared pulses were generated. For giant pulse generation two Brewster angle cut LiNbO3 crystal was inserted inside the oscillator and a specially designed driver ensured the precise time of Pockels cell switching. The optimization of the input parameters (high voltage value and Pockels cell switching time), which can have an impact on the output pulse characteristics, was performed. For the optimal found delay value 450 μs and the applied high voltage 1.4kV on the Pockels cell, giant pulses with length of 60 ns and energy of 60mJ were generated. It gave 1 MW of the output peak power. These powerful infrared pulses (λ= 2.94 μm) were delivered by the help of specially designed cyclic olefin polymer-coated silver hollow glass waveguide with the inner diameter 700 μm and length of 1 m. For the contact treatment sealed cap was used. The measured transmission of the whole delivery system was 76.5% which gave the output interaction intensity 79 MW/cm2.
Aim of the work was an investigation of ureter wall perforation possibility by various types of mid-infrared radiations (from 2.01 μm (Tm:YAG) up to 2.94 μm (Er:YAG)) and exploration of the interaction basic characteristic for ureter surface (epithelium) and its deep structures (mesenchym). From results follow that CTH:YAG, Er:YAG, and CTE:YAG laser radiations accomplish a good wall ureter perforation. A distinguished difference appeared in modifications of the ureter tissue - epithelium and mesenchym.
μThe study describes the preclinical experience with laser-activated bleaching agent for discolored teeth. Extracted human upper central incisors were selected, and in the bleaching experiment 35% hydrogen peroxide was used. Three various laser systems and halogen-light unit for activation of the bleaching agent were applied. They were Alexandrite laser (wavelength 750 nm and 375 nm - SHG), Nd:YAG laser (wavelength 1.064 m), and Er:YAG laser (wavelength 2.94 μm). The halogen-light unit was used in a standard regime. The enamel surface was analyzed in the scanning electron microscope. The method of chemical oxidation results in a 2-3 shade change in one treatment. The halogen-light units produced the same effect with shorter time of bleaching process (from 630 s to 300 s). The Alexandrite laser (750 nm) and bleaching agent helped to reach the desired color shade after a shorter time (400 s). Alexandrite laser (375 nm) and Nd:YAG laser had no effect on the longevity of the process of bleaching. Overheating of the chemical bleaching agent was visible after Er:YAG laser activation (195 s). Slight surface modification after bleaching process was detected in SEM.
Q-switching of mid-infrared Er:YAG laser was obtained with an electro-optical shutter. For that the LiNbO3 Pockels cell was used in transversal quarter-wave arrangement with the Brewster angle cut faces used as a polarizer. Parameters and dependences of this Q-switched system were investigated, i.e. a pulse length and generated pulse energy, delay between switching of flashlamp and Q-switch circuit, high voltage applied on Pockels cell were measured and optimized. The resulted giant pulse length and energy was 60 ns and 55 mJ, respectively. This generated pulse was obtained for the applied voltage around 1.4 kV and for the optimum delay value 450 us.
Problem of mid-infrared giant pulse delivery, which is needed for various technological applications, was solved by a specially designed cyclic olefin polymer coated silver hollow glass (COP/Ag) waveguide. Parameters of this waveguide were: diameter 700/850 um and length 1 m. The measured transmission was 74 % which corresponded to delivered intensity 86 MW/cm2.
Q-switched Er:YAG laser radiation in connection with this special delivery system gives a possibility of the surgical treatment in many medicine branches, for example ophthalmology, urology or dentistry.
Comparison of the eye tissue transmission for two (1.08 μm and 1.34 μm) Nd:YAP laser wavelengths was done. The lasers were working in pulsed free-running regime. The interaction energy of ~100 mJ and spot diameter of 5 mm was used for both wavelengths yielding in the radiation fluence ~0.51 J/cm2 (8500 W/cm2). From the step by step transmission measurement of the human eye globe layers (in vitro) was recognized that the value of the absorbed energy in particular segments was different for monitoring wavelengths yielding in the two orders fluence difference on the retina. From the results follows that the 1.34 μm radiation is absorbed mainly by the first segments of the eye in contrast to 1.08 μm for which the main part of the radiation going through all eye layers.
Generation of a giant pulse of Er:YAG laser is complicated mainly due to the properties of the Er:YAG active medium itself. It is caused by the short lifetime of the upper laser level of Er:YAG crystal and a small gain for one pass of the radiation through the active medium.
In our case, a specially designed LiNbO3 electrooptic shutter was used for Q-switching of Er:YAG laser. Brewster angles were employed at the LiNbO3 crystal faces to avoid the inclusion of a polarizer into the resonator. Even if Er:YAG crystal emission is naturally unpolarized we have found that polarization sensitive reflections at two Brewster-cut ends of Pockels cell are sufficient to reach extinction ratio necessary for giant pulse generation. By help of theoretical analysis based on Jones calculus was found the dependency of Pockels cell radiation transmission on applied voltage. Calculated transmission of Brewster-Brewster LiNbO3 Pockels cell operating in quarter-wave regime was 30% in closed state. Theoretically and experimentally was found, that for 25 mm long LiNbO3 crystal voltage 1.5 kV is sufficient for Q-switching. With described Pockels cell was realized stable running Q-switched Er:YAG laser system. The generated giant pulse length and energy was 70 ns and 30 mJ, respectively.
Short Er:YAG laser pulses were delivered by a cyclic olefin polymer coated silver hollow glass (COP/Ag) waveguide specially designed for a high power radiation. Er:YAG laser was Q-switched by an electro-optic shutter - LiNbO3 Pockels cell with Brewster angle cut input/output faces. The maximum energy output obtained from this system was 29 mJ with the length of pulse 69 ns corresponding to 420 kW output peak power. The system was working with the repetition rate of 1.5 Hz. A delivery system composed of a lens (f = 40 mm), protector and waveguide with the 700/850 μm diameter and 50 cm or 1 m length. The measured maximum delivered intensity was 86 MW/cm2 what corresponds to the transmission of 78.6 % for whole delivery system. Using of a sealed cap, this delivery system gives a possibility of the contact surgical treatment in many medicine branches, for example ophthalmology, urology or dentistry.
The success of endodontic treatment depends on the methods used
for shaping, cleaning, disinfecting, and sealing of a root canal.
In the last few decades, big progress has been achieved in the
application of the following methods: manual instrumentation,
sonic and ultrasonic devices, and rotary instruments. The
procedures used in the root canal system preparation result in a
smear layer creation. The aim of this study was to give more
precision to the smear layer removal using laser radiation. The
root canal systems of 20 human teeth were treated endodontically.
As laser radiation sources, Er:YAG laser system generating a
wavelength of 2940 nm (rep. rate 1.5 Hz, spot size diameter
320 um, number of pulses 55, energy 100 mJ) and Alexandrite
laser system generating a wavelength of 375 nm (rep. rate 1 Hz,
spot size diameter 320 um, number of pulses 200, energy
1 mJ) were used. As a delivery system, a hollow glass waveguide
with the special X-ray contrast cover was used. The flexible
waveguide was moved via root canal and the laser radiation cleaned
the wall surface. After application of Er:YAG laser radiation, the
smear layer was fully removed, the surface was clean and smooth,
and in the SEM investigation the open dentinal tubules were
visible. No cracks were determined. The surface modifications were
also not observed after endodontic preparation as well as
Alexandrite laser radiation therapy. The whole treatment can be
checked by X-ray machine.