Q-switched Laser Radiation Research Articles

Opacity Corrections for Resonance Silver Lines in Nano-Material Laser-Induced Plasma

Q-switched laser radiation at wavelengths of 355, 532, and 1064 nm from a Nd: YAG laser was used to generate plasma in laboratory air at the target surface made of nano-silver particles of size 95 ± 10 nm. The emitted resonance spectra from the neutral silver at wavelengths of 327.9 nm and 338.2 nm indicate existence of self-reversal in addition to plasma self-absorption. Both lines were identified in emission spectra at different laser irradiation wavelengths with characteristic dips at the un-shifted central wavelengths. These dips are usually associated with self-reversal. Under similar conditions, plasmas at the corresponding bulk silver target were generated. The recorded emission spectra were compared to those obtained from the nano-material target. The comparisons confirm existence of self-reversal of resonance lines that emerge from plasmas produced at nano-material targets. This work suggests a method for recovery of the spectral line shapes and discusses practical examples. In addition, subsidiary calibration efforts that utilize the Balmer series Hα-line reveal that other Ag I lines at 827.35 nm and 768.7 nm are optically thin under variety of experimental conditions and are well-suited as reference lines for measurement of the laser plasma electron density.

Sum frequency conversion of multiline CO laser emission in BaGa2GeSe6 crystal of one cm long

Sum frequency conversion of multiline Q-switched CO laser radiation was studied in 10.4mm-long BaGa2GeSe6 crystal under noncritical spectral phase-matching conditions. Spectrum of the CO laser consisted of 51 emission lines in the wavelength range of 4.95-6.20 μm. The frequency converted spectrum contained 85 spectral lines in the wavelength range of 2.5-2.8 μm. The internal energy conversion efficiency (taking into account optical losses on uncoated facets of the crystal) was up to 1.7%.

Sum-frequency generation of Q-switched CO laser radiation in BaGa2GeSe6 and GaSe nonlinear crystals

Sum-frequency generation of multiline Q-switched CO laser radiation is studied in the BaGa2GeSe6 (BGGSe) crystal and in the GaSe crystal. The maximal external conversion efficiency obtained in the BGGSe crystal is 0.7%, which corresponded to the internal conversion efficiency of 1% taking into account optical losses under reflection from uncoated facets of the crystal. The maximum external conversion efficiency in the GaSe crystal is 0.15% with internal efficiency 0.31%. Effective nonlinearity of BGGSe crystal is determined through the ratio between measured efficiency in BGGSe and GaSe crystals. Effective nonlinearity for sum-frequency generation of the CO laser emission in the BGGSe crystal is deff = 42 ± 14 pm/V, and nonlinear coefficient of this crystal is d11 = 49 ± 15 pm/V.

Sum frequency generation under conversion of Q-switched cryogenic slab RF discharge CO laser radiation in ZnGeP2

For the first time broadband sum frequency generation in ZnGeP2 crystal has been accomplished with a compact cryogenic slab RF discharge CO laser. The spectrum of the CO laser operating in a repetitively pulsed multiline Q-switching mode consisted of ~90 emission lines in the wavelength range of 4.95–6.60 µm. Internal sum frequency generation efficiency was reached up to 8.2%. The resulted spectrum contained ~200 spectral lines in the wavelength range of 2.5–3.2 µm.

Control of Q-switched laser radiation characteristics via changing the gain distribution

The advantages of simultaneous side and end diode pumping of Nd:YAG laser to enhance the spatio-temporal characteristics in the Q-switched mode of operation has been demonstrated. It has been shown that using a hybrid pump geometry in a short linear resonator provides a superior combination of output beam optical quality, energy, and pulse duration in contrast to the solitary use of an end-pump or a side-pump scheme at similar levels of average output power. We have demonstrated a compact single active rod Nd:YAG laser design in Q-switching mode with a pulse duration of 18 ns, pulse energy up to 3mJ, a repetition rate of 8 kHz, and М2 <2.

Spectral characteristics of multi-line Q-switched CO laser radiation frequency converted in ZnGeP2

Lasing on different spectral lines belonging to a giant pulse of multi-line Q-switched CO laser was experimentally studied. The Q-switched CO laser emitted a giant microsecond pulse that consisted of about one hundred subpulses corresponding to different rotational–vibrational transitions. Amplitude, time delay and duration were measured for such a laser subpulse, and processes affecting formation of the CO laser giant pulse spectrum were analyzed. These data were taken into account to correctly estimate peak power and the number of spectral lines of radiation formed under sum frequency conversion of the CO laser radiation in nonlinear ZnGeP2 crystal.

Frequency conversion of mode-locked and Q-switched CO laser radiation with efficiency up to 37%.

Frequency conversion of CO laser radiation was experimentally studied in ZnGeP(2) and GaSe nonlinear crystals. To enhance conversion efficiency, we applied a CO laser system "master oscillator power amplifier" with concurrent mode locking and Q switching. The laser system emitted ∼1-μs train of ns pulses. Internal efficiency of frequency doubling reached 37% in ZnGeP(2) crystal and 5% in GaSe crystal. Two-stage frequency conversion (including second-harmonic and difference-frequency generation) in ZnGeP(2) crystal under optical pumping by a selective two-spectral line CO laser was studied.

Successful Treatment of Cosmetic Mucosal Tattoos Via Q-Switched Laser

Tattoo removal using Q-switched lasers is well established in the medical literature, but it is not clear how tattoos on mucosal membranes should be treated because of their infrequent presentation. To report successful cosmetic tattoo removal using Q-switched laser irradiation on the oral mucosal surface. Three men with cosmetic tattoos on the orolabial mucosa of the lower lip sought permanent removal. Each patient received treatments using a Q-switched neodymium-doped yttrium aluminum garnet (Nd:YAG) laser to the desired endpoint. Treatment of the affected area with the Nd:YAG laser resulted in clearing of the pigment without scarring. Q-switched laser treatment is a safe and very effective means of removing cosmetic mucosal tattoos on the inner lip and should be considered the criterion standard treatment option.

Comparison of Two Q-Switched Lasers and a Short-Pulse Erbium-Doped Yttrium Aluminum Garnet Laser for Treatment of Cosmetic Tattoos Containing Titanium and Iron in an Animal Model

Cosmetic tattoos contain titanium and ferric oxide and darken through reduction after Q-switched laser irradiation. The optimal treatment for removing these pigments remains unknown. To compare the effects of two Q-switched lasers and a short-pulse erbium-doped yttrium aluminum garnet (SP Er:YAG) laser to remove cosmetic tattoos in an animal model. Rats were tattooed using white, flesh-colored, and brown inks (4 bands of each color) on their backs. For each color, one band was left untreated, and one each was treated with a Q-switched neodymium-doped YAG laser, a Q-switched alexandrite laser, and a SP Er:YAG laser every 3 weeks until the pigments were clear. The two Q-switched lasers were equally effective; all three pigments darkened initially and then resolved gradually. Up to 20, 18, and 10 sessions were required to remove white, flesh-colored, and brown tattoos, respectively. Only six sessions were required with the SP Er:YAG laser. Minimal scarring was observed with all lasers. Skin biopsies confirmed pigment granule fragmentation after Q-switched laser treatment and a decrease in the amount of pigment after SP Er:YAG laser treatment. The SP Er:YAG laser was superior to the Q-switched lasers for removing cosmetic tattoos.

An investigation of the synthesis of metallic nano-particles by laser ablation

A numerical model is proposed to simulate the deposition process of the metallic particles under laser irradiation, in order to investigate the formation mechanism of the nano-particles for the mass production. The deposition of nano-particles has been effectively made by a Q-switched laser irradiation of nickel substrate. In the analysis of the localized ablation phenomenon, which was induced by a high peak power laser, the deposition of nickel nano-particles with narrow size distribution has been examined. The analysis of fabrication mechanisms has been studied for the process design from the macroscopic to microscopic views and the process characteristics of the laser ablation for the nano-particle deposition has been verified experimentally and numerically.

Material processing with pulsed radially and azimuthally polarized laser radiation

We report on the generation of radially and azimuthally polarized Q-switched laser radiation and its application in material processing. The power levels were sufficiently high to study micro-hole drilling in different metals. Depending on the optical properties of the metal, either radial or azimuthal polarization shows the best efficiency and the effect is attributed to waveguiding. For steel, a comparison to linearly or circularly polarized laser radiation indicates that the doughnut-shaped beam with azimuthal polarization is the most energy-efficient in producing holes of the same diameter and depth.

Intense Pulsed Light Therapy for Superficial Pigmented Lesions Evaluated by Reflectance-Mode Confocal Microscopy and Optical Coherence Tomography

Intense pulsed light (IPL) therapy is reported to be effective for pigment removal from pigmented lesions. However, the dynamic mechanism of pigment removal by IPL therapy is not completely understood. We investigated the mechanism of IPL therapy for the removal of pigmented skin lesions through non-invasive observation of the epidermis. Subjects with solar lentigines on the face were treated with three sessions of IPL therapy. The solar lentigines were observed on consecutive days after the treatments using reflectance-mode confocal microscopy (RCM) and optical coherence tomography (OCT). In addition, desquamated microcrusts that formed after the treatment were investigated by transmission electron microscopy (TEM). The images of RCM and OCT showed that the melanosomes in the epidermal basal layer rapidly migrated to the skin surface. The TEM images of the extruded microcrusts revealed numerous melanosomes together with cell debris. It was also found that the IPL irradiated melanocytes in the lesions seemed to be left intact and resumed their high activity after treatment. We conclude that IPL therapy effectively removed the dense melanosomes in the epidermal-basal layer. However, additional application of suppressive drugs such as hydroquinone or Q-switched laser irradiation is necessary to suppress the remaining active melanocytes.

Optical Properties of Bismuth Triborate (BIBO) Single Crystals

We present a study of the nonlinear optical and elasto-optic properties of BiB 3 O 6 (BIBO) crystal. The estimated values of the nonlinear optical coefficients d ij are compared with the previously published values. Efficiency of the phase matched SHG and optical damage threshold for Q-switched Nd-YAG laser radiation are reported as well. The elastooptic constants p ij corresponding to the acoustic phonons propagating in q = [100], q = [010], q = [001], q = [110], q = [101] directions were estimated using Brillouin scattering method.

Analysis of the laser-induced reduction mechanisms of medieval pigments

This study is concerned with the effect of infrared Q-switched laser radiation on four of the most commonly used medieval pigments. Vermilion, red lead (minium), white lead and yellow lead (massicot) have been irradiated with Nd:YAG laser radiation at 1064 nm. Visual observation, reflectance spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy analyses have been employed to study the colour alteration, identity the chemical composition and observe the surface of the irradiated pigments. It was shown that, contrary to what was generally accepted, the mechanism responsible for the discoloration is reduction. It was suggested that under the intense laser ablation conditions and the plasma formation, oxidation is not favourable and instead the pigments decompose to their constituent elements. This scenario can also explain the temporary blackening on red and white lead as it is a well established tendency for metallic lead to become oxidised as soon as favourable conditions are obtained. Recovery mechanisms are currently being studied to prove the model.

LASER TREATMENT OF TATTOOS

All three Q-switched laser systems can effectively remove most tattoos with minimal scarring or other adverse sequelae. Despite advances in laser technology, all tattoos cannot be completely eliminated, and several wavelengths remain necessary to optimally treat multicolored tattoos. The major advantage of Q-switched laser irradiation to effect tattoo removal is the low risk of scarring associated with treatment. Limitations include the need for multiple treatment sessions, minimal to incomplete responses in some cases, and the possibility of pigmentary and textural changes. Research continues in an effort to perfect laser removal of tattoos.

Mechanism of dye-enhanced pulsed laser ablation of hard tissues: implications for dentistry

Alexandrite laser ablation of enamel enhanced by an indocyanine green dye was studied. A microjet system was employed to deliver precisely measured small amounts of absorbing dye solution to the site of irradiation. A sequence of physical phenomena involved in dye-enhanced laser ablation of dental enamel was revealed when laser pulse profiles were compared with the profiles of laser-induced pressure, laser-induced plasma, and ablation plume kinetics. To understand photomechanical effects on the enamel ablation, the absolute values of pressure waves were measured by a calibrated wide-band acoustic transducer. Absolute amplitude and temporal profile of pressure waves, plasma emission, ablation plume kinetics, ablation efficiency, and crater quality under free-running and and Q-switched ablation of enamel were studied. It was found that there is an optimal dye solution volume (100-200 nL) when the maximum ablation efficiency (30 μm/pulse) can be obtained. It was shown that the ablation efficiency under Q-switched laser irradiation is approximately one order of magnitude lower than that under free-running ablation. It was shown that Q-switched enamel ablation with dye solution is caused by the powerful recoil pressure wave with an amplitude 3-6.5 kbar. In contrast, dye-enhanced free-running enamel ablation is caused by plasma-mediated evaporation of enamel and accompanied by recoil pressure waves of lower amplitude (0.5-1 kbar) that is below mechanical damage threshold in enamel. Uneven crater walls after Q-switched ablation were observed by scanning electron microscopy (SEM). Free-running ablation makes precise craters with smooth and even crater walls.

Modulation of alpha 4 beta 1 and alpha 5 beta 1 integrin expression: heterogeneous effects of Q-switched ruby, Nd:YAG, and alexandrite lasers on melanoma cells in vitro.

Integrins of the beta 1 family are cellular adhesion molecules that play an important role in cell attachment and migration by interacting with extracellular matrix molecules. Agents such as hormones, cytokines, and ultraviolet radiation have all been shown to have an integrin modulating potential. The present study indicates that radiation of Q-switched lasers is also able to induce transient changes in integrin expression levels on human melanoma cells in vitro. Radiation from Q-switched Ruby (694 nm), Alexandrite (755 nm), and Nd:YAG laser (1,064 nm) with fluences comparable to those that are generally used in treating dermatologic lesions were used to irradiate a subconfluent layer of human melanoma cells. After fixed time intervals, the cells were harvested either to analyse the integrin expression by flow cytometry or to investigate changes in cell attachment, spreading, and migration. It was established that all three types of laser were able to cause a significant downregulation of both the alpha 4 and the common beta 1 integrin subunit. The Alexandrite and Ruby lasers also induced a decrease in alpha 5 expression; however, the cells treated with the Nd:YAG laser showed a marked upregulation of the alpha 5 subunit. The expression of the other beta 1 integrin subunits was shown to be unaltered after laser treatment. Downregulation of the alpha 4 upregulation of the alpha 5 integrin subunit expression resulted in, respectively, decreased and increased attachment and spreading on fibronectin, the extracellular matrix ligand for both the alpha 4 beta 1 and alpha 5 beta 1 integrins. Marked upregulation of the alpha 5 subunit also resulted in a higher migration rate. Taken together, these results show that nonlethal doses of Q-switched laser radiation are able to induce changes in cellular behavior in vitro by modulating the integrin expression pattern.

Plasma detection of laser field interaction with optical thin films

Plasmas produced in Q-switched laser irradiation of two types of single-layer optical coatings are detected, and the field effect in this interaction process is analyzed.

Trapping of Au in Si during pulsed laser irradiation: A comparison with ion beam induced segregation

Liquid phase nonequilibrium segregation and trapping of Au in Si induced by Q-switched laser irradiation are reported. Depending on the incident laser energy density, irradiation results in either amorphization or recrystallization of a near surface layer. In the latter case, at interface velocities of 9 m/s, the segregation coefficient is 0.1±0.02 and Au is trapped in near-substitutional lattice sites at concentrations of 0.5 at. %. These results are compared with recent data on solid phase, ion beam induced segregation, where Au at the amorphous-crystal interface is trapped on nonunique lattice sites.

Studies of Ultra-High Speed Silicon Crystal Growth From The Melt By Use of Conventional and High Resolution Transmission Electron Microscopy

Fast melting and solidification of semiconductors by use of Q-switched laser irradiation techniques has provided, during the last few years, a large amount of information on novel high speed crystal growth processes. Under the highest quench rate conditions, the motion of the final solidification interface can be so rapid (many metres per second) that atomic ordering processes are overwhelmed and either defective crystal or even the amorphous solid phase is formed. Most work in this area has been carried out on elemental Si and electron microscopy of solidification structures has played an essential analytical role through both conventional and high resolution imaging studies. The present paper will outline recent progress which has been made in understanding the crystallographic orientation dependence of high-speed growth phenomena.