Helena Jelinkova

Efficient Raman shifting of picosecond pulses using BaWO4 crystal

Abstract Stimulated Raman scattering of picosecond pulses was investigated in a new BaWO 4 Raman crystal and was compared with SRS in well known KGd(WO 4 ) 2 and KY(WO 4 ) 2 crystals. The first and second harmonic output of a mode-locked Nd:YAG laser system was used as a pump source. Due to transient behaviour, high value of BaWO 4 steady state Raman gain is reduced by a factor of 2.5 for picosecond pump pulses (28 and 40 ps) but remains still higher than that in KGd(WO 4 ) 2 crystal. Maximum first and second Stokes conversion efficiencies for BaWO 4 in a single-pass arrangement were measured to be 30% and 15%, respectively. Measurements of a temporal pulse length showed that the first Stokes pulse was twice as short as the pump pulse. Barium tungstate can thus be considered as a unique Raman crystal for wide variety of pump pulse duration from nanoseconds to picoseconds for the generation of the frequency shifted Raman laser pulses.

Near-quantum-limit efficiency of picosecond stimulated Raman scattering in BaWO 4 crystal

Stimulated Raman scattering of 35-ps pulses in BaWO(4) crystal was studied. The second harmonic of a Nd:YAG double-mode-locked laser system was used as a pump radiation source. The first Stokes conversion efficiency reached 38% in a single-pass setup and 85% in a double-pass setup. The second Stokes was generated with 20% (single-pass) and 50% (double-pass) conversion efficiency. Measurement of the temporal profiles of pump and first Stokes radiation with picosecond resolution was performed. The obtained conversion efficiency data were compared with the a plane-wave numerical model. BaWO(4) crystal can be considered an efficient Raman-active material for utilization in picosecond solid-state laser systems.

Highly efficient picosecond Raman generators based on the BaWO/sub 4/ crystal in the near infrared, visible, and ultraviolet

The stimulated Raman scattering process in a BaWO/sub 4/ crystal was employed to frequency downshift the first, second, and third harmonics of a Nd:YAG actively-passively mode-locked laser system. Single-pass, double-pass, and external cavity configurations were investigated for this purpose. In each experimental arrangement, the Stokes radiation properties were characterized regarding energy, beam profile, spectrum, and temporal development. The peak pump-to-first-Stokes conversion efficiency was measured to be 55% in the near infrared and 85% in the visible spectral region. The BaWO/sub 4/ picosecond Raman gain at a pump wavelength of 355 nm was measured to be 38 cm/GW, and a 15% conversion efficiency was achieved. A study of the Raman-cavity output beam profile development as a function of pumping energy was conducted. This work shows that the BaWO/sub 4/ crystal can be used in picosecond solid-state laser systems as an efficient frequency converter with a wide range of pump radiation wavelengths.

Efficient diode-pumped passively Q-switched Raman laser on barium tungstate crystal

Abstract An efficient all-solid-state diode-pumped intracavity Raman laser was constructed. This laser was based on three-mirror linear cavity with triangular Brewster-angle-cut Nd:YAG slab crystal pumped by 300-W quasi-CW diode Q-switched by Cr 4+ :YAG saturable absorber operated at 1064 nm. BaWO 4 (barium tungstate) crystal was used as a Raman converter. After the Raman laser optimisation for the first Stokes (1180 nm) the reproducible conversion efficiency was about 40% with respect to the Q-switched laser operation at the fundamental frequency. The corresponding output energy and pulse duration was 1.46 mJ and 3.5 ns, respectively. The top reached Raman laser output energy was 2.3 mJ with the conversion efficiency of 55%.

2-μm wavelength, high-energy Ho:YLF chirped-pulse amplifier for mid-infrared OPCPA

A 2-μm wavelength laser delivering up to 39-mJ energy, ∼10  ps duration pulses at 100-Hz repetition rate is reported. The system relies on chirped pulse amplification (CPA): a modelocked Er:Tm:Ho fiber-seeder is followed by a Ho:YLF-based regenerative amplifier and a cryogenically cooled Ho:YLF single pass amplifier. Stretching and compressing are performed with large aperture chirped volume Bragg gratings (CVBG). At a peak power of 3.3 GW, the stability was <1%  rms over 1 h, confirming high suitability for OPCPA and extreme nonlinear optics applications.

Diode-pumped Er:CaF 2 ceramic 2.7 μm tunable laser

Spectroscopic and laser properties of a newly developed high optical quality Er:CaF2 hot-formed ceramic were investigated. Under pulsed 968 nm laser diode pumping, the mid-infrared (2.7 μm) radiation was obtained with a slope efficiency of 3%. Laser tunability was reached using a birefringent filter and the laser tuning range of 118 nm, from 2687 up to 2805 nm, was demonstrated. The maximal output energy reached was 0.48 mJ at 2730 nm for the absorbed pumping energy 34 mJ.

Endodontic Treatment with Application of Er:YAG Laser Waveguide Radiation Disinfection

OBJECTIVE The objective of this study is to examine the ability of Er:YAG laser radiation. Using a movable waveguide helps to obtain an antibacterial effect, not only in root canal walls but also in the surrounding tissues. BACKGROUND DATA Conventional endodontic treatment is not fully effective due to microbial colonization of root canal walls dentin in premolars and molars. Various laser systems seem to be effective to kill the remaining microbial content in the root canal. The problem is in the flexibility of laser system tips. MATERIALS AND METHODS The Er:YAG laser system was designed with a fluorocarbon polymer-coated silver hollow glass waveguide. Root canal systems of 44 premolars and molars were treated endodontically, using a step-back technique; 10 teeth were then treated with calcium hydroxide paste, and 22 teeth were irradiated by a movable waveguide. Before and after treatment, the colony-forming units were counted to determine 21 various microorganisms. RESULTS Classical enlargement and shaping of the root canal is effective in 60%. Application of calcium hydroxide prepares sterile root canal in 80%. Er:YAG laser irradiation via movable waveguide (energy of 100 mJ, 30 pulses, repetition rate 4 Hz) can ensure residual disinfection of the root canal. CONCLUSION Application of Er:YAG laser radiation through a flexible waveguide helps to attain antibacterial effect, not only in the root canal walls, but also in the surrounding tissues. Therapeutic doses of laser radiation guarantee one-step disinfection, including of anaerobic microorganisms.

Erbium:YAG laser lithotripsy by use of a flexible hollow waveguide with an end-scaling cap.

An Er:YAG laser light delivery system composed of a polymer-coated silver hollow waveguide and a quartz sealing cap has been developed for calculus fragmentation. Sealing caps with various distal-end geometries were fabricated, and the focusing effects of these caps for Er:YAG laser light were measured both in air and in water. Owing to the high power capability of the quartz a beam of sealing caps, Er:YAG laser light with an output energy of 200 mJ and a repetition rate of 10 Hz was successfully transmitted in saline solution by use of the system. Calculus fragmentation experiments conducted in vitro showed that the delivery system is suitable for medical applications in lithotripsy. We also found that the cap with a focusing effect is more effective in cutting calculi. The deterioration of the sealing caps after calculus fragmentation is also discussed.

Ceramic Bracket Debonding by Tm:YAP Laser Irradiation

OBJECTIVE The aim of this study was to prepare a simple and reliable method for ceramic bracket debonding, ensuring minimal changes in the enamel structure and an acceptable temperature rise in the pulp. BACKGROUND DATA Ceramic bracket debonding is based on the principle of degrading the strength of adhesive resin between the tooth and ceramic bracket. The search for a safe and efficient method of adhesive resin removal following debonding has resulted in the introduction of a wide range of instruments and procedures, among which proper use of laser irradiation can be promising. METHODS The debonding of two types of ceramic brackets utilized a diode-pumped Thulium:Ytterbium-Aluminium-Perovskite (Tm:YAP) microchip laser generating irradiation at a wavelength of 1998 nm (spot size 3 mm; focused by lens), with two power settings (1-2 W). Loss of enamel and residual resin on teeth, as well as rise in temperature inside the tooth were subsequently investigated in detail. RESULTS A 1W power of irradiation during a 60-sec period resulted in a temperature rise from 3 to 4°C in the approximate root location. This power is also suitable for debracketing from the point of view of damage to enamel lying below the bracket. Only a slight damage to the enamel was registered by SEM compared to conventional bracket removal. CONCLUSIONS Use of a Tm:YAP laser (wavelength 1998 nm, power 1 W, irradiance 14 W/cm(2), interacting time 60 sec) which is at the same time compact and small enough to be used in the dental practice, together with moderate cooling, could be an efficient tool for debracketing.

Penetration of high-intensity Er:YAG laser light emitted by IR hollow optical fibers with sealing caps in water

The penetration depth in water was measured for Er:YAG laser light in a high density relevant to clinical applications. Various types of focusing elements were used to guide the light efficiently. We found that the transmission distance depended strongly on the beam shape in the water. When we used a plano-convex type of focusing cap, the penetration depth was larger than that when a dome- or ball-type cap were used.