Q-switched Nd-YAG Research Articles

Stimulated Raman scattering holography for time-resolved imaging of methane gas.

In this paper, pulsed digital holographic detection is coupled to the stimulated Raman scattering (SRS) process for imaging gases. A Q-switched Nd-YAG laser (532nm) has been used to pump methane gas (CH4) at pressures up to 12 bars. The frequency-tripled (355nm) beam from the same laser was used to pump an optical parametric oscillator (OPO). The Stokes beam (from the OPO) has been tuned to 629.93nm so that the frequency difference between the pump (532nm) and the Stokes beams fits a Raman active vibrational mode of the methane molecule (2922 cm-1). The pump beam has been spatially modulated with fringes produced in a Michelson interferometer. The pump and the Stokes beams were overlapped in time, space, and polarization on the gas molecules, resulting in a stimulated Raman gain of the Stokes beam and a corresponding loss of the pump beam through the SRS process. The resulting gain of the Stokes beam has been detected using pulsed digital holography by blending it with a reference beam on the detector. Two holograms of the Stokes beam, without and with the pump beam fringes present, were recorded. Intensity maps calculated from the recorded digital holograms showed amplification of the Stokes beam at the position of overlap with the pump beam fringes and the gas molecules. The gain of the Stokes beam has been separated from the background in the Fourier domain. A gain of about 4.5% at a pump beam average intensity of 4 MW/cm2 and a Stokes beam intensity of 0.16 MW/cm2 have been recorded at a gas pressure of 12 bars. The gain decreased linearly with decreasing gas pressure. The results show that SRS holography is a promising technique to pinpoint a specific species and record its spatial and temporal distribution.

USING Z-SCAN TECHNIQUE TO MEASURE THE NONLINEAR OPTICAL PROPERTIES OF PMMA/ZNO NANOCOMPOSITES

The study of nonlinear optical properties of polymer nanocomposites has been given increasing attention due its application in laser, communication and data storage technology. There is a need to enhance the understanding of all photonics technologies. In the current work, PMMA-ZnO nanocomposites as foils and as thin films have been successfully prepared. Casting method and spin coating were used to prepare them respectively. Nanocomposites were prepared by mixing ZnO nanoparticles with polymethyl methacrylate (PMMA) as the polymer matrix. Different contents of ZnO nanoparticles were used as the filler in the nanocomposites. The absorbance spectra of the samples were obtained. The linear absorption coefficient was calculated. The nonlinear refractive index and nonlinear absorption coefficient were investigated using a single beam Z-scan technique. A Q-switched Nd-YAG pulsed laser (532 nm, 7 ns, 5 Hz) was used as a light source. Both thin film’s and foil’s samples showed peak absorption at 375 nm and increasing absorption with ZnO nanoparticles concentration. The nonlinear refractive index was in the order of 10-11 cm2/W for thin film samples and 10-12 cm2 /W for foil’s samples with a negative sign. In contrast, the nonlinear absorption coefficient is in the order of 10-6 cm/W and 10-7 cm /W for thin film and foil respectively. The figures of merit W and T were calculated in order to evaluate the suitability of the samples as optical switching device .However; they unsatisfied the requirements of optical switching devices but they can be considered as an excellent candidate for optical limiting.

LASER TATTOO REMOVAL COMPARISON BETWEEN 1064 AND 532 NM OF A Q-SWITCHEd Nd:YAG LASER TREATMENT

Invention of the Q-switch advanced laser method is the most effective methods of tattoo removal compared to other methods of i.e. chemical, mechanical and surgical. In this study, we are reporting black pigment tattoo removal by comparing two wavelengths 532 nm and 1064 nm of Q-switched Nd-YAG laser. Using a single-pulse laser at 1064 nm wavelength, the maximum laser fluence for skin damage is 3.04 J/cm2 with pulse energy 0.55 J. While, at 532 nm wavelength, maximum laser fluence is 0.5 J/cm2 with pulse energy 0.42 J at 8-10 ns for tattooed skins. Moreover, after 1064 nm and 532 nm laser irradiations, skin biopsy of black tattooed rat’s skin demonstrates the ink granules local redistribution. Microscopic study indicates that black ink particles become smaller and vanished from the skins after 1064 nm laser treatment. The findings of this study indicate that 1064 nm wavelengths of Q-switched Nd-YAG laser treatment with 0.55 J pulse energy, is one of the significant methods of black tattoo removal with remarkable differences.

Nonlinear optical features on Yb3+/Tm3+ codoped PbO-GeO2 glasses with Si nanoparticles

Studies of third-order nonlinear optical phenomena on Yb3+/Tm3+ co-doped PbO-GeO2 glasses containing different concentration of silicon nanoparticles are presented. The well-known melting-quenching technique was used for the production of the samples. Measurements were performed using conventional Z-scan, SHG and ESHG methods with Q-switched mode-locked ns scale Nd-YAG lasers, intensities in the 0.8–1.2GW/cm2 power density range and repetition rate of 10Hz. Maximum third-order susceptibilities and second harmonic generation were found for the sample prepared with 1wt% of Si powder.

Morphologic Changes of Zebrafish Melanophore after Intense Pulsed Light and Q-Switched Nd:YAG Laser Irradiation

BackgroundRecently, the pulse-in-pulse mode of intense pulsed light (IPL) has been used increasingly for the treatment of melasma.ObjectiveTo observe the morphologic changes in the melanophore in adult zebrafish after irradiation with conventional and pulse-in-pulse IPL and Q-switched Nd:YAG (QSNY) laser.MethodsAdult zebrafish were irradiated with conventional and pulse-in-pulse mode of IPL. The conditions for conventional IPL were 3 mJ/cm2, 560 nm filter, and pulse widths of 7, 20, and 35 msec. The pulse-in-pulse conditions were 3 mJ/cm2 and on-time 1/off-time 2. The QSNY laser was used with the settings of 1,064 nm, 0.4 J/cm2, a 7 mm spot size, and one shot. Specimens were observed using a light microscope, a transmission electron microscope (TEM), a scanning electron microscope (SEM) and a confocal microscope.ResultsAfter conventional IPL irradiation with a 7 msec pulse width, melanophore breakage was observed using light microscopy. Under TEM, irradiation with conventional IPL for 7 msec and pulse-in-pulse IPL induced melanophore thermolysis with vacuolization. However, changes in the melanophore were not observed with 35 msec IPL. Under SEM, unlike the control and QSNY groups, IPL-irradiated zebrafish showed finger-like fusion in the protein structure of scales. Specimens examined by a confocal microscope after conventional IPL irradiation showed a larger green-stained area on TUNEL staining than that after pulse-in-pulse mode IPL irradiation.ConclusionZebrafish irradiated with long pulse-IPL showed no morphologic changes using light microscopy, while morphological changes in melanophores were evident with use of TEM. Pulse-in-pulse mode IPL caused less damage than conventional IPL.

基于圆环达曼光栅整形的环形光抽运的Nd:YAG声光调Q涡旋光激光器

An acousto-optically Q-switched vortex NdYAG laser by annular pumping of circular Dammann grating (CDG)shaping is investigated.The cavity of the laser is composed of a laser crystal,an acousto-optical modulator and a planar output coupling mirror.The pump source is a fiber coupling semiconductor laser of 808nm.The annular intensity distribution of pump light is formed by the first-order diffraction of a CDG with high diffraction efficiency,which is used to end pumped NdYAG laser crystal.The active Q-swith pulse laser is obtained with high optical quality,linear polarization and spiral phase.The obtained power of laser pulse is 470mW,the peak power of laser pulse reaches 588Wand pulse width is 160ns,when the absorbed pump power is 5.6Wand the frequency of acousto-optical modulator is 5kHz.

Third order nonlinearity of PMMA/ZnO nanocomposites as foils

Nonlinear optical properties have received great interests by experimentalists due to a wide range of applications in the optical devices. In the current work, the polymethyl methacrylate (PMMA)/ZnO nanocomposites have prepared as foils by using casting method. Nanocomposites have prepared by mixing the different concentrations of ZnO nanoparticles as filler with PMMA as polymer matrix. Linear transmittance spectra have investigated and linear absorption coefficients have calculated. The nonlinear refractive index and nonlinear absorption coefficient have explored by using a single beam z-scan technique, Q-switched Nd-YAG pulse laser use as the light source. The transmittance shows decrease with the increase of the ZnO nanoparticles concentration. The samples have shown peak absorption at 375 nm. The nonlinear refractive index is in the order of 10−12 cm2/W with the negative sign, whereas the nonlinear absorption coefficient is in the order of 10−7 cm/W. The real, imaginary parts and absolute value of the third-order nonlinear optical susceptibility χ(3) have calculated. χ(3) is in the order of 10−7 e.s.u. Hence, those nanocomposites indicate a promising candidate to be used as an optical limiter.

Proton beam production by a laser ion source with hydride target.

We studied proton beam production from a laser ion source using hydrogen rich target materials. In general, gas based species are not suitable for laser ion sources since formation of a dense laser target is difficult. In order to achieve reliable operation, we tested hydride targets using a sub nanosecond Q-switched Nd-YAG laser, which may help suppress target material consumption. We detected enough yields of protons from a titanium hydride target without degradation of beam current during the experiment. The combination of a sub nanosecond laser and compressed hydride target may provide stable proton beam.

Effect of Aqueous Ablation Environment on the Characteristics of ZnO Nanoparticles Produced by Laser Ablation

Effect of ablation environment on the nature of ZnO nanoparticles produced by laser ablation method in liquid medium is investigated experimentally. High purity Zn plate was irradiated by the fundamental beam of a Q-switch Nd-YAG laser in cetyltrimethylammonium bromide (CTAB), acetone, sodium dodecyl sulfate and water. Produced nanoparticles were characterized by UV–Vis absorption spectroscopy, transmission electron microscopy, scanning electron microscopy, X-ray diffraction spectrum, and fourier transform infrared spectroscopy. Results show that the highest rate of ablation occurs in CTAB. Largest nanoparticles are produced in acetone, and crystallinity of nanoparticles produced in CTAB is higher than other samples. CTAB surfactant changed the morphology of ZnO nanoparticles.

The Effect of 3 Sessions of Q Switched Neodymium: Yttrium?Aluminum?Garnet Laser in the Treatment of Freckles

Background: Freckles are common superficial pigmented lesions which can become cosmetic problems. Advances in laser technology have resulted in the ability to treat pigmented lesions with greater safety and efficacy. Objective: The study aimed to evaluate the effectiveness of 1,064 nm Q-switched neodymium: yttrium–aluminum– garnet (Nd- YAG) laser in the treatment of freckles. Methods: Fifty patients with freckles referring to the laser centers of Al-Azhar University hospital (Asyut) were enrolled in this open-label, monocentric study. All participants received 3 sessions of 1,064-nm Q switched Nd:YAG laser at 4-weeks intervals. The pigmentation area and severity index (PSI score) was calculated based on 3 parameters: Area, darkness, and density of the pigmented lesions. Results: Fifty patients (4 males and 46 females) completed the study protocol. The age of the patients ranged from 6-43 years, the duration of freckles showed a wide range, (1 month-20 years) with a mean duration of 5.13 ± 4.72 years. There was a statistical significant improvement in mean PSI after treatment of freckles with 1064 Q-Switched Nd-YAG. Excellent improvement (≥75%) were occurred in 17 cases (34%), very good improvement (50-74%) in 14cases (28%), good improvement (≥25-49%) in 16 cases (32%) and poor improvement (<25% lightening) in 3 cases (6%). The correlation between improvement and clinical parameters showed positive significant correlation with duration of disease and number of sessions. The reported side effects among this study were post-inflammatory hyperpigmentation in 2 cases (4%), hypopigmentation in 3 cases (6%) and erythema in 6 cases (12%). Conclusions: 1064 Q-switched Nd- YAG laser is effective modality in the treatment of freckles especially in patients with long duration.

Influence of sodium formate in γ-glycine single crystals – Synthesis, growth and characterization

Single crystals of γ-glycine in the presence of sodium formate were grown first time by slow evaporation method at room temperature. Crystalline nature of the material was confirmed by single crystal X-ray diffraction analysis. Solubility of the material was determined by gravimetric method. UV–Vis–NIR analysis were carried out to find the optical absorbance of the material. The presence of functional group was confirmed by Fourier Transform-Infrared analysis (FT-IR). Thermal stability and decomposition of the grown crystal were studied by Thermo gravimetric/Differential thermal analysis (TG/DTA). Energy dispersive X-ray analysis (EDAX) revealed the presence of elements in the grown crystal. The nonlinear optical response of the grown crystal was confirmed by Q-switched Nd-YAG laser and second harmonic generation efficiency of the grown crystal was found to be greater than that of KDP.

Determination of Modulus of Metal Films Using Thermoreflectance

The acoustic displacements in a film of indium pressed on to a sapphire wafer were generated by incidence of a Q-switched Nd-YAG laser beam. Acoustic displacements from tungsten film deposited on silicon substrate were also measured by the same technique. Thermoreflectance from a continuous red laser incident on the surface was used simultaneously to measure the acoustic oscillations. The acoustic oscillations were simulated using the solution to the modified wave equation. The acoustic velocity and the modulus of the metal film were determined from the simulation of the experimental results. It is shown that this technique provides a nondestructive method of determination of acoustic velocity and modulus in the metal films.

Fabrication of fiber-optic broadband ultrasound emitters by micro-opto-mechanical technology

A micro-opto-mechanical system (MOMS) technology for the fabrication of fiber-optic optoacoustic emitters is presented. The described devices are based on the thermoelastic generation of ultrasonic waves from patterned carbon films obtained by the controlled pyrolysis of photoresist layers and fabricated on miniaturized single-crystal silicon frames used to mount the emitters on the tip of an optical fiber. Thanks to the micromachining process adopted, high miniaturization levels are reached in the fabrication of the emitters, and self-standing devices on optical fiber with diameter around 350 µm are demonstrated, potentially suited to minimally invasive medical applications. The functional testing of fiber-optic emitter prototypes in water performed by using a 1064 nm Q-switched Nd-YAG excitation laser source is also presented, yielding broadband emission spectra extended from low frequencies up to more than 40 MHz, and focused emission fields with a maximum peak-to-peak pressure level of about 1.2 MPa at a distance of 1 mm from the devices.

Characterization of laser peening-induced effects on a biomedical Ti6Al4V alloy by thermoelectric means

Laser peening has recently emerged as a useful technique to overcome detrimental effects associated with other well-known surface modification processes such as shot peening or grit blasting used in the biomedical field. It is worthwhile to notice that besides the primary residual stress effect, thermally induced effects might also cause subtle surface and subsurface microstructural changes that might influence corrosion resistance and fatigue strength of structural components. In this work, plates of Ti-6Al-4V alloy of 7 mm in thickness were modified by laser peening without using a sacrificial outer layer. Irradiation by a Q-switched Nd-YAG laser (9.4-ns pulse length) working at the fundamental 1064-nm wavelength at 2.8 J/pulse and with water as a confining medium was used. Laser pulses with a 1.5-mm diameter at an equivalent overlapping density of 5000 cm−2 were applied. Attempts to analyze the global-induced effects after laser peening were addressed by using the contacting and noncontacting thermoelectric power techniques.

Optoacoustic monitoring of cutting efficiency and thermal damage during laser ablation

Successful laser surgery is characterized by a precise cut and effective hemostasis with minimal collateral thermal damage to the adjacent tissues. Consequently, the surgeon needs to control several parameters, such as power, pulse repetition rate, and velocity of movements. In this study we propose utilizing optoacoustics for providing the necessary real-time feedback of cutting efficiency and collateral thermal damage. Laser ablation was performed on a bovine meat slab using a Q-switched Nd-YAG laser (532 nm, 4 kHz, 18 W). Due to the short pulse duration of 7.6 ns, the same laser has also been used for generation of optoacoustic signals. Both the shockwaves, generated due to tissue removal, as well as the normal optoacoustic responses from the surrounding tissue were detected using a single broadband piezoelectric transducer. It has been observed that the rapid reduction in the shockwave amplitude occurs as more material is being removed, indicating decrease in cutting efficiency, whereas gradual decrease in the optoacoustic signal likely corresponds to coagulation around the ablation crater. Further heating of the surrounding tissue leads to carbonization accompanied by a significant shift in the optoacoustic spectra. Our results hold promise for real-time monitoring of cutting efficiency and collateral thermal damage during laser surgery. In practice, this could eventually facilitate development of automatic cut-off mechanisms that will guarantee an optimal tradeoff between cutting and heating while avoiding severe thermal damage to the surrounding tissues.

UV laser interaction with a fluorescent dye solution studied using pulsed digital holography

A frequency tripled Q-switched Nd-YAG laser (wavelength 355 nm, pulse duration 12 ns) has been used to pump Coumarin 153 dye solved in ethanol. Simultaneously, a frequency doubled pulse (532 nm) from the same laser is used to probe the solvent perpendicularly resulting in a gain through stimulated laser induced fluorescence (LIF) emission. The resulting gain of the probe beam is recorded using digital holography by blending it with a reference beam on the detector. Two digital holograms without and with the pump beam were recorded. Intensity maps were calculated from the recorded digital holograms and used to calculate the gain of the probe beam due to the stimulated LIF. In addition numerical data of the local temperature rise was calculated from the corresponding phase maps using Radon inversion. It was concluded that about 15% of the pump beam energy is transferred to the dye solution as heat while the rest is consumed in the radiative process. The results show that pulsed digital holography is a promising technique for quantitative study of fluorescent species.

Nucleation kinetics, growth, and optical properties of Potassium pentaborate single crystals

Single crystals of Potassium pentaborate were grown by the slow evaporation method at room temperature. Single crystal XRD provided evidence that the crystallized material was Potassium pentaborate and the lattice parameter was also ascertained. Solubility of the material was determined gravimetrically. The stability of the material was studied by observing the metastable zone width using the polythermal method. The induction period was determined at different temperatures by varying the supersaturation from 1.1 to 1.5. Various nucleation parameters such as interfacial energy, Gibbs volume free energy change, critical volume free energy change, radius of critical nuclei and nucleation rate were estimated. Optical studies were carried out in the region of 200–800nm, it was inferred that the material possessed a wide transparency in visible region with the cutoff wavelength 243nm. NLO property of the material was confirmed by Q-switched Nd-YAG technique.

Melanin index in assessing the treatment efficacy of 1064 nm Q switched Nd-Yag laser in nevus of Ota

Background:Q-switched neodymium-yttrium aluminium-garnet (Q switched Nd-Yag) laser has been used in the treatment of nevus of Ota in all skin types with variable success rate. Data with an objective assessment parameter to this laser treatment is lacking.Objective:To evaluate the utility of melanin index in assessing the treatment response and also determine the efficacy and safety of the Q-switched Nd-Yag laser (1064-nm) in the treatment of nevus of Ota in Fitzpatrick skin types IV and V.Materials and Methods:A total of 35 patients treated with Nd-Yag laser were studied. The objective improvement (pigment clearance) was determined by melanin index from two fixed points: A1, 2 cm below the pupil at the mid pupillary line (when the gaze is fixed); A2, the most prominent part of zygoma. The melanin index in these two areas was recorded as M1 and M2, respectively. The subjective clinical improvement was determined by the physician and the patient global assessment score.Results:The mean baseline melanin indices M1 and M2 were 59.54 ± 9.72 and 59.02 ± 9.16, respectively. At the last visit the mean M1 and M2 decreased to 53.8 ± 8.55 (P < 0.001) and 54.13 ± 6.01 (P < 0.001), respectively. Patient and the physician global assessment score showed that 26 (74.3%) and 20 (57.14%) patients, respectively, had >50% pigment clearance.Conclusion:The melanin index, a simple non-invasive parameter is useful in assessing the treatment response more objectively. The 1064-nm Q-switched Nd-Yag laser offers good improvement in patients with nevus of Ota in darker skin types IV/V.

Stimulated laser induced fluorescence holography for imaging fluorescent species

In this paper pulsed digital holographic detection is coupled to the stimulated laser induced fluorescence (LIF) effect for imaging fluorescent species. A frequency tripled Q-switched Nd-YAG laser (wavelength 355nm, pulse duration 12ns) has been used to pump Coumarin 153 dye solved in ethanol. Simultaneously a frequency doubled pulse (532nm) from the same laser is used to probe the solvent resulting in a gain through stimulated emission. The resulting gain of the probe beam is recorded using digital holography by blending it with a reference beam on the detector. Intensity maps were calculated from the recorded digital holograms and used to calculate the gain of the probe beam due to stimulated fluorescence emission which is coupled to the concentration of the dye. The results show that the amplification of the probe beam (532nm) due to stimulated LIF emission is seen in the intensity maps. The gain is about 40% at a dye concentration of 0.32g/L and decreases to be about 20% at a dye concentration of 0.04g/L for a probe beam energy density of 0.1mJ/cm2. Spectroscopic measurements have been carried out to confirm the holographic results. The results show that stimulated LIF holography is a promising technique for quantitative imaging of fluorescent species.

Structural, Optical and Laser Damage Threshold Studies of 1, 10 Phenanthraline Doped Potassium Penta Borate (KB5) Single Crystals

We concentrate on the low temperature slow solvent evaporation method and characterization of pure and 1, 10 phenanthraline doped KB5 and describe its potential as a non-linear optical material. The grown crystal has been subjected to single crystal X-ray diffraction analysis to identify the unit cell parameters and crystal system. The presence of carbon, hydrogen and oxygen content were confirmed by CHN analysis. The Kurtz’s-Perry powder SHG efficiency was determined for both pure and 1, 10 phenanthraline doped KB5 crystals as 1.6 and 2.2 times than that of pure KDP. Laser damage threshold studies of the pure and doped KB5 crystals have been found to be Q-Switched Nd-YAG laser.