DUV Laser Research Articles

A design and comparative investigation of graded AlxGa1 − x N QB for W-Al0.58GaN/W-Al0.64–0.58 GaN DUV laser diode on AlN substrate

A design and comparative investigation of graded AlxGa1 − x N QB for W-Al0.58GaN/W-Al0.64–0.58 GaN DUV laser diode on AlN substrate

Thermal Characteristics of 266 nm DUV Laser Generated by BBO Crystal

Thermal Characteristics of 266 nm DUV Laser Generated by BBO Crystal

Kyropoulos growth of a 300 g SrB4O7 single crystal using a twin-type stirring blade

We report the successful Kyropoulos growth of a large strontium tetraborate (SrB4O7, SBO) single crystal that weighs more than 300 g. In order to grow the large and transparent crystal, a new twin-type stirring blade was used along with a 150 mm diameter crucible. The use of the stirring blade results in the production of the world’s largest SBO crystal with dimensions of 100 mm (a) ×30 mm (b) ×32 mm (c), a weight of 328.2 g, and wide transparency down to 130 nm. These results will then lead to the development of large SBO crystals as optical window materials for high-power DUV laser processing systems.

Threshold increase and lasing inhibition due to hexagonal-pyramid-shaped hillocks in AlGaN-based DUV laser diodes on single-crystal AlN substrate

The presence of hexagonal-pyramid-shaped hillocks (HPHs) in AlGaN epitaxial films affects device characteristics; this effect is significant in DUV laser diodes (LDs) on AlN substrates, where the presence of HPHs under the p-electrode increases the threshold current density and inhibits the lasing. In this study, we investigated the difference between the lasing characteristics of LDs with and without HPHs. It was found that in the presence of HPHs, the threshold excitation power density increased and the slope efficiency decreased by optical excitation. To investigate the cause of these phenomena, we performed structural, optical, and electrical analyses of the HPHs. Various imaging techniques were used to directly capture the characteristics of the HPHs. As a result, we concluded that HPHs cause the degradation of LD characteristics due to a combination of structural, optical, and electrical factors.

Deep-ultraviolet laser ablation sampling for proteomic analysis of tissue

Deep-ultraviolet laser ablation with a pulsed 193 nm ArF excimer laser was used to remove localized regions from tissue sections from which proteins were extracted for spatially resolved proteomic analysis by liquid chromatography tandem mass spectrometry (LC-MS/MS). The ability to capture intact proteins by ablation at 193 nm wavelength was verified by matrix-assisted laser desorption ionization (MALDI) of the protein standard bovine serum albumin (BSA), which showed that BSA was ablated and captured without fragmentation. A Bradford assay of the ablated and captured proteins indicated 90% efficiency for transfer of the intact protein at a laser fluence of 3 kJ/m2. Rat brain tissue sections mounted on quartz microscope slides and ablated in transmission mode yielded 2 μg protein per mm2 as quantified by the Bradford assay. Tissue areas ranging from 0.06 mm2 to 1 mm2 were ablated and the ejected material was collected for proteomic analysis. Extracted proteins were digested and the resulting peptides were analyzed by LC-MS/MS. The proteins extracted from the ablated areas were identified and the average number of identified proteins ranged from 85 in the 0.06 mm2 area to 2400 in the 1 mm2 area of a 50 μm thick tissue. In comparison to infrared laser ablation of equivalent sampled areas, both the protein mass and number of proteins identified using DUV laser ablation sampling were approximately four times larger.

High surface laser-induced damage threshold of SrB4O7 single crystals under 266-nm (DUV) laser irradiation.

Under 266-nm (deep ultraviolet, DUV) laser irradiation, an SrB4O7 (SBO) single crystal has been found to exhibit a surface laser-induced damage threshold (LIDT) of ∼ 16.4 J/cm2, which is higher than those of a synthetic silica glass (4.8 J/cm2) and a calcium fluoride (CaF2) crystal (11.4 J/cm2). By catalyst-referred etching (CARE), the LIDT of an SBO crystal can also be improved to around 24.1 J/cm2, which is 1.4 and 6.0 times higher compared to an unetched crystal and a silica glass, respectively. With high surface LIDTs, SBO single crystals can then be used as optical window materials for high-power DUV laser systems.

Investigation of Al- and N-implanted 4H–SiC applying visible and deep UV Raman scattering spectroscopy

Effects of aluminum (Al) and nitrogen (N) implantation performed at room and at elevated (500 °C) temperatures on epitaxial n-type 4H polytype silicon carbide as well as post-implantation annealing have been studied by Raman scattering spectroscopy. The amorphization of 4H–SiC is observed because of ion implantation effects. The Raman analysis showed that the recovery of the crystallinity increased with an increase in the annealing temperature. However, for samples implanted with high doses, the full crystal recovery was not complete even with annealing temperatures up to 1800 °C, and crystal defects were still present in the recrystallized layer, which was confirmed by transmission electron microscopy. Raman scattering spectra were collected at room temperature using a micro-Raman spectrometer. The visible (488 nm) and deep ultraviolet (266 nm) lasers were used as excitation sources. For the DUV laser, the optical penetration depth is less than the implanted layer thickness, and the area near the surface layer can be exactly probed. In contrast, the visible Raman spectrum shows bands characteristic of bulk 4H–SiC, which arise from the underlying non-implanted region. Based on the analysis of the longitudinal optical phonon–plasmon coupled mode, the electrical parameters for N2+ implanted samples were evaluated, where electron concentration n = 3.05 × 1018 cm−3 and mobility μ = 50 cm2/V s, respectively. The results are consistent with the parameters measured by the Hall method.

Formation of Al + (C 6 H 6 ) 13 : The Origin of Magic Number in Metal–Benzene Clusters Determined by the Nature of the Core

The identification of highly abundant, “magic” species in the mass spectra of clusters have proven to be valuable in nanoscience, leading to the discovery of new stable species such as fullerenes a...

An integrated instrument of DUV-IR photoionization mass spectrometry and spectroscopy for neutral clusters.

We have developed an integrated instrument combining deep ultraviolet laser ionization mass spectrometry (DUV-LIMS) and infrared multiphoton dissociation (IR-MPD) spectroscopy, abbreviated as DUV-IR. The 177.3 nm DUV laser (7 eV single-photon energy) has short pulse duration (15 ps) and appropriate pulse energy (∼20 µJ), which is found to be highly efficient for low-fragment photoionization of neutral metal clusters and molecules. A home-made cluster source is designed with an adjustable formation channel suitable for the generation of different cluster series. The well-aligned components of the reflection time-of-flight mass spectrometer, as well as the coaxial design of DUV laser and molecular beam, bring forth high sensitivity and high resolution of the DUV-LIMS. Taking these advantages, well-resolved neutral Vn (n = 1-43) and (Benzene)n (n = 1-25) clusters have been generated free of fragmentation. In addition to the generation and detection of neutral clusters, a fast-flow reaction tube is also designed downstream of the cluster source allowing to study their reactivity. In particular, a broad-range tunable IR laser (1.3-16 µm) is coupled with the DUV laser to attain IR-MPD spectroscopic analysis. This integrated system offers a general protocol to prepare various clusters to study their gas-phase reactivity and to determine their structures.

Deep Ultraviolet Laser Radiation Causes Brittle Fracture of Cα‐Cβ Bonds in Neurotransmitters

AbstractWe report here a photodissociation study of tyramine, tryptamine and histamine using the customized time‐of‐flight mass spectrometer (TOF‐MS) combined deep ultraviolet laser ionization. The cleavage of Cα‐Cβ bond, free of hydrogen atom transfer (HAT), is observed under the 177 nm DUV laser excitation, which is different from the HAT‐involved photodissociation by a 118 nm vacuum ultraviolet (VUV) laser. With aid of density function theory (DFT) calculations, we demonstrate the photochemical reaction mechanism of these neurotransmitter molecules with dependence on residual energies after photoionization and donor‐acceptor orbital interactions. This finding helps to enrich the understanding of structure chemistry of neurotransmitters. In particular, the brittle fracture of Cα‐Cβ bond initiated by the ultrafast DUV laser could stimulate research interest in designed synthesis of organic compounds.

Growth of high-quality transparent SrB4O7 single crystals with high degradation resistance for DUV laser application

We grew borate crystals, SrB4O7 (SBO), by the top-seeded solution growth (TSSG) method. High-quality transparent SBO single crystals were successfully obtained from the stoichiometric melt by a seed cooling technique. The optical properties of the SBO crystals, which showed wide transparency, high transmittance, and high resistance to optical damage compared with synthetic silica glass and CsLiB6O10 (CLBO) crystals, were evaluated. Our results reveal for the first time that the SBO crystals exhibit outstanding degradation resistance at a DUV wavelength of 266 nm.

脉冲LD泵浦电光调Q深紫外激光器

脉冲LD泵浦电光调Q深紫外激光器

Deep ultraviolet lasing from AlGaN multiple‐quantum‐well structures

AbstractWe report our research work on AlGaN/Al(Ga)N multiple‐quantum‐well (MQW) DUV laser structures. Two types of MQW structures, that is, AlxGa1‐xN/AlyGa1‐yN MQW (Sample A) and AlzGa1‐zN/AlN MQW (Sample B), were grown on sapphire substrates by Metal‐organic chemical vapour deposition. Optically pumped lasing at room temperature has been achieved from both structures. For Sample A, the main lasing emission wavelength is 288 nm along with some parasitic longer wavelength peaks. Numerical simulation results indicate that the optical confinement factor in Sample A is very low, less than 0.5%. This resulted in the high lasing threshold and short lasing lifetime of Sample A. The optical confinement factor of Sample B is greatly increased to more than 10%. This effectively improved the lasing performance of Sample B. Its lasing threshold is estimated to be 523 kW/cm2 and the lasing spectra peaked at around 281 nm. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Deep ultra violet and visible Raman spectroscopy studies of ion implanted 6H-SiC: Recrytallisation behaviour and thermal decomposition/thermal etching of the near surface region

The recystallisation behaviour and thermal decomposition of the near surface amorphised region of 6H-SiC have been investigated by Raman spectroscopy. 360keV ions of iodine and silver were implanted at room temperature into wafers of 6H-SiC resulting in the amorphisation of the near surface region. Vacuum annealing of the samples was performed at 1200°C for 5h and then sequentially from 1200 to 1600°C in steps of 100°C for 30h at each annealing temperature. Raman spectroscopy was performed using two laser wavelength excitation regimes, the 514nm laser (visible region) and the 244nm laser (deep ultraviolet region, DUV). Measurements in the visible region for samples annealed at 1200°C for 5h showed that the characteristic 6H-SiC peaks, namely, the Transverse Optical (TO) and Longitudinal Optical (LO) are similar to the virgin samples, albeit with lower intensity due to some retained defects upon recystallisation of the SiC surface region. The similarities between the virgin spectra and the annealed sample were due to the deep penetration of the 514nm laser into 6H-SiC resulting in the signal from the bulk undamaged 6H-SiC contributing to the overall spectra. However, DUV laser excitation, which only probes the near surface region, shows that after annealing the peaks are broader and asymmetrical compared to the virgin samples. DUV Raman spectra of samples annealed at 1600°C indicate that SiC has completely decomposed and the top surface layer is now covered by a carbon layer. However the deeper penetrating laser in the visible region showed that the extent of decomposition at 1600°C was greater for the silver implanted samples than for the iodine implanted samples.

Deep ultraviolet laser direct write for patterning sol-gel InGaZnO semiconducting micro/nanowires and improving field-effect mobility.

Deep-UV (DUV) laser was used to directly write indium-gallium-zinc-oxide (IGZO) precursor solution and form micro and nanoscale patterns. The directional DUV laser beam avoids the substrate heating and suppresses the diffraction effect. A IGZO precursor solution was also developed to fulfill the requirements for direct photopatterning and for achieving semi-conducting properties with thermal annealing at moderate temperature. The DUV-induced crosslinking of the starting material allows direct write of semi-conducting channels in thin-film transistors but also it improves the field-effect mobility and surface roughness. Material analysis has been carried out by XPS, FTIR, spectroscopic ellipsometry and AFM and the effect of DUV on the final material structure is discussed. The DUV irradiation step results in photolysis and a partial condensation of the inorganic network that freezes the sol-gel layer in a homogeneous distribution, lowering possibilities of thermally induced reorganization at the atomic scale. Laser irradiation allows high-resolution photopatterning and high-enough field-effect mobility, which enables the easy fabrication of oxide nanowires for applications in solar cell, display, flexible electronics, and biomedical sensors.

Theoretical analysis of strategies for improving p‐type conductivity in wurtzite III‐nitride devices for high‐power opto‐ and microelectronic applications

AbstractAchieving high p‐type conductivity is one of the most significant bottlenecks to the efficient operation of wurtzite III‐N based optoelectronic and microelectronic devices. Through judicious volumetric redistribution of fixed negative polarization charge, compositionally graded layers may be exploited to achieve nearly flat valence band profiles free from electrostatic barriers to hole injection into the active region. This may potentially ameliorate problems associated with poor p‐type conductivity and inefficient hole transport that complicates the design of DUV laser diodes and light emitting diodes. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

DUV Laser Sources for Semiconductor Inspection Tools

DUV Laser Sources for Semiconductor Inspection Tools

Long pulse duration of the UV laser with a multi-reflected cavity: Experiment and modeling

The long pulse operation of ultraviolet (UV) laser attributed to multi-reflection is presented on an acousto-optic (AO) Q-switched ultraviolet laser system blocking green light inside a cavity. The ultraviolet laser with the highest average power of 456 mW is obtained with 20 kHz repetition-rate. The numerical simulation of UV pulse broadening was studied using Gaussian curve approximation. The conclusion suggests that the short multi-reflected cavity and high incident pump power will be beneficial to alleviate the width broadening effect. The results, for the first time, would provide the technology for controlling the pulse width of an AO Q-switched DUV laser.

Rapid lifetime testing of fused silica for DUV laser applications

Lifetime testing of fused silica's absorption degradation upon 193 nm is shortened by enhancing the two-photon absorption (TPA) induced generation of E′ and NBOH defect centers per laser pulse. Increasing the irradiation fluence from typical marathon test values H < 1 mJ/cm 2 to H = 10 mJ/cm 2 gives a more efficient TPA process. In addition, the sample's temperature is lowered to −180 °C during irradiation yielding an increased breaking efficiency of weak Si–O bonds per pulse. A small sample length of 10 mm combined with the laser induced deflection (LID) technique for direct absorption measurements prevents microchannel (MC) formation, a common break-down criterion in marathon tests. For a UV grade fused silica sample (type III) the end of absorption degradation is found after about 1.2 * 10 7 laser pulses. Absorption measurements between 3 and 25 mJ/cm 2 before and after lifetime testing reveal that the laser induced absorption change decreases with decreasing fluence. The experimental results are in good agreement with a real marathon test at a fixed fluence.

Multi-reflected enhancement of fourth harmonic DUV laser generation at 266 nm

The stable compact operation in the deep ultraviolet laser at 266 nm is reported from a diode-end-pumped acoustic-optic Q-switched Nd:YVO4/KTP/BBO laser. Fourth harmonic is generated by employing multiple reflections of 532 nm light for taking full advantage of the green beam. An ultraviolet laser at 266 nm with average power of 388.5 mW is obtained with a repetition-rate of 20 kHz, a pulse width of about 59.80 ns, and the corresponding optical to optical conversion efficiency of 11.9% from green to UV. High conversion efficiency and a circular spot of 266 nm laser beam have been achieved in an unfocused beam arrangement.