XeF Excimer Laser Research Articles

Matrix-assisted laser desorption using a fast-atom bombardment ion source and a magnetic mass spectrometer.

A conventional fast-atom bombardment (FAB) ion source was used to achieve matrix-assisted laser desorption (MALD) in a high-mass, double-focusing, magnetic mass spectrometer. The pulsed ion signals generated by irradiation of a mixture of sample and matrix (2,5-dihydroxybenzoic acid) with either a XeF excimer laser (353 nm) or a nitrogen laser (337 nm) were recorded with a focal-plane detector. A resolution (full-width at half maximum) of 4500 was achieved at m/z 1347.7 (the peptide substance P), 2500 for CsI cluster ions at m/z 10,005.7, and 1250 for the isotope cluster of the small protein cytochrome c (horse) [M+H]+ = m/z 12,360 (average). Sensitivity is demonstrated with 11 fmol of substance P. A survey scan is taken to locate the m/z of the sample molecular ion. The segment that contains the sample can then be integrated for a longer time to produce a better signal-to-noise ratio. In addition to higher sensitivity and lower matrix interference, the advantage of MALD over FAB is the former's lower susceptibility to the presence of salts, and competition between hydrophobic and hydrophilic components of a mixture. This feature is demonstrated by the complete MALD spectrum of a crude partial tryptic digest of sperm-whale apomyoglobin, containing 24 peptides, representing the entire sequence of this protein.

Matrix‐assisted laser desorption ionization with a magnetic mass spectrometer

Matrix-assisted laser desorption ionization has been carried out with a high mass double-focusing magnetic mass spectrometer. The pulsed ion signal, generated by irradiation of the sample (substance P, ubiquitin, and cytochrome c) embedded in 2,5-dihydroxybenzoic acid with a XeF excimer laser (353 nm, 12 ns pulse, 10-160 Hz), was recorded with an integrating array detector. Good resolution of 2600 (full width at half maximum) and high sensitivity (a few pmol) were obtained. The loss of small neutral fragments was observed, supporting the notion that the peak broadening observed in the time-of-flight mass spectrometers commonly used for this ionization mode is due to such metastable decomposition.

Understanding the formation of the SRS Stokes spectrum in fused silica fibers

Spectral characteristics of stimulated Raman scattering (SRS) in optical fibers are examined in a regime (nanosecond pulses or longer) for which effects such a self-phase modulation, cross-phase modulation, and group velocity dispersion are negligible. An XeF excimer laser was used to pump a multimode fused silica UV optical fiber to observe SRS multiple-order Stokes generation. A theoretical model in which SRS is the only nonlinear effect induced was developed to simulate the SRS spectra of excimer laser pumped silica fibers. Good agreement has been achieved on spectral characteristics of SRS between the computer simulation and experimental results, which clarifies several puzzling features observed in experiment. The most important parameters to the evolution of SRS spectra in fibers were found to be the Raman gain curve, and the linewidth and temporal profile of the input pump.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Structure of polymer blends photo-cross-linked during the spinodal decomposition process

Anthracene-labeled polystyrene/poly(2-chlorostyrene) blends (PSA/P2CS) (40/60) are photo-cross-linked during the time evolution of the spinodal-decomposition process by utilizing the intermolecular photodimerization reaction between anthracene groups. Optical microscopy and dielectric measurements show that, upon irradiation with a XeF excimer laser, the ordered structures resulting from a temperature-jump from the one phase into the spinodal region were efficiently frozen. For a constant duration time of irradiation (5 min), the sizes of these ordered structures become larger as the blend was photo-cross-linked at a later time

Actinometry of an excimer laser with a ferrioxalate chemical actinometer.

Actinometry of intense UV lights from ArF, KrF and XeF excimer lasers has been studied with a ferrioxalate chemical actionometer. The relation between the number of photons per pulse (N) and the absorbance change per pulse (ΔA) at 510 nm is expressed by using a first-order function, N=a·ΔA-b. (a, b: numerical constants characterized by a laser-wavelength). The experimental errors in this method were 4.8, 5.2, and 1.6% for ArF, KrF and XeF excimer lasers, respectively. The results prove that the ferrioxalate chemical actinometer is satisfactorily usable as an actinometer for excimer lasers.

Repetitively pulsed operation of an injection-controlled high-power XeF(C to A) excimer laser

The operation at a 1-Hz repetition frequency of an injection-controlled electron-beam-pumped XeF(C to A) excimer laser system is reported. A compact, halogen-compatible, closed flow loop incorporating a transverse inline fan was used for gas circulation. In single-laser-shot operation, the timing between an electron beam and the injection dye laser was carefully adjusted to obtain an optimum laser pulse energy stability. An improved output-laser energy of 1.2 J per pulse with an intrinsic efficiency of 1.1% at 486.8 nm was achieved with a large-aperture unstable resonator. Interferograms taken during and after an electron-beam pump pulse to determine the minimum optical cavity recovery time of this device indicate that stable laser output energy performance at repetition rates of up to 25 Hz could be achieved with the present flow loop. >

Optimization of an injection-controlled excimer laser guided by analytical modeling

The application of an analytical model describing the injection control of pulsed laser systems is successfully demonstrated for the design of a scaled XeF(C to A) excimer laser system. Enhancements to an earlier version o the model which improve the treatment of spatial beam overlap and saturation, unpumped volume, intracavity losses, and a noninteger number of roundtrips in the unstable resonator are described. These result in the accurate simulation of injection-controlled laser performance over a wide range of unstable resonator magnifications, mirror spacings, and intracavity optical losses. Excellent agreement between calculated and experimentally observed energies and temporal profiles of the injection-controlled laser output was obtained.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

XeCl excimer laser ablation of a polyethersulfone film: Dependence of periodic microstructures on a polarized beam

Highly periodic stable microstructures appeared on the surface of polyethersulfone (PES) by XeCl excimer laser ablation with a single polarized beam in ambient air. Its formation mechanism was investigated using the time-resolved light scattering technique with the pulsed light of an XeF excimer laser. In addition to the polarization of the ablating beam, thermal processes on the etched surface play a significant role in microstructure formation.

350 nm laser radiation effects on Eu 2+ in alkali halides

Europium doped alkali halides, when irradiated by a XeF excimer laser, exhibit changes in their absorption spectra similar to those induced by ionizing radiation. Initial growth rates of the laser-induced absorption show a 3-photon absorption mechanism which, in turn, is used to address the nature of excited state absorption of europium in alkali halide hosts.

Phasefront preservation in high-gain Raman amplification

Experiments were performed to determine the degree of phasefront preservation possible in a high-gain, large-Fresnel-number number Raman amplifier. Phasefront information was encoded on a Stokes seed, which was then amplified in a 10-atm vibrational hydrogen Raman amplifier pumped by a XeF excimer laser. Interferometric data on the input and amplified Stokes beam indicate that their phasefront difference is less than 0.1 wave RMS. These results are consistent with the predictions of a numerical model of the Raman amplification process.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Spectral characteristics of an injection-controlled XeF(C→A) excimer laser

The spectral output characteristics of an injection-controlled XeF(C→A) excimer laser pumped by a short pulse (10 ns), high current density (250 A/cm2) electron beam are reported. A tuning bandwidth of 50 nm full width half maximum, centered at 490 nm, with a peak specific energy density of 1.3 J/ℓ was measured using an injection laser intensity of ∼2 MW/cm2. Continuously tuned output across the entire blue-green region (450–530 nm) with an energy density exceeding 0.2 J/ℓ was achieved. Injection beam spectral linewidths as narrow as 0.001 nm were shown to be preserved in the XeF(C→A) laser output.

An airborne compatible photofragmentation two‐photon laser‐induced fluorescence instrument for measuring background tropospheric levels of NO, NOx, and NO2

Reported on is a photofragmentation two‐photon laser‐induced fluorescence (PF/TP‐LIF) sensor with a demonstrated capability for making simultaneous measurements of NO/NOx/NO2. This instrumental technique is based on the direct spectroscopic detection of NO via the TP‐LIF methodology. The measurement of NOx (NO+NO2), and subsequently NO2, is accomplished by the photofragmentation of NO2 at 353 nm via a XeF excimer laser. The resultant NO photofragment is then quantitatively detected using the TP‐LIF technique. The laser photolysis efficiency for NO2 is typically 60% for NO2 photolysis cell residence times of less than 0.5 s. The limit of detection (S/N=2) for the described PF/TP‐LIF instrument is 3.5 pptv for NO (2 min integration time) and 10 pptv for NO2 (6 min integration time). An assessment of chemical interferences in this system revealed no significant problems. The extension of the PF/TP‐LIF methodology to the simultaneous detection of multiple NxOy, species is discussed.

Scaling characteristics of the XeF (C to A) excimer laser

The scaling characteristics and medium properties of an injection-controlled XeF(C to A) laser pumped by a 10-ns-high current density electron beam have been investigated. A five-component laser gas mixture, consisting of F/sub 2/, NF/sub 3/, Xe, Kr, and Ar was optimized for the scaled laser conditions, resulting in 0.8-J output pulses at 486.8 nm, corresponding to an energy density of small-signal-gain measurements combined with kinetic modeling permitted the characteristics of the dependence of net gain on the electron-beam energy deposition and gas mixture composition, resulting in an improved understanding of XeF(C to A) laser operation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Photochemical grafting of metal carbonyl clusters to inorganic oxides

Supported metal carbonyl clusters have attracted much attention in the preparation of catalysts containing highly dispersed metals on inorganic oxide supports. Typically such systems are formed by thermal activation until the cluster reacts with the surface hydroxyls. As a new approach, the photochemical grafting of metal carbonyl clusters to the surface of silica has been investigated by DRS uv-visible, FT-ir and ion exchange methods. It had been demonstrated that Fe 3 (CO) 12 can not be grafted to silica by thermal activation. However Fe 3 (CO) 12 physisorbed on silica was cleanly converted to the surface bound trinuclear hydrido anion cluster, HFe 3 (CO) 11 − , by room temperature irradiation at 450 nm. Os 3 (CO) 12 physisorbed on silica was converted by XeF excimer laser irradiation (351 nm) at room temperature to the surface attached species HOs 3 (CO) 10 -OSi≡. KrF excimer laser irradiation (248 nm) at room temperature led to a mixture of the attached trinuclear osmium cluster along with the attached mononuclear osmium carbonyl. KrF excimer laser irradiation at 173 K produced only the mononuclear species. These results have demonstrated the utility of a photochemical approach for the selective attachment of metal carbonyl clusters to the surface of inorganic oxides.

Selected area growth of GaAs by laser-induced pyrolysis of adsorbed triethylgallium

We report selected area growth of GaAs by XeF excimer laser induced pyrolysis of triethylgallium (TEGa) adsorbed on GaAs(100). TEGa dissociatively chemisorbs at 400 °C to form a stable layer which decomposes further under laser irradiation to liberate hydrocarbon products. The Ga left behind on the surface reacts with As2 and As4 (formed by pyrolysis of trimethylarsine or triethylarsine in a side tube) to grow GaAs in irradiated areas. Patterned films with feature sizes of ∼70 μm (limited by the projection system) were grown by this method. Interference between the incident beam and light scattered along the surface causes a substructure of parallel lines, with a spacing about equal to the laser wavelength (0.35 μm), to form on the features. This indicates that the ultimate spatial resolution is comparable to that predicted by thermal diffusion calculations (∼0.3 μm).

Observation of UV and violet diffuse bands of sodium dimer excited by XeF (351 nm) excimer laser

We report on the observation of strong UV diffuse band around 380 nm in direct one photon excitation of sodium molecule using 351 nm laser radiation from an excimer laser. The emission, though less intense by an order of magnitude in comparison with the violet bands, shows a clear spectral narrowing with increasing temperature. In addition, we report some interesting parametric dependences of the violet diffuse bands in the region of 420–460 nm. The results may help in clarifying the nature of the processes involved in populating the upper levels responsible for these emissions which have lately been conclusively identified.

Dissociation and vibrational relaxation of xenon monofluoride by various collision partners

Abstract : The removal rates of the lower levels of XeF strongly affect the overall efficiency of the XeF excimer laser operating on the B yields X transitions. We have deduced the removal rates of XeF(X,v = 3) in krypton, xenon, nitrogen, and carbon dioxide and the removal rates of XeF(X,v = 0) in sulfur hexafluoride by monitoring the populations of vibrational levels formed by the photolysis XeF2. The time history of the selected vibrational population is monitored with a continuous-wave (cw) tunable dye laser tuned to an absorption feature of the selected vibrational/rotational level. The studies show a rapid vibrational relaxation followed by a common decay rate of the coupled vibrational levels. The rare gases were found to remove XeF (X) with rate coefficients that differed from one another by less than a factor of 1.6. Larger removal rate coefficients were measured for molecular collision partners, with XeF2 having the largest rate coefficient. Rate coefficients were also determined for the concerted vibrational relaxation of v = 3 although the values do not represent state-to-state rate coefficients. Fast vibrational relaxation is required to empty the lower levels of the laser transitions so the vibrational bottlenecking does not terminate laser action prematurely. Keywords: Reaction kinetics.

Holographic Pattern Etching of Silicon—Carbide by Excimer Laser

ABSTRACTThe diffraction grating on SiC mirror was performed by a laser holographic method. In the present method, KrF laser and CIF3 was used for etchant gas. The ClF3 gas has an absorption band in the range between 200 and 400 nm. Therefore, CIF3 gas is effectively decomposed by the XeF, KrF and ArF excimer lasers' radiation. It is found that absorption of Si—C is about 50% in the range of between200 and 400 nm, and that the bonding energy of Si—C is lower than the photon energy of KrF laser beam. The above results indicate the direct decomposition of Si—Cbond. On the other hand, the threshold fluence energy for etching was 800 mJ/cm2 in 249 nm and in 193 nm as high as 7 J/cm2. In these results, the KrF laser is more effective than ArF laser. Then we applied KrF laser to crystalline SiC in an atmosphere of C1F3 gas. The divided two polarized KrF laser beams were interfered on the substrate. And the beams were used to photodissociated CIF3 gas in the proximity of substrate. Fluence of KrF laser beam was 1 J/cm2. The incidential angle of KrF laser beams was 20º and the grating gaps were 7170 Å, etching depth 1000 Å, and etching rate was 5 Å/pulse.

Analytical model for injection-controlled excimer laser amplifiers

A semiempirical model of a pulsed, injection-controlled laser is investigated analytically and is applied primarily to extensive experimental results that have been obtained for the XeF (C to A) excimer laser. The gain medium inside an unstable cavity is represented by a folded pulsed amplifier which is seeded by a narrowband input signal. A set of coupled rate equations for the population densities of the upper laser states, the wideband absorbers, and the photon flux was numerically integrated. Measured gain and absorption of the amplifier were used as input data to evaluate the model. Excellent agreement between calculated and experimentally observed peak intensity and various other pulse characteristics such as peak shape and laser pulse delay time was obtained. This model also predicts the experimentally determined injection-control threshold for KrF excimer lasers successfully, and should be applicable to numerous other injection seeded lasers.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Measurements of XeF ground state dissociation and vibrational equilibration

The removal rates of the lower levels of the XeF(B→X) excimer laser transitions strongly affect the overall efficiency of the E-beam-pumped devices. We have deduced the removal rates of XeF(X,v) in argon, helium, and neon by measuring the populations of vibrational levels v=0, 1, 3, and 4 formed by the photolysis of XeF2. The time history of each vibrational population is monitored with a cw tunable dye laser tuned to an absorption feature of the selected vibrational/rotational level. The studies show a rapid vibrational relaxation followed by a common decay rate of the coupled vibrational levels. Helium and neon were found to remove these levels with the same rate coefficient of (2.0±0.2)×104 (s Torr)−1 at room temperature. The corresponding rate coefficients for argon were larger by about 25%. The removal rate coefficients increased with temperature in the range of T=23–95 °C. The rate coefficient for the vibrational excitation of v=0 by helium was measured to be (3.6±0.7)×105 (s Torr)−1 at room temperature. This is considerably larger than the value of (4.8±1.5)×104 (s Torr)−1 previously reported by Fulghum et al. Fast vibrational relaxation is required to empty the lower levels of the laser transitions so that vibrational ‘‘bottlenecking’’ does not terminate the laser prematurely.