Deep UV Laser Research Articles

Processing of membrane protein crystal using ultraviolet laser irradiation

We demonstrated the processing of a membrane protein crystal, using a pulsed UV laser soft ablation (PULSA) technique. Irradiation with deep-UV laser pulses at a wavelength of 193 nm successfully processed not only single crystals of the membrane transporter protein AcrB but also nylon loops and cryoprotectants at a cryogenic temperature. Nonprocessed parts of the crystals exhibited no signs of crack or denaturation after the laser exposure. The trimmed crystals were found to be of high resolution for X-ray diffraction data collection. The results described here indicate that PULSA processing is an effective tool for membrane protein crystals, as well as for soluble protein crystals.

Backward quasi-phase-matched second-harmonic generation in submicrometer periodically poled flux-grown KTiOPO4

A 1mm thick flux-grown KTiOPO4 sample was poled with a 720nm domain period by employing deep-UV laser lithography, chemical patterning, and electric field poling. An atomic force microscope was used to characterize the periodic domain structure. The sample was used to demonstrate sixth and seventh order quasi-phase-matched backward second-harmonic generation.

Diamond microstrip detector for deep UV imaging

CVD diamond detectors with metal diamond metal (MDM) microstrip structures have been constructed and characterized for image sensor and large area applications. These sensors are suitable for UV and soft X-ray detection. The device photoelectrical characterization under deep UV ( λ=193 nm) laser pulses has been performed both on the nucleation and growth sides of a diamond slab, by varying bias voltage, contacts interspacing and light intensity. Such a characterization was also performed on a laser-smoothed part of the growth side. Reflecting the true electronic quality, largely different photocurrent peak shapes were detected on the untreated and laser-treated parts of the growth side, as well as on the nucleation side. Pulse amplitude and duration appear to decrease according to the different defect density value, which turns out to be larger on the laser-treated growth side of the diamond slab. Independent of pulsed illumination intensity, a linear photoresponse increase with the applied electric field is found in the range 10 1–10 4 V/cm. Depending on the defect density value, the photocurrent versus pulse energy changes according to a different power law, the linear dependence extending into a wider pulse energy range when larger defect densities are involved. Such a characteristics is also a figure of the wide signal dynamics. The sensor uniformity has been also tested both on as grown and laser-treated surface, as well as on the nucleation side surface where a linear signal increase has been found by adding adjacent strips connected in parallel. These results suggest the suitability of the sensor for image acquisition.

Deep UV Laser-Induced Fluorescence Detection of Unlabeled Drugs and Proteins in Microchip Electrophoresis

Deep UV fluorescence detection at 266-nm excitation wavelength has been realized for sensitive detection in microchip electrophoresis. For this purpose, an epifluorescence setup was developed enabling the coupling of a deep UV laser into a commercial fluorescence microscope. Deep UV laser excitation utilizing a frequency quadrupled pulsed laser operating at 266 nm shows an impressive performance for native fluorescence detection of various compounds in fused-silica microfluidic devices. Aromatic low molecular weight compounds such as serotonin, propranolol, a diol, and tryptophan could be detected at low-micromolar concentrations. Deep UV fluorescence detection was also successfully employed for the detection of unlabeled basic proteins. For this purpose, fused-silica chips dynamically coated with hydroxypropylmethyl cellulose were employed to suppress analyte adsorption. Utilizing fused-silica chips permanently coated with poly(vinyl alcohol), it was also possible to separate and detect egg white chicken proteins. These data show that deep UV fluorescence detection significantly widens the application range of fluorescence detection in chip-based analysis techniques.

Degradation Behavior and Damage Mechanisms of CCD Image Sensor With Deep-UV Laser Radiation

As the deep-ultraviolet (DUV) laser technology continues to mature, an increasing number of industrial applications is shifting to intense DUV radiation sources. This trend necessitates the development of DUV sensitive charge-coupled device (CCD) cameras to provide imaging capability for process control and inspection purposes. In this paper, we examine the effects of DUV laser radiation on CCD image sensor characteristics and the mechanisms responsible for DUV laser damage in CCDs. When samples of thinned front-illuminated linescan CCD sensors are exposed to F/sub 2/(/spl lambda/=157 nm) excimer laser radiation, fluctuation in the extrinsic quantum efficiency (QE) and a substantial upsurge in the dark current density are observed as a function of exposure dose. The visible QE, dark current, and charge conversion efficiency (CCE) are also permanently altered by the DUV irradiation. These instabilities can be attributed to a variety of UV-induced effects that modify the optical and electrical properties of the SiO/sub 2/ layer and Si-SiO/sub 2/ interface, resulting in temporary and permanent shifts in CCD performance. Optimization of the overlying oxide thickness and the Si-SiO/sub 2/ interface quality are necessary in order to realize CCD sensors with the desired performance, radiation tolerance and stability at DUV wavelengths.

Optical studies on GaN-based spintronics materials

Structural properties of GaN layers doped with magnetic impurities (Mn, Cr) were investigatedby Raman scattering. In the case of Mn-doping, an impurity mode was observed at around585 cm−1 with concentrations of Mn up to 1–2%. This mode was assigned to a local vibrational modeof Mn substituting the Ga site, and interpreted as spectral evidence of a uniform solidsolution in the samples. For Cr-doping, good crystalline quality was also confirmed up to[Cr] = 3–5%. Cr is more miscible in GaN than Mn. Resonance enhancement of LO phonon signal wasobserved in GaCrN layers when excited by a deep UV laser at 266 nm (4.7 eV). Thisindicates generation of photo-carriers.

Raman studies on spintronics materials based on wide bandgap semiconductors

Structural properties of GaN and ZnO layers doped with magnetic impurities wereinvestigated by Raman scattering. Long-range lattice ordering and local atomicarrangement around magnetic impurities were analysed, and their solubility limit wasconsidered.For this study, GaN layers doped with Mn and Cr, and ZnO layers doped with Coand V were prepared by molecular beam epitaxy and pulsed laser deposition,respectively. ZnO layers codoped with Ga and N were also studied for the purposeof p-type activation. These samples were observed using a Raman microprobeusing visible and deep UV lasers for excitation. The main results are as follows:In Ga1−xMnxN layers, a uniform solid solution was formed for Mn concentration up tox = 1–2%. An impuritymode was observed at 585 cm−1 and assigned to a local vibrational mode of Mn substituting the Ga site. Athigher Mn concentrations, rapid deterioration in lattice ordering occurred.Ga1−xCrxN layers showed goodlattice ordering up to x = 3–5%. The samples showed resonance enhancement of LO-phonon signals when excited by aUV laser at 266 nm (4.7 eV). This indicates the photo-injection of free carriers to a dilutedmagnetic semiconductor.ZnO layers codoped with Ga and N showed many impurity modes due to host lattice defects. A strongsignal at 580 cm−1 showed a characteristic broadening at high concentrations of N and Ga.This suggested the formation of complex centres with N or related defects.Zn1−xCoxO and Zn1−xVxO layers formed uniform solid solutions up to , but precipitation of the secondary phase was observed at . These samples presented common defect modes as observed in codoped samples. Ourresult suggests that the impurity modes in ZnO-based materials can be used as asensitive probe of host lattice defects induced by the impurity incorporation process.

펨토초레이저와 자기조립박막을 이용한 나노스케일 패터닝

Standard positive photoresist techniques were adapted to generate nano-scale patterns of gold substrate using self-assembled monolayers (SAMs) and femtosecond laser. SAMs formed by the adsorption of alkanethiols onto gold substrate are employed as very thin photoresists, Alkanethiolates formed by the adsorption of alkanethiols are oxidized on exposure to UV light in the presence of air to alkylsulfonates. Specifically, it is known that deep UV light of wavelength less than 200nm is necessary for oxidation to occur. In this study, ultrafast laser of wavelength 800nm and pulse width 200fs is applied for photolithography. Results show that ultrafast laser of visible range wavelength can replace deep UV laser source for photo patterning using thin organic films. Femtosecond laser coupled near-field scanning optical microscopy facilitates not only the patterning of surface chemical structure, but also the creation of three-dimensional nano-scale structures by combination with suitable etching methods.

Sub-micron scale patterning using femtosecond laser and self-assembled monolayers interaction

Standard positive photoresist techniques were adapted to generate sub-micron scale patterns of gold substrate using self-assembled monolayers (SAMs) and femtosecond laser. Self-assembled monolayers formed by the adsorption of alkanethiols onto gold substrate are employed as very thin photoresists. The process underlying photopatterning of SAMs on gold is well-known at the phenomenological level. Alkanethiolates formed by the adsorption of alkanethiols are oxidized on exposure to UV light in the presence of air to alkylsulfonates. Specifically, it is known that deep UV light of wavelength less than 200 nm is necessary for oxidation to occur. In this study, solid state femtosecond laser of wavelength 800 nm is applied for photolithography. The results show that ultrafast laser of near infrared (NIR) range wavelength can replace deep UV laser source for photopatterning using thin organic films. The essential basis of our approach is the photochemical excitation of specific reactions in a particular functional group (in this case a thiolate sulfur atom) distributed with monolayer coverage on a solid surface. Femtosecond laser photolithography could be applied to fabricate the patterning of surface chemical structure and the creation of three-dimensional nanostructures by combination with suitable etching methods.

High-Density Read-Only-Memory Disc Mastering Using Direct-Focus Laser Beam Recorder

The authors have developed a novel laser beam mastering apparatus using a deep-UV (DUV) laser for a high-density optical disc. A direct focusing mechanism, where the recording beam itself is also used for focusing, is applied in the laser beam recorder (LBR). The mechanism solves the focus depth issue and provides stable focusing. The evaluation results for the 23.3-Gbytes-capacity read-only-memory (ROM) disc revealed that uniform recording can be realized. Jitter variations in the tangential and radial directions were suppressed to less than 0.2% and 0.07%, respectively. A low residual tracking error signal was also attained. The measurement results for the 25-Gbyte-capacity disc show reasonable jitter not only for a resist/glass disc, but also for an injection-molded disc. The tilt margin of the disc confirmed that the disc was practical for application in the market. Furthermore, the evaluation of the 27 GByte disc indicated the possibility of higher density ROM disc mastering.

Manufacture of 27 GB Read-Only-Memory Disc Using Deep-UV Beam Recorder with Two-Dimensional Optical Compensation

A novel mastering method using a deep-UV laser beam recorder (LBR) with two-dimensional optical compensation has been proposed. Using this technique, uniform fine pits can be created. The result reveals that a 27 GB read-only-memory (ROM) disc can be realized. The bottom jitter with a limit equalizer was 7.5%.

Photosensitization of standard fibers with deep uv laser radiation

A strong and permanent ultraviolet photosensitivity enhancement was locked into standard optical fiber pre-treated with above-bandgap 157-nm F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -laser radiation. Below-bandgap 248-nm irradiation of the pre-treated fiber yielded fiber Bragg gratings (FBGs) with an index contrast of 6.5 × 10/sup -4/, a value four-fold larger than that available in 16% Ge-doped photosensitive fiber. The F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -laser photosensitivity locking was 300 times more effective than with KrF-laser pre-treatment in terms of the accumulated fluence required to lock in a similar refractive index change. Accelerated FBG aging tests equivalent to 25 years at 70°C revealed a less than 2% reflectivity decay in both 157- and 248-nm pre-treated fibers, which is sufficient to eliminate the postannealing step typically required in hydrogen-loaded fibers. The large photosensitization and the superior thermal stability of both 248- and 157-nm pre-treated fibers are associated with a new Si-H bond absorption feature at 1387 nm, which appears only during the FBG formation step.

Deep UV laser induced fluorescence in fluoride thin films

Fluorescence experiments have been performed to study the interaction of 193-nm laser radiation with dielectric thin films of LaF3, AlF3, and MgF2. Spectral- and time-resolved measurements reveal the presence of cerium in LaF3 and the influence of hydrocarbons in MgF2 and LaF3. Virtually no fluorescence response is observable in the case of AlF3. Supplementary measurements on multilayer stacks confirm the contribution of hydrocarbon and cerium emission in high-reflective UV mirrors upon ArF excimer laser irradiation. Energy density dependent measurements indicate a linear absorption process as the origin of UV laser induced fluorescence in LaF3. Luminescence calculations are applied as a helpful tool in order to account for interference effects that are inherently to be found in the multilayer emission spectra.

Stimulated Emission at 258 nm in AlN/AlGaN Quantum Wells Grown on Bulk AlN Substrates

AbstractWe report on observation of stimulated emission at 258 nm in AlN/AlGaN multiple quantum wells. The structures were grown over Al-face single crystal bulk AlN substrates. AlN/AlGaN structures with 50% of Al in the well material were grown using low-pressure metalorganic chemical vapour deposition. Characterization by using X-ray, AFM, SEM, and photoluminescence techniques indicated high structural quality of the structures. The stimulated emission was measured using the variable stripe length method under excitation by 4-ns-long pulses of the fifth harmonic of Nd:YAG laser radiation at 213 nm (5.82 eV). The stimulated emission exhibited a characteristic superlinear dependence of emission intensity on the pump intensity as well as an exponential increase of the sample-edge emission intensity with increasing stripe length up to ∼430 μm and the intensity saturation beyond this range. The observation of stimulated emission at 258 nm is very promising for the future development of III-nitride-based deep-UV laser diodes on bulk AlN substrates.

Deep UV laser induced luminescence in oxide thin films

Time-resolved luminescence experiments have been set up in order to study the interaction of 193-nm laser radiation with dielectric thin films. At room temperature, Al2O3 coatings show photoluminescence upon ArF excimer laser irradiation, with significant intensity contributions besides the known substrate emission. Time- and energy-resolved measurements indicate the presence of oxygen-defect centers in Al2O3 coatings, which suggests a strong single-photon interaction at 193 nm by F+ and F center absorption. Measurements on highly reflective thin-film stacks, consisting of quarter-wave Al2O3 and SiO2 layers, indicate similar UV excitations, mainly from color centers of Al2O3.

Development of a combined confocal and scanning near‐field Raman microscope for deep UV laser excitation

AbstractWe describe the development of a combined confocal and scanning near‐field Raman microscope for operation at deep UV wavelengths. This instrument is based upon a commercially available Raman microscope and enables far‐field and near‐field Raman spectra to be acquired from the same location on a sample. The application of the confocal and scanning near‐field microscopes was demonstrated by studies of CVD diamond films. Copyright © 2002 John Wiley &amp; Sons, Ltd.

High-speed diamond photoconductors: a solution for high rep-rate deep-UV laser applications

Beam monitoring of excimer lasers operating at high powers in the deep ultra-violet (DUV) is becoming increasingly important, due to the rapid proliferation of these systems in micromachining, photolithography, and other areas of industrial interest. This task requires radiation-hard detectors able to operate effectively for extended periods at high laser rep-rates. DUV-visible-blind photoconductors can be fabricated on polycrystalline CVD diamond, a material that is intrinsically radiation-hard and visible-blind. However, the performance of detectors fabricated on as-grown material is insufficient to meet the requirements of many excimer laser applications. In this paper, we show that sequentially applied post-growth treatments can progressively change both the gain and speed of these devices. Charge-sensitive deep-level transient spectroscopy (Q-DLTS) and transient photoconductivity (TPC) has been used to study the effect of these treatments on the defect structure of our thin-film diamond detector material. For the first time, we report the successful operation of a diamond photoconductive device with linear bias and fluence-response characteristics at more than 1 kHz at 193 nm.

All-solid-state, high-power, deep-UV laser system based on cascaded sum-frequency mixing in CsLiB_6O_10 crystals

We report on an efficient use of CsLiB6O10 (CLBO) crystals employed for an all-solid-state deep-UV laser system operated at 5 kHz. We obtained greater than 3 W of UV radiation around 242 nm by mixing the 349-nm third harmonic of a Nd:YLF laser with the tunable output from a Ti:sapphire laser in a CLBO crystal. This UV radiation was subsequently mixed with the residual 1047-nm output from the Nd:YLF laser in a second CLBO crystal. The system produced 1.5 W of deep-UV radiation at 196.3 nm, which is, to our knowledge, the highest deep-UV power below 200 nm generated in a nonlinear optical crystal. Additionally, the bandwidth of both outputs was estimated to be less than 200 MHz.

The control of B N and B C bonds in BCN films synthesized using pulsed laser deposition

A novel chemical bond transformation from BN to BC was observed in BCN films synthesized using pulsed laser deposition (PLD). BCN film prepared by using green laser (λ=532 nm) induced two IR absorption at 1370 and 800 cm−1. This film was dominated by amorphous carbon phase and sp2 hybridized BN bonds. BCN film deposited using an ultraviolet (UV) laser (λ=266 nm ) induced an addition infrared (IR) absorption at 1250 cm−1. As we deposit BCN film by deep-UV laser (λ=213 nm), the absorption at 1370 and 800 cm−1 disappeared while the absorption at 1250 cm−1 remained. According to X-ray photoelectron spectroscopy (XPS), BC bonds with a carbon rich composition were formed. The formation of BC bonds in BCN films was also sensitive to deposition gas pressure and substrate temperature. Reactive carbon and boron species were needed to enable BC bonds that hybridized the carbon and the BN phases. A low substrate temperature was required to avoid competition with sp2 hybridized pure BN and pure carbon bonds.

Solid Rare Gas Isolated Ionic Exciplexes for Deep UV and VUV Lasers

Emissions of ionic alkalihalide exciplexes (AX) + due to the B 2Σ→X 2Σ transitions of Cs 2+ F −, Cs 2+ Cl − and Rb 2+ F − are reported for CsF (196.5 nm), CsCl (220.1 nm) and RbF (136 nm) isolated in Ne and Ar matrices under e–beam excitation. The C 2Π →A 2Π transition could be only observed in the condensed phase (solid Ne) at 227 nm (CsF) and at 249.2 nm (CsCl). A higher emission efficiency of the ionic excimers in the condensed phase compared to gas phase is obtained. Apparently, a strong quenching of the B→X bands is observed at AX concentrations larger than 0.6%. These band lineshapes are explained and attributed to the transition from $$ B_{v' = 0} $$