Showing papers on "Ruby laser published in 2002"

Inducing and probing non-thermal transitions in semiconductors using femtosecond laser pulses

Abstract: Soon after it was discovered that intense laser pulses of nanosecond duration from a ruby laser could anneal the lattice of silicon, it was established that this so-called pulsed laser annealing is a thermal process. Although the radiation energy is transferred to the electrons, the electrons transfer their energy to the lattice on the timescale of the excitation. The electrons and the lattice remain in equilibrium and the laser simply 'heats' the solid to the melting temperature within the duration of the laser pulse. For ultrashort laser pulses in the femtosecond regime, however, thermal processes (which take several picoseconds) and equilibrium thermodynamics cannot account for the experimental data. On excitation with femtosecond laser pulses, the electrons and the lattice are driven far out of equilibrium and disordering of the lattice can occur because the interatomic forces are modified due to the excitation of a large (10% or more) fraction of the valence electrons to the conduction band. This review focuses on the nature of the non-thermal transitions in semiconductors under femtosecond laser excitation.

Laser hair removal: guidelines for management.

Abstract: Laser-assisted hair removal is the most efficient method of long-term hair removal currently available. Several hair removal systems have been shown to be effective in this setting: ruby laser (694nm), alexandrite laser (755nm), diode laser (800nm), intense pulsed light source (590 to 1200nm) and the neodymium:yttrium-aluminium-garnet (Nd:YAG) laser (1064nm), with or without the application of carbon suspension. The parameters used with each laser system vary considerably. All these lasers work on the principle of selective photothermolysis, with the melanin in the hair follicles as the chromophobe. Regardless of the type of laser used multiple treatments are necessary to achieve satisfactory results. Hair clearance, after repeated treatments, of 30 to 50% is generally reported 6 months after the last treatment. Patients with dark colored skin (Fitzpatrick IV and V) can be treated effectively with comparable morbidity to those with lighter colored skin. Although there is no obvious advantage of one laser system over another in terms of treatment outcome (except the Nd:YAG laser, which is found to be less efficacious, but more suited to patients with darker colored skin), laser parameters may be important when choosing the ideal laser for a patient. Adverse effects reported after laser-assisted hair removal include erythema and perifollicular edema, which are common, and crusting and vesiculation of treatment site, hypopigmentation and hyperpigmentation (depending on skin color and other factors). Most complications are generally temporary. The occurrence of hypopigmentation after laser irradiation is thought to be related to the suppression of melanogenesis in the epidermis (which is reversible), rather than the destruction of melanocytes. Methods to reduce the incidence of adverse effects include lightening of the skin and sun avoidance prior to laser treatment, cooling of the skin during treatment, and sun avoidance and protection after treatment. Proper patient selection and tailoring of the fluence used to the patient’s skin type remain the most important factors in efficacious and well tolerated laser treatment. While it is generally believed that hair follicles are more responsive to treatment while they are in the growing (anagen) phase, conflicting results have also been reported. There is also no consensus on the most favorable treatment sites.

Effectiveness of the normal-mode ruby laser and the combined (normal-mode plus q-switched) ruby laser in the treatment of congenital melanocytic nevi: a comparative study.

Abstract: The effect of the normal-mode ruby laser (NMRL) and the combined (normal mode plus Q-switched) ruby laser on congenital melanocytic nevi (CMN) was evaluated, and the degree to which both laser treatment regimens remove melanocytes was compared in 15 patients. Each nevus was marked to designate half of the lesion for the NMRL treatment and half of the lesion for combined ruby laser treatment. The efficacy of each laser treatment was correlated with the degree of clinical improvement determined by photographic assessment, histological examination, and melanin reflectance spectrometry before and 3 months after laser treatment. A single treatment using the NMRL with energy fluences of both 20 J per square centimeter and 30 J per square centimeter resulted in a slight, but not significant, improvement in lightening of pigmentation (42.61% and 30.38%, respectively). A better clinical response (excellent to good) and higher percentage of lightening (64.45%-72.43%) was noted in the combined ruby laser-treated areas than the NMRL-treated areas. Histological results showed that the combined ruby laser provided a marked decrease in the number of the nevomelanocytic nests in both the junctional area and the papillary and reticular dermis, whereas the NMRL (with energy fluences of either 20 J per square centimeter or 30 J per square centimeter) caused a decrease in the junctional area and the papillary dermis. None of the nevi had complete clearance of the pigmentation after a single treatment. Therefore, multiple (four to five) treatment sessions are needed to cause complete removal of nevomelanocytic nests in CMN. In conclusion, the combined ruby laser is more effective than the NMRL alone in the treatment of CMN without scarring or textural change of the skin.

System concept and some characteristics of the coupled-cavity laser system for active target tracking

Abstract: We performed architecture and design analyses of coupled-cavity laser systems to arrive at a concept for tracking distant objects. We also conducted an experimental study of such a system using a pulsed ruby laser as a prototype for the laboratory tests. Both laser cavities were coupled through the dynamic holographic grating. Special attention was paid to characterization of the coupled-cavity laser system and its operation. In particular, we studied the formation of holographic grating that serves to couple the cavity; the slope efficiency of the master and slave arms and their dependence upon cavity parameters. The resulted experimental data and analyses verified the tracking principle and proved the feasibility of the proposed phase-conjugate double cavity laser system for tracking moving object at distance with high accuracy.

Comparison of eye-safe UV and IR lidar for small forest-fire detection

Abstract: Lidar is a promising tool for forest-fire monitoring because this active detection technique allows efficient location of tenuous smoke plumes resulting from forest fires at their early stages. For the technique to be generally usable instrumentation must be eye-safe, i.e. it must operate within the spectral range λ 1.4 micrometers . In this paper the lidar efficiency at the wavelengths 0.3472 micrometers (second harmonic of the ruby laser) and 1.54 micrometers (Er:glass laser) are compared using a theoretical model. The results of calculations show that the energy required for smoke-plume detection using 0.3472 micrometers becomes greater than the corresponding value for 1.54 micrometers when the distance exceeds some threshold, which ranges between 2 and 6 km depending on other parameters. Being caused by relatively higher absorption of the UV radiation in the atmosphere, this result is valid for any wavelength in the vicinity of 0.35 micrometers , for example, the third harmonic of Nd:YAG laser and the second harmonic of Ti:sapphire laser.

Keyhole laser spot welding

Abstract: Physical mechanisms and quality criteria of keyhole laser spot welding partially differ from continuous laser welding, demanding separate investigations A survey on progress in laser spot welding will be given, encompassing first welds with a ruby laser in the early sixties, various industrial applications, and high speed X-ray imaging of the keyhole and mathematical modeling nowadays Numerous experimental investigations focus on parameter optimization of the pulsed laser beam in order to obtain a proper weld geometry Besides, fundamental experimental and theoretical studies have been conducted to improve understanding of the complex physical process behavior of weld defects like pore formation, cracks, spatter and undercut To control and prevent the above defects different strategies have been studied like pulse shaping or welding in the absence of ambient pressure or gravity, respectively Recently X-ray observation of the keyhole collapse in liquid Zn accompanied by transient modeling revealed some fundamentals of pore formationPhysical mechanisms and quality criteria of keyhole laser spot welding partially differ from continuous laser welding, demanding separate investigations A survey on progress in laser spot welding will be given, encompassing first welds with a ruby laser in the early sixties, various industrial applications, and high speed X-ray imaging of the keyhole and mathematical modeling nowadays Numerous experimental investigations focus on parameter optimization of the pulsed laser beam in order to obtain a proper weld geometry Besides, fundamental experimental and theoretical studies have been conducted to improve understanding of the complex physical process behavior of weld defects like pore formation, cracks, spatter and undercut To control and prevent the above defects different strategies have been studied like pulse shaping or welding in the absence of ambient pressure or gravity, respectively Recently X-

Histological changes elicited by hair removal lasers

Abstract: Several different laser systems are currently used to remove unwanted hairs. In this study, we studied follicular changes following hair removal with ruby or alexandrite lasers at different fluences. Unwanted hairs were treated with a ruby laser (ICN, Photon Ics, UK) at 10, 14, 18 J/cm(2) or an alexandrite laser (Cynosure, USA) at 11, 14, 17 J/cm(2). A 3 mm punch biopsy was taken immediately after each laser exposure and one month later. Specimens were stained for histological observations. They were observed using immunohistochemistry to Factor VIII related antigen and PCNA, and also by the TUNEL method. Immediately after the laser exposure, moderate follicular damage was observed following treatment with either laser. One month later, cystic formation of hair follicles and foreign body giant cells were observed in skin treated with either laser. The similar influence of each laser treatment resulted in similar histological changes. In this study, the histological changes following treatment with a ruby or an alexandrite laser at the same fluence were considered to be similar.

Surface waves stimulated by pulsed laser radiation in p-CdTe crystals

Abstract: The electric and photoelectric properties and the dislocation structure are studied in p-CdTe crystals after irradiation by ruby laser pulses. The dark current magnitude decreases and the dislocation densities increase both in irradiated and protected parts of the crystal. The model of a surface acoustic wave induced by a nanosecond laser pulse is used to explain the experimental results.

Assessment of patients' outcome in laser skin resurfacing

Abstract: Applications of lasers in plastic surgery and dermatology began in the early 1960's, over the last few decades many types have been developed including Ruby laser. Dye laser, Nd:YAG laser, Er:YAG laser, and Carbon dioxide laser. Carbon dioxide (CO2) laser skin resurfacing has rapidly become the treatment of choice for rejuvenation of photo-ageing skin and ablation of other skin lesions. Pulsed Erbium: Yttrium-aluminum-garnet (Er: YAG) laser skin resurfacing is currently being explored for treatment of similar skin conditions. The indications for laser skin resurfacing includes: facial wrinkling, acne scarring, scars, actinic cheilitis, some pigmented lesions, rhinophyma and benign tumours such as syringoma, trichoepithehoma, dermatosis papulosa nigra, xanthelasma, adenoma sebaceum, sebaceous hyperplasia, epidermal naevi, and others. Four mechanisms are involved in laser resurfacing: 1- Single-pulse vaporization. 2- Collagen shrinkage and skin tightening. 3- New collagen formation and remodeling of collagen. 4- Multipulse coagulation of collagen. Both the CO2 laser and the Erb:YAG laser have unique qualities that can be exploited during resurfacing. The CO2 laser is unique in the following ways: 1- Hemostasis is achieved. 2- A plateau of ablation is reached, limiting resurfacing depth if proper treatment protocols are followed. 3- Collagen (skin) tightening occurs as heat-related phenomenon, resulting in correction of loose tissue and atrophic scars. 4- The first pass causes an epidermal/dermal split that allows easy and complete removal of epidermis with a single pass. The Erb:YAG laser is unique in the following ways: 1- Minimal residual thermal damage or tissue heating occurs. 2- This pure-ablation laser continues to ablate with each pass and does not reach an ablation plateau with depth. 3- Only minimal tissue water is required for laser tissue interaction. The most successful use of lasers for skin resurfacing would be to take advantage of each laser's unique benefit and to eliminate any disadvantages as much as possible. Accordingly, a prospective study was arranged to examine the effect of Erb:YAG laser, CO2 laser, and a combined CO2-Er:YAG laser in skin resurfacing in terms of depth of injury and long term effect on histological appearances after laser skin resurfacing by each laser. Twenty patients were recruited and a skin resurfacing test patch was performed using each laser (CO2, Erb:YAG, and combined CO2/Erb:YAG) on the post auricular area. A biopsy was taken from each test patch six hours after the operation. Six months later another biopsy was taken from each test patch area of each laser (CO2, Erb:YAG, CO2/Erb:YAG) in seven patients. One year following the first operation, biopsies were taken from the test patch areas in eight other patients. Biopsies were examined histologically to determine the differences between the three lasers in terms of their effect on the histological appearance related to original depth of injury.

Formation of Two-Pulse Lasing with a Single Photoelectrical Switching of the Electro-Optical Shutter in Lasers with Anisotropic Active Elements

Abstract: We have developed an optical scheme of a laser with anisotropic active elements providing, upon a single switching of the electro-optical shutter and with the use of a bleaching filter in the cavity, the generation of double giant pulses the variation range of the time interval between which is practically unlimited. The laser provides the generation of two giant pulses whose radiation polarization planes are mutually orthogonal. An experimental study of a ruby laser of such a type with an orientation of the optical axis of the active elements close to 60° has been made.

Generation of Highly Coherent Double Giant Pulses Initiated by a Single-Shot Operation of a Photoelectrically Enabled Active Shutter

Abstract: Optical arrangements of lasers with the self-injection of initiating radiation are described. They ensure the formation of highly coherent double laser pulses with a tunable time between them upon a single photoelectrically initiated turning on of an active shutter and using a bleachable filter. The corresponding results of experimental studies of the characteristics of double-pulse radiation from this type of ruby laser are presented.

Design of touchscreen control unit for medical Q-switched ruby laser system

Abstract: The paper describes the structure of the touchscreen control unit for medical Q-switched ruby laser system, then analyzes the produced mechanism and the transmitted ways of the electromagnetic interference (EMI) noises in ruby laser system, and gives the specific methods for the EMI problems, synthetically. The analyses and methods are verified by the ultimate results of our experimentations. The conclusions and methods of the paper are useful for the design of control units in other medical and industrial lasers.

Generation of longitudinal surface acoustic waves by laser pulse

Abstract: The experimental results of excitation of longitudinal surface acoustic waves (LSAW) in solid isotropic bodies by ruby laser pulse are presented. The dependence of generation efficiency from excitation deepness under surface of propagation was investigated. Experimental measurements confirmed that LSAWs of 1 .8 MHz frequency have maximum propagation energy in (1 .5 - 2)? deepness (where ? is wavelength in solid body). It was shown that using laser pulses we can generate with high efficiency LSAW from distance in solid bodies without special processing of their surfaces. The Poisson's ratio coefficient of bodies was 0.26