Fused Silica Prism Research Articles

High-accuracy measurement of the optical transmittance of optical bulk materials at deep-ultraviolet wavelengths.

A measurement setup that is capable of measuring the internal transmittance of fused-silica prisms at 193 nm with a precision better than 0.01%/cm (3sigma) is presented. Its application to materials and wavelengths other than those that were chosen here for demonstration is straightforward. A lack of any standards makes it impossible to determine the absolute accuracy (also called measurement uncertainty) experimentally; however, calculations indicate that it is almost within the same margin as the precision.

Prism spectroscopic ellipsometer

A conventional prism spectrometer is converted into a transmission spectroscopic ellipsometer (TSELL) by using the prism itself as the sample or substrate. An obliquely incident collimated broadband beam of light is dispersed by the prism into its colors, which are focused by a lens onto a linear detector array. A rotating achromatic linear polarizer is inserted in the incident beam, and a fixed linear analyzer is placed in front of the detector array. Fourier analysis of the output signal as a function of the polarizer azimuth, on a pixel-by-pixel basis, yields the transmission ellipsometric parameters ψ t(λ) and Δ t(λ) as functions of wavelength λ. For a given uncoated prism, the deflection angle γ(λ) and the base-line SE data of ψ t(λ) can be inverted to yield the prism refractive index n p(λ), or the constant coefficients of an appropriate dispersion relation for the prism material. When the prism is coated by a transparent or semitransparent thin film, the TSELL data of ψ t(λ), Δ t(λ) enable the determination of the thickness d and optical constants n f(λ), k f(λ) of the film. As an example, the potential of TSELL is illustrated using simulated TSELL spectra for a fused-silica prism that is coated with a ZnS film.

Analytic expressions for the fourth- and the fifth-order dispersions of crossed prisms pairs.

In case of tunable ultrashort-pulse lasers, besides the prism material, separation, and insertion, one may choose the central wavelength providing a better high-order dispersion compensation. Because of errors that accumulate in numerical iterations, the analytic approach may be preferable for high-order dispersion examination. Analytic expressions for the fourth- and the fifth-order dispersions of crossed prisms pairs, both at arbitrary and Brewster-angle incidences are presented. Examples are given for e-sapphire slabs and for one or two pairs of fused-silica prisms. Results are shown providing compensation of both the second- and the third-order dispersions, by keeping as low as possible the higher-order ones.

Probing Adsorption, Orientation and Conformational Changes of Cytochrome c on Fused Silica Surfaces with the Soret Band

The Soret absorption band has been utilized as a probe for the adsorption of cytochrome c to the surface of a fused silica prism in direct contact with bulk protein solutions of various concentrations and pH. Employing linear polarized light and a single-pass total internal reflection absorption technique, we examined in detail the adsorption isotherm, molecular orientation, packing density, and conformational change of the protein bound to the bare (hydrophilic) and silanized (hydrophobic) glass surfaces. An adsorbate density of Γ = 1.4 × 1013 molecules/cm2 was determined for the hydrophilic substrate at pH 7.2 and Cb = 110 μM, indicating that the protein molecules are essentially closely packed on the surface at saturation. The packing density is sensitive to the solution pH as well as the surface hydrophobicity, a result that the protein−surface interaction is governed by both electrostatic and hydrophobic forces. The same forces also govern the molecular orientation, yielding an angle of θμ = 41° between the heme plane and the surface normal at neutral pH. The angle is retained over a wide pH range (4−9) and is fairly independent of the surface coverage on both the hydrophilic and hydrophobic substrates. Reorientation of the protein occurs (41° → 20°) at pH ≈ 3, when the cyt c unfolds and the hydrophobic force becomes dominant in the adsorption process.

Sequence effect of optical elements in a femtosecond Ti:sapphire laser oscillator

We have numerically and experimentally verified that the sequence of optical elements in a femtosecond Ti:sapphire laser affects the laser’s characteristics. Even with the same net dispersion in a cavity, the output spectrum showed a significant change in width and shape when the sequence of dispersive elements was changed in a Kerr-lens mode-locked Ti:sapphire laser with fused-silica prisms for dispersion compensation. It was also shown that the output coupler’s position can affect the dynamics of pulse formation by the combined action of output coupling and self-phase modulation. We explain such phenomena based on pulse formation in a laser cavity with discrete distribution of dispersion and self-phase modulation.

Generation of sub-10-fs pulses from a Kerr-lens mode-locked Cr^3+:LiCAF laser oscillator by use of third-order dispersion-compensating double-chirped mirrors

Pulses as short as 9 fs at 220-mW average power and a 97-MHz repetition rate are generated from a cw Ti:sapphire-pumped Kerr-lens mode-locked Cr(3+)LiCAF laser oscillator employing broadband double-chirped mirrors for second- and third-order dispersion compensation. Fine adjustment of dispersion is accomplished with a fused-silica prism pair. The result demonstrates that Raman-induced self-frequency shifting of the pulse does not limit sub-10-fs pulse generation from colquiriite crystals.

Real-time characterization and optimal phase control of tunable visible pulses with a flexible compressor

The output pulses of a noncollinearly phase-matched optical parametric amplifier (NOPA) are fully characterized by spectral phase interferometry for direct electric-field reconstruction (SPIDER). The SPIDER setup has been optimized for online diagnosis of tunable visible pulses with a 1 kHz repetition rate and 10–40 fs duration. The compression of the NOPA pulses by different prism sequences and commercially available chirped mirrors is investigated. For flexible phase control the end mirror of a fused-silica prism compressor has been replaced by a deformable mirror. With an evolutionary strategy guided by the spectral phase information of the SPIDER, optimal compression of the NOPA pulses to a 7.6 fs duration is achieved.

45° slanted fibre Bragg grating design with prism coupled holographic exposure

A holographic technique for forming 45/spl deg/ tilted fibre gratings using two 45/spl deg/-90/spl deg/, -45/spl deg/ fused silica prisms is described. The technique reduces fringe distortion due to the lens effects of the fibre during exposure. Details of the experimental system and grating performance are given.

Molecular fluorescence in the vicinity of a nanoscopic probe

The dramatic modifications of molecular fluorescence in the proximity of a sharp nanoscopic probe is investigated by an apertureless or antenna-based near-field scanning optical microscope, which exploits the interactions between a fluorescent sample and a laser illuminated Si atomic force microscope probe. Specifically, luminescence is monitored from evanescently excited, dye-doped polystyrene nanospheres (RS=20–80 nm) on a fused silica prism surface as a function of probe-sample geometry. The incident laser field is enhanced in the near-field of the probe tip, resulting in images with high sensitivity (σmin≈2 Å2 in a 1 Hz detection bandwidth) and strongly subdiffraction-limited spatial resolution. At probe-sample distances greater than ≈λ/2, the images are dominated by far-field interference between (i) direct fluorescence from the molecular sample and (ii) indirect fluorescence from image dipoles induced in the atomic force microscope probe. Near-field “shadowing” of the molecular fluorescence by the probe also occurs and is studied as a function of probe-sample-detector geometry. Finally, effects of probe-sample proximity on the fluorescence emission spectrum are investigated. In summary, the data elucidate several novel near- and far-field molecular fluorescence enhancement effects relevant to further development of molecular and nanostructural spectroscopic methods with spatial resolution well below the diffraction limit.

Liquid immersion deep-ultraviolet interferometric lithography

An apparatus for deep-ultraviolet interferometric lithography is described, in which the interfering beams illuminate the substrate through a fused silica prism and a layer of index-matching liquid. The liquid-immersion technique was found to be compatible with a commercially available, chemically amplified photoresist. The apparatus was used with a 257 nm light source to write gratings having a period of 97 nm and linewidth of approximately 40 nm.

Contrasting damage characteristics in direct incidence and surface plasmon mediated single-shot laser ablation of aluminium films

Thin, oxidised Al films grown on one face of fused silica prisms are exposed, under ambient conditions, to single shots from an excimer laser operating at wavelength 248 nm. Preliminary characterisation of the films using attenuated total reflection yields optical and thickness data for the Al and Al oxide layers; this step facilitates the subsequent, accurate tuning of the excimer laser pulse to the surface plasmon resonance at the Al/(oxide)/air interface and the calculation of the fluence actually absorbed by the thin film system. Ablation damage is characterised using scanning electron, and atomic force microscopy. When the laser pulse is incident, through the prism, on the sample at less than critical angle, the damage features are molten in nature with small islands of sub-micrometer dimension much in evidence; a mechanism of film melt-through and subsequent blow-off due to the build up of vapour pressure at the substrate/film interface is appropriate. By contrast, when the optical input is surface plasmon mediated, predominately mechanical damage results with the film fragmenting into large flakes of dimensions on the order of 10 μm. It is suggested that the ability of surface plasmons to transport energy leads to enhanced, preferential absorption of energy at defect sites causing stress throughout the film which exceeds the ultimate tensile stress for the film; this in turn leads to film break-up before melting can onset.

Evanescent wave cavity ring-down spectroscopy for probing surface processes

Sub-monolayer detection of adsorbed I 2 is demonstrated with the cavity ring-down technique by using intra-cavity total-internal reflection to generate an evanescent field that probes the adsorption process. A precision, fused-silica Pellin-Broca prism with ultra-smooth facets (surface roughness ∼0.05 nm r.m.s) is employed to provide the intra-cavity TIR. The known cross-section for the 1Σ g +→ 3Π u transition of I 2, which is largely invariant between pressure-broadened gaseous, weakly chemisorbed, and liquid states, provides quantification of sensitivity. A minimum detectable coverage of ∼0.04 monolayer is determined at a weakly absorbed probe wavelength.

Sub-20-fs tunable pulses in the visible from an 82-MHz optical parametric oscillator

We have produced pulses tunable in the 590-666-nm range, with durations down to 13 fs, using an 82-MHz Ti:sapphire second-harmonic-pumped, high-bandwidth, beta-barium borate optical parametric oscillator in a fused-silica prism group-delay-dispersion-compensated, six-mirror folded ring cavity.

THE HIGH-RESOLUTION CROSS-DISPERSED ECHELLE WHITE PUPIL SPECTROMETER OF THE MCDONALD OBSERVATORY 2.7-M TELESCOPE

ABSTRACT A new high-resolution cross-dispersed echelle spectrometer has been installed at the coude focus of the McDonald Observatory 2.7-m telescope. Its primary goal was to simultaneously gather spectra over as much of the spectral range 3400A to 1 micron as practical, at a resolution R = lambda/delta-lambda ≃ 60,000 with signal-to-noise ratio of ~100 for stars down to magnitude 11, using 1-hour exposures. In the instrument as built, two exposures are all that are needed to cover the full range. Featuring a white-pupil design, fused silica prism ross disperser, and folded Schmidt camera with a Tektronix 2048 X 2048 CCD used at either of two foci, it has been in regularly-scheduled operation since April 1992. Design details and performance will be described.

Generation of 11-fs pulses from a self-mode-locked Ti:sapphire laser

By optimizing the intracavity dispersion compensation in a self-mode-locked Ti:sapphire laser, we have generated pulses of 10.95-fs duration. Dispersion within the laser cavity is reduced by use of a short 4.5-mm highly doped Ti:sapphire crystal and fused-silica prisms. The output from the laser has an average power of as much as 500 mW, with a wavelength centered at 780 nm and a bandwidth of 62 nm. Our results demonstrate that the exceptionally broad bandwidth of Ti:sapphire can be utilized to generate pulses that, to our knowledge, are shorter than has been possible with any other type of laser material to date.

Probable Errors in the Internal Reflection Method for Optical Constant Measurements

The internal reflection method (IRM), recently developed for optical constant measurements of deposited films, was investigated in terms of probable errors. The optimum angle of incidence for IRM was shown to lie in the range of 60°-75°. With these incident angles, IRM using a fused-silica prism demonstrated the effect of reducing the probable errors to a few tenths of those in the ordinary free surface reflection method.

Wetting layers and dispersion forces for a fluid in contact with a vertical wall.

Ellipsometric measurements of the thickness of the wetting layer of sulfur hexafluoride that forms on a fused-silica surface partially immersed in the liquid are presented. The components of the experiment included a He-Ne laser (0.6328 micron), polarizer, and quarter-wave plate with 45-deg azimuth. An optical-grade fused-silica prism was polished to wavelength/20, and strain-induced birefringence was accounted for. It was found that the layer thickness decreases from 40 to 20 nm with a height increase from 0.7 to 3 mm above the liquid-vapor interface. The thickness is independent of the temperature between 10 and 0.1 K below the critical temperature (319 K). The results are compared in detail to the theory of Dzyaloshinskii et al. (1961), and are noted to coincide closely.

Compensation of Inhomogeneity in Polishing Fused Silica Prisms

An experiment is attempted to improve the resolution of a Littrow type spectrograph. It is ascertained that inhomogeneity of fused silica can be compensated successfully by local polishing of the surfaces of prisms, except for those which have very complex inhomogeneity.

Calibration of prism spectrometers in the ultraviolet, visible and near-infrared regions

Emission line spectra of the elements Hg, Cd, Zn, He, Ne and Rb were used in the development of a precise and comprehensive calibration procedure for the fused silica and DF-2 glass prisms covering the range 0.194 μ < λ< 2.33 μ and 0.365 μ < λ < 2.33 μ, respectively. Spectrograms of the emission lines are presented together with experimental conditions necessary to reproduce them, the photon energy and vacuum wavelength of each identified line, as well as other pertinent information. Since the emission lines are very narrow and their wavelength values are accurately known, the precision of the method is determined only by the experimental uncertainty in obtaining the corresponding spectrometer drum readings. Data are reported for 233 lines observed with the fused silica prism and for 341 lines with the DF-2 glass prism. The observations were made with a Perkin-Elmer Model 13-U single-pass spectrometer using Osram spectral lamps. The detectors used were the RCA photomultiplier type 7200 for the ultraviolet and visible regions, the type 1P21 for the visible region (in which it has a better S N ratio than the 7200), and the PbS photoconductive detector for the near infrared. A discussion of experimental aspects is presented including details on spectrometer arrangements and problems of technique. In addition, a procedure was developed to provide a definitive and precise method for plotting the final calibration curves in terms of photon energy versus spectrometer drum reading, based on a modification and extension of the empirical relationship of McKinney and Friedel. A detailed description of the adaptation and the application of this procedure is given, together with the modified equation and typical values of its constants pertinent to each prism.