Deep Ultraviolet Laser Research Articles

F 2 -laser digital etching of colloidal photonic crystals

We report on digital etching of silica colloidal photonic crystals by employing a pulsed deep-ultraviolet F2 laser at 157nm wavelength. When the laser fluence is above a microsphere-size-dependent threshold and within an appropriate fluence window, colloidal crystals can be etched in a digitized fashion, whereby a single microsphere layer can be removed upon exposure to a single laser pulse. Alternatively, single spheres or lines of spheres can be selectively ejected by patterning the laser beam. The results demonstrate a fast, noncontact, straightforward, and cost-effective approach for engineering extrinsic defects into colloidal photonic crystals.

Deep ultraviolet femtosecond laser tuning of fiber Bragg gratings

A deep ultraviolet femtosecond laser operating at wavelength 258 nm was demonstrated to be effective in trimming fiber Bragg gratings in telecommunication fibers. A smooth tunable resonance wavelength shift of up to 0.52nm has been observed, corresponding to a refractive index change of ∼5×10−4 after an accumulated laser fluence of 63.3kJ/cm2 at a single pulse fluence of 124 mJ/cm2. The ultrafast laser enhancement of ultraviolet photosensitivity response and modification of anisotropic index profile in silica fiber is a powerful technique to precise control of the performance of fiber Bragg grating devices for applications in optical filtering and polarization mode dispersion management.

High-gain harmonic generation free-electron laser with variable wavelength

The external seed of the high-gain harmonic generation (HGHG) free-electron laser (FEL) determines the wavelength of the output radiation. Therefore, the tunability of such a laser depends upon the tunability of the seed. In this paper, we present and discuss an alternative scheme for the tunable HGHG FEL wherein the seed's wavelength is fixed and the variations in the wavelength of radiation are achieved by tuning the accelerator. As an illustration, we apply our proposed scheme to the deep ultraviolet free electron laser (DUV FEL) at Brookhaven National Laboratory demonstrating the ability to attain about a +/-10% variation in the wavelength's tuning range.

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.

Experimental and clinical investigation of efficiency and ablation profiles of new solid-state deep-ultraviolet laser for vision correction

To investigate the efficiency and ablation profiles of a newly developed, all-solid-state laser platform. Experimental investigations performed at Katana Technologies GmbH, Kleinmachnow, Germany, and clinical study, at the Ophthalmology Clinic, University of Messina, Messina, Italy. Experimental studies were performed on poly(methyl methacrylate) (PMMA) and in porcine eyes using an all-solid-state, Q-switched, frequency-shifted laser (LaserSoft, Katana Technologies GmbH) with a Gaussian spot with a diameter of 0.2 mm in the target plane, a peak fluence of 350 mJ/cm2, and a repetition rate of 1 kHz. The ablation profiles were determined using a profile meter (MicroProf, Fries Research and Technology GmbH), corneal topography was analyzed with a TMS 2N (Tomey Inc.), and corneal thickness was measured with an ultrasound pachymeter (DGH Technology). In the clinical study, 9 human eyes were treated with photorefractive keratectomy. The mean outcome measures were uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), corneal topography, and corneal transparency. The follow-up was 1 month for all eyes and 3 months for 4 eyes. Safety, efficacy, and predictability were evaluated. Smooth profiles were found in the PMMA and the porcine eyes. The topographic maps showed central steepening after the hyperopic ablation and slight central flattening of the surface after the myopic treatment. No eye lost lines of BSCVA; the UCVA improved in all eyes. All eyes were within +/-1.00 diopter (D) of emmetropia, and 89% were within +/-0.50 D. The efficacy of the ablation was good, with the profile meter results confirmed by the topographic measurements.

Trimming phase and birefringence errors in planar lightwave circuits with deep ultraviolet femtosecond laser

A deep ultraviolet femtosecond laser was employed to trim phase and birefringence errors in silica planar lightwave circuits. A permanent refractive index change of ∼3.8×10−4 and a birefringence change of 1.0×10−4 were induced in hydrogen-free Mach-Zehnder planar waveguide circuits. The ultrafast laser enhances the ultraviolet photosensitivity response in silica waveguides by two orders of magnitude greater than that of a nanosecond 248 nm KrF excimer laser.

Growth and annealing conditions of high Al-content p-type AlGaN for deep-UV LEDs

We report on growth and annealing conditions for high Al-content p-type AlGaN that is required to achieve deep-ultraviolet (UV) light-emitting diodes (LEDs) or laser diodes (LDs). Mg-doped AlGaN epilayers with the Al-contents between 0 and 40% were grown by low-pressure (LP) metalorganic chemical vapor deposition (MOCVD). We found that the suitable annealing temperature for p-Al0.22Ga0.78N is around 900 °C, which is approximately 50 °C higher than that for p-GaN. We also demonstrated that the use of a lower V/III ratio and a higher growth temperature are preferable for the growth of high Al-content p-AlGaN, in comparison with the case of p-GaN. By controlling the growth and annealing conditions, we have achieved hole concentrations as high as 2.0 × 1018 cm–3 for Mg-doped AlGaN with an Al-content of 32% as determined by Hall effect measurement. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The Shanghai high-gain harmonic generation DUV free-electron laser

The Shanghai deep ultraviolet free-electron laser source (SDUV-FEL) is an HGHG FEL facility designed for generating coherent output with wavelength down to 88 nm. The design and the relevant R&D of this HGHG FEL source have been under way since 2000. Currently, a 150 MeV S-band electron injector is under construction as the first linac section to produce a high brightness beam. The design study and the present R&D status of the SDUV-FEL have been presented in this paper.

The Shanghai high-gain harmonic generation DUV free-electron laser

The Shanghai deep ultraviolet free-electron laser source (SDUV-FEL) is an HGHG FEL facility designed for generating coherent output with wavelength down to 88 nm. The design and the relevant R&D of this HGHG FEL source have been under way since 2000. Currently, a 150 MeV S-band electron injector is under construction as the first linac section to produce a high brightness beam. The design study and the present R&D status of the SDUV-FEL have been presented in this paper.

Simultaneous determinations of U-Pb age and REE abundances for zircons using ArF excimer laser ablation-ICPMS

Using a laser ablation-inductively coupled plasma mass spectrometer (LA-ICPMS), U-Pb age and rare earth element (REE) abundances have been determined simultaneously from a single 20 μm ablation pit of zircon. The laser ablation system utilizing 193 nm wave-length ArF excimer laser produces stable and reproducible signal intensities resulted in good precisions on measurements of element concentrations and isotopic ratios. Because of the higher energy density of the deep ultra-violet laser beam, ablation fractionation between Pb and U were reduced even with the prolonged ablation, and thus accuracy of Pb-U age was improved significantly. A chicane-type ion lens system was applied to a quadrupole-based ICPMS instrument. With the chicane ion lens, higher elemental sensitivity (4 times for light mass range and 3 times for mid to heavy mass range) and lower white background (<5 cps for light to mid mass range and <2 cps for heavy mass range) were achieved. This further improved analytical precisions for low concentration elements in samples. The 238U-206Pb ages for Nancy standard zircon (Nancy 91500), SHRIMP calibration standard zircon (SL13) and Antarctic zircon (PMA7) obtained in this study were 1064 ± 24 Ma, 569 ± 78 Ma and 2438 ± 101 Ma (2-sigma), respectively. Relative age differences from previous reports were 0.2%, 0.4% and 3.2% respectively, demonstrative of high reliability of the method. The REE abundances in zircon samples were calibrated using a NIST 610 glass standard reference material. The resulting REE abundance data for zircons (Nancy 91500 and SL13) show good agreement with those for literature values within the analytical precision of ∼20%. The matrix effect that may occur between the synthetic glass standard and zircon crystals is obviously smaller than the precision and thus negligible for this precision levels. The data presented here demonstrate clearly that the combination of ArF excimer laser and ICPMS equipped with the chicane ion lens has a potential to become a significant tool for zircon geochemistry.

Analysis of serotonin release from single neuron soma using capillary electrophoresis and laser-induced fluorescence with a pulsed deep-UV NeCu laser.

The use of capillary electrophoresis (CE) with laser-induced fluorescence excited by ultraviolet (UV) lasers in the range 200-300 nm has been restricted by the available wavelengths and expense of UV lasers. The integration of a NeCu deep UV laser operating at 248.6 nm with a single channel CE system with post-column sheath flow detection allows detection limits for serotonin and tryptophan of 3.9x10(-8) M and 4.5x10(-8) M respectively. Single cell analysis of serotonergic metacerebral cells from the sea slug Aplysia californica yields a value of 800+/-85 fmol of serotonin in each cell soma. For the first time, serotonin is directly detected in electrically stimulated release from single metacerebral cell soma, with approximately 4% of the serotonin contained in the soma released from a semi-intact preparation with a 2 min electrical stimulation.

A quasi-continuous-wave deep ultraviolet laser source

We have developed a quasi-CW, deep ultraviolet source producing >250 mW of 205-nm radiation. The source consists of a 100-MHz, mode-locked, 15-W, 1047-nm master-oscillator/power-amplifier, a synchronously pumped optical parametric oscillator, and three nonlinear conversion stages.

Reactive electron beam evaporation of gadolinium oxide optical thin films for ultraviolet and deep ultraviolet laser wavelengths

Availability of ultraviolet optical thin film materials, especially high index refractory oxides that transmit down to deep ultraviolet (approx. 0.2 μm) is very much limited. The present article discusses some of the research optimization studies on gadolinium oxide (Gd 2O 3), a novel lanthanide sesquioxide material, for such challenging spectral requirements. Optical and topographical properties of single layer films have been studied using phase modulated spectroscopic ellipsometry, spectrophotometry and multimode atomic force microscopy. Films deposited at lower substrate temperatures have shown higher band gaps and higher substrate temperatures yielded higher refractive indices. Multilayer high reflection filters have been developed for ultraviolet laser wavelengths such as ArF (193 nm), KrCl (222 nm), KrF (248 nm) and Nd-Yag-III (355 nm), using this material at lower substrate temperature conditions and successfully tested for their performances.

First SASE and seeded FEL lasing of the NSLS DUV FEL at 266 and 400 nm

The Deep Ultra-Violet Free Electron Laser (DUVFEL) at the National Synchrotron Light Source consists of a 5MeV photoinjector, a 200MeV S-band linear accelerator, a four-magnet chicane compressor and a 10m wiggler with a 3.9cm period. The commissioning of the SDL accelerator was completed recently and it is routinely producing a high-quality electron beam with a peak current of ∼400A and a normalised emittance of 3–4mmmrad. The first SASE lasing of the DUV FEL has been demonstrated at both 266 and 400nm. The gain length of the SASE experiments was measured to be 66cm in both cases and up to 20nJ per pulse was obtained. A laser seeded FEL at 266nm is in the very early stages of commissioning and amplification of the laser seed has been observed. The goal of the seeded laser FEL is to saturate the FEL and thereby generate sufficient third harmonic at 89nm for experimental applications. Here we report the observation and measurements of SASE at 400 and 266nm and the first results of seeded FEL.

Efficient compact watt-level deep-ultraviolet laser generated from a multi-kHz Q-switched diode-pumped solid-state laser system

Stable high-power operation in the deep ultraviolet is achieved from a multi-kHz diode-pumped multi-longitudinal-mode Q-switched Nd:YAG laser by fourth harmonic generation in an external resonant cavity and by fifth harmonic generation using sum-frequency mixing of the fourth harmonic and the residual fundamental in a β-BBO crystal. Over 2.1 W of 266 nm radiation and 540 mW of 213 nm radiation were generated from a fundamental power of 7 W of 1064 nm light at 5 kHz. The overall conversion efficiency from IR to deep ultraviolet at 213 nm is larger than 7.5%.

Master Recording for High-Density Disk Using 248 nm Laser Beam Recorder

A deep ultra-violet (UV) laser beam recorder (LBR) with 248 nm wavelength was developed to realize a high-density disk. The characteristics of the LBR are the wavelength and the multifunctional design. Among the possible laser wavelengths, 248 nm is the shortest wavelength applicable with Novolac photoresist, and the LBR has both modulation and deflection functions to support various formats flexibly. It was confirmed that the LBR performance was such that a groove of even 0.26 µm track pitch could be recorded, and the shape was observed with a scanning electron microscope (SEM). The disk with a groove of 0.32 µm track pitch recorded by the LBR had a practical deviation in the tracking error signal, and the addressed disk with phase-change material and a 0.1-mm-thick cover layer showed the stable reproduction of the address and a practical jitter at the equivalent density for achieving 25 GB capacity at 120 mm in diameter, on the condition of having a pick-up head with a wavelength of 400 nm and an NA of 0.85.

Hollow cathode ion lasers for deep ultraviolet Raman spectroscopy and fluorescence imaging

This article describes the development of hollow cathode ion lasers and their use in constructing an ultraviolet micro-Raman spectrograph with native fluorescence imaging capability. Excitation at 224.3 nm is provided by a helium–silver hollow cathode metal ion laser and at 248.6 nm by a neon–copper hollow cathode metal ion laser. Refractive microscope objectives focus chopped continuous wave laser light on a sample and collect 180° scattered photons. Imaging is accomplished by broadband visible illumination and by deep ultraviolet laser induced excitation of visible wavelength native fluorescence in untagged micro-organisms. This makes possible a detection strategy employing rapid imaging with laser excitation to locate regions of native fluorescence activity, followed by deep ultraviolet resonance Raman spectroscopy of the identified fluorescent sites. We have employed this probe for in situ detection of micro-organisms on mineral and soil substrates. We present here the deep ultraviolet resonance Raman spectra for the gram negative iron reducing bacterium Shewanella oneidensis obtained while the micro-organism remains in situ on the unpolished surface of the mineral calcite and in a Mars soil analog, JSC1. In the current configuration the in situ mineral surface limit of detection for fluorescence is one organism in 2×104 μm2 field of view and of order 20–30 micro-organisms for Raman spectra. For the Mars soil sample analog fluorescent target selection gives an effective ultraviolet resonance Raman spectral detection limit of 6×104cells/gm or ∼60 ppb.

UV Raman Spectroscopy of Single-Walled Carbon Nanotubes

Deep UV Raman spectroscopy is emerging as a useful tool for the characterization of carbon materials that has many advantages over visible Raman spectroscopy. However, because of resonance enhancement and other effects, UV Raman spectra are often different from visible Raman spectra. UV Raman spectra have not been reported for even some of the most widely known carbon materials. We report Raman spectra of single-walled carbon nanotubes (SWNTs) collected with deep ultraviolet (4.8 eV) laser excitation. There are significant differences between the deep UV and the visible Raman spectrum of SWNTs for the graphitic “G” modes and “disorder-induced” “D” modes, which are common to a wide range of forms of carbon. Furthermore, only semiconducting tubes are observed in the UV Raman spectrum, which is not consistent with an expected resonance enhancement of the scattering from metallic tubes at 4.8 eV.

Laser shaping of photonic materials: deep-ultraviolet and ultrafast lasers

Optical materials are especially challenging to process with conventional lasers simply because of their high transparency. We are exploiting two extremes in laser technology — ultrafast lasers and very short wavelength F 2 lasers — to microsculpt surfaces and to control refractive index in transparent glasses. These lasers drive fundamentally different interactions, many-photon and ‘big’ photon, respectively, that offer distinct advantages and limitations for shaping photonic devices in fused silica. Comparisons of surface morphology, shock-induced microcracking, resolution, and photosensitivity responses are presented.

Room-temperature deep-ultraviolet-stimulated emission from AlxGa1−xN thin films grown on sapphire

Room-temperature deep-ultraviolet-stimulated emission (SE) has been observed from optically pumped metalorganic chemical vapor deposition grown AlxGa1−xN thin films. SE has been observed for Al concentrations as high as x=0.26, with a resultant SE wavelength as low as 328 nm at room temperature. The results obtained for the AlxGa1−xN layers are compared with InxGa1−xN layers of comparable alloy concentration and GaN reference layers. The incorporation of Al into GaN is shown to result in AlxGa1−xN layers with similar high excitation-density emission behavior as GaN, in contrast to InxGa1−xN layers, which exhibit markedly different SE behavior. The observation of room-temperature SE from AlxGa1−xN layers of significant Al concentration illustrates the suitability of AlxGa1−xN based structures, not only for use in deep-ultraviolet detectors, but also as a potential source of deep-ultraviolet laser radiation.