355nm UV Laser Research Articles

High conversion efficiency and extra-cavity sum frequency 355nm UV laser output

Currently, the common method to obtain ultraviolet laser is an all-solid-state laser combined with nonlinear frequency conversion technology, which generates three, four or five harmonics outside or inside the resonator cavity through the frequency conversion of near-infrared light waves around 1.0μm. Ultraviolet light sources are mainly obtained in two bands of 355mm and 266nm. Ultraviolet laser is characterized by high photon energy, short wavelength, cold treatment and good focusing performance, be widely used in the fields of medicine and biology, industrial microprocessing, atomic/analytical spectroscopy and chemical dynamics, environmental detection and atmospheric detection. In this article, we put forward with two sum frequency crystals to obtain UV laser, based on the method of theoretical analysis and experiment validation, Nd:YAG crystal was used as a gain medium to generate 1064 nm laser, double frequency generated 532 nm green laser by KTP crystal, 1064 nm and 532 nm throughed two sum frequency crystals and frequency conversion outside the cavity. The High conversion efficiency and high peak power 355nm ultraviolet light output is realized.

Fabrication of a high-density nano-porous structure on polyimide by using ultraviolet laser irradiation

A new approach for fabricating a high-density nano-porous structure on polyimide (PI) by using a 355-nm UV laser is presented here. When PI was irradiated by using a laser, debris that had electrical conductivity was generated. Accordingly, that debris caused electrical defects in the field of electronics. Thus, many researchers have tried to focus on a clean processing without debris. However, this study focused on forming a high density of debris so as to fabricate a nano-porous structure consisting of nanofibers on the PI film. A PI film with closed pores and open pores was successfully formed by using a chemical blowing agent (azodicarbonamide, CBA) in an oven. Samples were precured at 130 °C and cured at 205 °C in sequence so that the closed pores might not coalesce in the film. When the laser irradiated the PI film with closed pores, nanofibers were generated because polyimide was not completely decomposed by photochemical ablation. Our results indicated that a film with micro-closed pores, in conjunction with a 355-nm pulsed laser, can facilitate the fabrication of a high-density nano-porous structure.

UV laser direct texturing for high efficiency multicrystalline silicon solar cell

Surface texturing is a technique used to increase light-trapping by forming certain structures on surface of a photovoltaic cell. We performed direct surface texturing using a 355nm UV laser to create V-shaped grooves on p-type, boron-doped multicrystalline silicon wafer of 200μm thickness. In addition, a 1064nm fiber laser was used to fabricate U-shaped grooves; this was done to determine the effect of light-trapping according to the shape of the structure. The samples were processed by 25% NaOH and acid solutions to remove slag after the direct texturing and isotropic etching. The reflectance and minority carrier lifetimes were measured to analyze the effects of the V-shaped groove and U-shaped groove. The V-shaped groove sample without the etching process showed 8.6% reflectance, while the sample etched for 4min with NaOH and 4.5min with isotropic acid after the laser texturing showed 13.2% reflectance. The minority carrier lifetime of the UV laser, V-shaped groove sample increased from 2.6μs to 20.6μs while that of the fiber laser, U-shaped groove sample increased from 2.3μs to 5.9μs. Etching was essential to remove slag and damages from the laser processes since these defects can induce inefficient electrical performance, as in long carrier lifetime. However, excessive etching flattens the surface and results in reduced effectiveness of light trapping. Consequently, the densely-packed V-shaped textures were more effective for capturing photons than the U-shaped texture.

Laser forward transfer based on a spatial light modulator

We report the first demonstration of laser forward transfer using a real-time reconfigurable mask based on a spatial light modulator. The ability to dynamically change the projected beam shape and size of a coherent light source, in this case a 355-nm pulsed UV laser, represents a significant technological advancement in laser direct-write processing. The application of laser transfer techniques with adaptive control of the laser beam pattern is unique and represents a paradigm shift in non-lithographic processing. This work describes how the size and shape of an incident laser beam can be dynamically controlled in real time with the use of a digital micromirror device (DMD), resulting in laser-printed functional nanomaterials with geometries identical to those of the projected beam. For applications requiring additive non-lithographic techniques, this novel combination, which relies on the laser forward transfer of variable, structured voxels, represents a dramatic improvement in the capabilities and throughput of laser direct-write processes.

Synthesis, characterization, and antimicrobial application of nano-palladium-doped nano-WO 3

Nano-tungsten trioxide ( n-WO 3) was synthesized by dehydrating tungstic acid (H 2WO 4) at 300 °C. Nano-palladium ( n-Pd) was then loaded as 10 wt% on this n-WO 3 by impregnation for the synthesis of the desired n-Pd/ n-WO 3 photocatalyst. This loading process enhanced the photocatalytic activity of n-WO 3 for the removal of Escherichia coli microorganism from water when applying 355-nm UV laser radiation. The absorption and photoluminescence spectra revealed a blue-shift for the band gap energy ( E g ) from 2.71 eV for the undoped n-WO 3 to 3.5 eV for the doped one. This shift in E g caused a near resonance condition, which accounts for the significant improvement of the photocatalytic activity upon doping n-WO 3.

Enhanced stimulated Raman scattering in H2 by seeding an SRS line into an H-ɛ Balmer line: Amplification-coupled laser wavelength shifter

The stimulated Raman scattering (SRS) in H2 gas above the dissociation energy limit was recorded using a 266-nm UV laser. All of the observed Stokes and anti-Stokes SRS lines showed a normal behavior except the third Stokes SRS lines at 397.8 nm, which showed a substantial intensity enhancement of about a 36%-conversion efficiency of the pump energy. This enhancement in the SRS line is attributed to the seeding of the SRS line into the Balmer H-ɛ line at 397 nm in molecular hydrogen. To the best of our knowledge, there is no report of any work on enhanced stimulated Raman scattering in H2 by the seeding of the H-ɛ Balmer line into the SRS line and attaining a very high intensity at the third Stokes SRS lines at 397.8 nm. The cell pressure and the laser pulse energy dependence of these SRS lines substantiate our explanation.

Using Volatile Solvents for Ion Formation in Liquid Molecular Beam Expansion Mass Spectrometry

Cocrystallization between analyte and matrix is required by matrix-assisted laser desorption/ionization and can represent a significant limitation of the technique. A molecular beam expansion, mass spectrometric method has been developed to explore the possibility of using pure solvents as matrix to avoid cocrystallization. Two kinds of solvent, liquid CS2 and liquid or supercritical CO2, have been studied with 266-nm UV laser irradiation. We successfully ionized a number of compounds, including caffeine, guanine, cholesterol, and mixed fullerenes. Under some conditions, the mass spectra reflect parent radical cations formed by photoionization. Under other conditions, protonated, sodiated (and with CS2 even sulfated) ions are seen reflecting a nonunimolecular ionization process. When UV-transparent CO2 is used as a solvent, only analyte molecules with a UV chromophore are detected. However, with UV-absorbing CS2, we demonstrate ionization of molecules lacking a UV chromophore. This work provides strong evidence that one can form solvent clusters containing analyte, that laser photoionization of the solvent precedes ionization of the analyte, and that solvent evaporation along with the indirect ionization leads to reduced parent ion fragmentation. The exploration of this now demonstrated concept with other solvents would appear fruitful for future work.

Near-field optical patterning on chloromethylated polyimide

Near-field scanning optical microscopy (NSOM) coupled with laser is used in nano-scale processing to make nano-scale dots or nano-scale structure. Nano-sclae processing using NSOM coupled with laser can be applied to photo- chemical etching process on crstalline silicon, to additive processes on some polymers, to subtraction processes on SAMs and other polymers. And it can be used to change material's optical properties in nano-scale geometry. As above, nano-scale processing using NSOM coupled with laser has an advantage that it can be applied to various processes. In this work, by using NSOM coupled with 266㎚ UV laser, nano-scale patterns were fabricated on chloromethylated polyimide(CMPI) films coated on silicon wafer. CMPI undergoes a fast photolysis under UV light. So, in the case of pattern fabrication on CMPI it is possible to fabricate patterns without development process. Possibilities for SMPI to be applied to nano-scale patterns fabrication were demonstrated. Compared to usual lithographic processes, the process proposed in this work is simple because development, one of steps to fabricate nano-scale patterns, is not needed. And the finite-difference-time-domain(FDTD) method was employed to simulate the energy intensity distribution in the near-field. The simulation was executed for NSOM tip and UV laser. The influence of aperture size and tip-sample distance on the resolution of the lithographic process is discussed from the simulation results. Comparison of some simulation results with corresponding experimental results could confirm the validity of the simulation model proposed.

Laser-diode pumped Nd: GdVO4 ultraviolet laser with LBO frequency tripling

We have demonstrated a laser-diode pumped Nd: GdVO4 extra-cavity frequency tripling ultraviolet laser with a LBO crystal in this paper. Under the acousto-optic (A-O) Q-switched operation, we have obtained 355 nm ultraviolet laser, with pulse width of 25 ns and pulse repetition rate of 20 kHz. By using a type I non-critical phase-matched LBO crystal, the SHG output power of 822 mW is achieved at the incident pump power of 16 W. The output power of 355nm UV laser is 260mW with a type II phase-matched LBO crystal, and the conversion efficiency (1 064 nm-355 nm) is 5.9 %. The power stability of 355 nm laser is 1.7% in 1 h.

Rapid quantitative analysis of Y and REE abundances in XRF glass bead for selected GSJ reference rock standards using Nd-YAG 266nm UV laser ablation ICP-MS.

We have developed a rapid and precise analytical technique for the determinations of Y and rare earth elements (REE) from silicate rock samples by preparing XRF glass beads and using laser ablation (LA)ICP-MS. Combined with XRF analysis, abundances of 39 major and trace elements (Al, Ca, Fe, K, Mg, Mn, Na, P, Si, Ti; Ba, Ce, Co, Cr, Dy, Er, Eu, Ga, Gd, Ho, La, Lu, Ni, Nb, Nd, Pb, Pr, Rb, Sc, Sm, Sr, Tb, Th, Tm, V, Y, Yb, Zn, Zr) for around 30 powder samples of silicate rocks can be measured successfully within five days. The method was applied to twelve GSJ rock reference materials (JA-1, JA-2, JA-3, JB1a, JB-2, JB-3, JG-1a, JG-2, JG-3, JGb-1, JR-1 and JR-2) to assess the precision and accuracy of our data. The data obtained from the GSJ rock reference materials reveals that most of the data ranging from the mafic to intermediate rock materials show good agreement with the compiled values reported by Imai et al. (1995) within ±20%. Though, the heavy-REE (Gd-Lu) for the felsic rock materials (e.g., JG-1a, JG-2, JR-1 and JR-2) showed large discrepancies compared with the compiled values, other elements are in good agreement. This can be explained due to the erroneous measurement of compiled values which may be attributed to incomplete dissolution of the rock materials for solution techniques.

Photoinduced dissociation of electrospray-generated ions in an ion trap/time-of-flight mass spectrometer using a pulsed CO2 laser.

An ion trap/time-of-flight (IT/TOF) mass spectrometer was developed and applied to infrared multiphoton dissociation (IRMPD) studies of ions generated by electrospray ionization. A pulsed 10.6- micro m laser beam from a CO(2) laser was used for excitation of trapped ions. Results from IRMPD of peptide ions show that this method provides useful information related to the amino acid sequence of analyzed peptides. Comparative studies show that IRMPD spectra are similar to those obtained using a 266-nm UV laser beam for excitation. However, in contrast to multiple-pulse excitation required at 266 nm, the energy of a single laser pulse in IRMPD is sufficient to induce dissociation of peptide ions. The laser power is practically an exclusive parameter that must be controlled in order to obtain IRMPD spectra that will provide the optimal structural information. It is further demonstrated that the IRMPD IT/TOF technique has the potential to probe the structural features of larger ions that cannot be readily fragmented by collision-induced dissociation (CID). A multiply charged ion of equine cytochrome c is successfully fragmented in a single laser pulse experiment. The IRMPD IT/TOF technique is also shown to be a promising tool for studying dissociation kinetics of peptide and protein ions. Unlike other methods that usually monitor the dissociation ion kinetics in a dissociation time frame of greater than milliseconds, the IT/TOF can promptly detect all product ions generated by the dissociation process, and thus monitor the dissociation process of peptides and proteins in a sub-millisecond time frame. This instrument allows us to determine the dissociation rates of cytochrome c ions using high-energy photoexcitation. It is found that the charge state of the protein ion has a significant effect on dissociation kinetics, which is consistent with that found under low-energy excitation experiments. It is shown that the increase in energy of a laser pulse from 130 to 180 mJ changes the dissociation rate constant for the +12 ion from k = 2.4 x 10(3) x s(-1) to k = 7.3 x 10(4) x s(-1). The +8 ion following excitation at 130 mJ dissociates slower with a rate constant of k = 2.6 x 10(2) x s(-1). The rate difference observed is attributed to conformational differences among the ions with different charge states.

Cerebral blood flow restoration and reperfusion injury after ultraviolet laser-facilitated middle cerebral artery recanalization in rat thrombotic stroke.

A reversible model of focal thrombotic stroke was developed in the rat and examined for histological evidence of reperfusion injury after clinically relevant times of recanalization. The distal middle cerebral artery of 28 male Sprague-Dawley rats was occluded by 562-nm laser-driven photothrombosis for 0.5, 2, and 3 hours or permanently (each n=7) and was recanalized by 355-nm UV laser irradiation. Occlusive material was examined by transmission electron microscopy. Cortical cerebral blood flow was monitored by laser-Doppler flowmetry. Brain infarcts were examined histologically at 3 days. After occlusion, cortical cerebral blood flow was reduced to 33+/-4% of baseline for all groups and was restored to 82+/-9%, 75+/-3%, and 93+/-7% of baseline for the 0.5-, 2-, and 3-hour groups, respectively, following recanalization after 29+/-8, 38+/-20, and 70+/-33 minutes of UV laser irradiation. The thrombotic occlusion contained compactly aggregated platelets but no fibrin, with length (1.2 to 1.8 mm) proportional to the ischemic period. During recanalization, microchannels containing erythrocytes and scattered leukocytes and bordered by intact disaggregated platelets infiltrated the thrombus. Infarct volumes (mm3) at 3 days were 12+/-3 for the permanent case and 8+/-4, 24+/-3, and 30+/-9 for the 0.5-, 2-, and 3-hour cases, respectively, thus demonstrating reperfusion injury histologically in the latter 2 groups. No hemorrhage was seen. UV laser-facilitated dissolution of a conventionally refractory platelet thrombus provides a novel and effective method for restoring blood flow without hemorrhagic complications during thrombotic stroke. This was the first observation of histologically confirmed reperfusion injury in such a model.

In situ analysis of trace elements in quartz by using laser ablation inductively coupled plasma mass spectrometry

There are several benefits which would result from the development of an in situ analytical technique for ultra trace elemental analysis of quartz, including rapid screening of possible high-purity quartz resources, by eliminating the need to remove solid and liquid inclusions by expensive dressing techniques prior to chemical analysis of structural impurities. Information on the petrogenetic history of the quartz can also be obtained from the distribution of trace elements. The main purpose of this paper is to describe an analytical method for estimating the concentrations of structural bounded trace elements in quartz. A double focusing sector field inductively coupled plasma mass spectrometry (ICP-MS, Finnigan MAT model ELEMENT), with the CD-1 Guard Electrode and a 266-nm UV laser ablation system was used in the development of the method for in situ analysis of quartz. The following elements are included in the analytical protocol: Al, Ba, Be, Cr, Fe, Ge, K, Li, Mg, Mn, Pb, Rb, Sr, Th, Ti, U. Analyses were carried out in low mass resolution ( m/Δ m=300), except for Mg, Ti, Cr, Fe (medium mass resolution, MR, m/Δ m≈3500) and K (high mass resolution, HR, m/Δ m>8000). The isotope 29Si was used as an internal standard at low resolution, and 30Si at medium and high resolution. External calibration was done by using the international reference materials: NIST 612, NIST 614, NIST 616, NIST 1830 from the National Institute of Standards and Technology (NIST), BCS 313/1 from the Bureau of Analysed Samples (BAS), the rhyolite RGM-1 reference sample from the United States Geological Survey (USGS), Reston and the certified reference material “pure Substance No. 1” silicon dioxide SiO 2 from the Federal Institute for Material Research and Testing, Berlin, Germany (BAM). Because of the absence of an SiO 2 blank, the BAM no. 1 SiO 2 was used for the estimation of detection limits. Detection limits for most of the elements are between 0.2 and 0.01 μg g −1. Analysis time and laser spot size were adjusted so that the raster did not exceed 300×300 μm on a 200-μm-thick section. New data for the international reference materials BCS 313/1 (BAS) and NIST 1830 and the standards BR-K1 and BR-FR2 are reported. To improve the lower limit of quantification and analytical uncertainty at low concentrations, it is important to have calibration curves with well defined intercepts. This can be achieved by the use of certified standards, with trace element concentrations lower than the BAM no.1 SiO 2 or a sample blank.

A mobile mass spectrometer for comprehensive on-line analysis of trace and bulk components of complex gas mixtures: parallel application of the laser-based ionization methods VUV single-photon ionization, resonant multiphoton ionization, and laser-induced electron impact ionization.

A newly developed compact and mobile time-of-flight mass spectrometer (TOFMS) for on-line analysis and monitoring of complex gas mixtures is presented. The instrument is designed for a (quasi-)simultaneous application of three ionization techniques that exhibit different ionization selectivities. The highly selective resonance-enhanced multiphoton ionization (REMPI) technique, using 266-nm UV laser pulses, is applied for selective and fragmentationless ionization of aromatic compounds at trace levels (parts-per-billion volume range). Mass spectra obtained using this technique show the chemical signature solely of monocyclic (benzene, phenols, etc.) and polycyclic (naphthalene, phenathrene, indol, etc.) aromatic species. Furthermore, the less selective but still fragmentationless single photon ionization (SPI) technique with 118-nm VUV laser pulses allows the ionization of compounds with an ionization potential below 10.5 eV. Mass spectra obtained using this technique show the profile of most organic compounds (aliphatic and aromatic species, like nonane, acetaldehyde, or pyrrol) and some inorganic compounds (e.g., ammonia, nitrogen monoxide). Finally, the nonselective ionization technique laser-induced electron-impact ionization (LEI) is applied. However, the sensitivity of the LEI technique is adjusted to be fairly low. Thus, the LEI signal in the mass spectra gives information on the inorganic bulk constituents of the sample (i.e., compounds such as water, oxygen, nitrogen, and carbon dioxide). Because the three ionization methods (REMPI, SPI, LEI) exhibit largely different ionization selectivities, the isolated application of each method alone solely provides specific mass spectrometric information about the sample composition. Special techniques have been developed and applied which allow the quasi-parallel use of all three ionization techniques for on-line monitoring purposes. Thus, a comprehensive characterization of complex samples is feasible jointly using the characteristic advantages of the three ionization techniques. Laboratory applications show results on rapid overview characterization of mineral oil-based fuels and coffee headspace. The first reported field applications include timely resolved on-line monitoring results on automobile exhausts and of waste incineration flue gas.

Aerosol matrix-assisted laser desorption ionization mass spectrometry

A new method of liquid sample introduction for a time-of-flight mass spectrometer (TOF-MS) has been developed by applying the method of matrix-assisted laser desorption ionization to aerosols. Analyte biomolecules are dissolved in a methanol solvent along with a UV-absorbing matrix and formed into an aerosol with a pneumatic nebulizer. The aerosol particles are dried in a heated skimmer tube before ionization by pulsed 355-nm UV laser radiation. Mass analysis is achieved in a linear TOF-MS. Results for the ionization of bovine insulin (5733.5 Mw) are reported.

Nanosecond laser flash photolysis of acridine in organic solvents

A laser flash photolysis set-up is described for nanosecond time resolved study of transient species. The system described uses 30 nsec, 355-nmuv laser pulse as the photolysing source. Laser flash photolysis of acridine in various organic solvents (polar, non-polar and hydroxylic) has been carried out. The quantum yields of intersystem crossing and C-radicals (in hydroxylic solvents) have been calculated from the transient absorption measurements. The quenching of the triplet state by chloranil is efficient in all the solvents and free radical ions are formed as products only in the polar solvents. Biphotonic ionisation of acridine occurs at high laser intensities and is more efficient in hydroxylic solvents compared to benzene or acetonitrile.