The use of silica lenses in a photolithographic system employing a 193 nm excimer laser has been proposed. It is desirable to determine if, at the low intensity to be used in the system (approximately equals 0.1 mJ/cm²), the glass will withstand about ten years of use without objectionable induced absorption. At a pulse frequency of 1 Khz, this length of time corresponds to about 10¹¹ pulses. Because of the long time involved, an accelerated test is needed to determine the susceptibility of silica to induced absorption. The mechanism of darkening must be understood in order that the behavior of the glass under use conditions be predicted with confidence from the results of the accelerated test. The most important processes in the mechanism of induced absorption are: (1) Two photon absorption creating an exciton; (2) Trapping of the exciton by a localized state; (3) Dissociation of the trapped exciton to form an E' center and a NBOHC; (4) Reaction of these centers with hydrogen to form SiH and SiOH bonds; and (5) Photolysis of the SiH bonds to produce more E' centers. The mechanism will be discussed in detail and the agreement with experimental results over a range of intensities and hydrogen levels will be presented.

SCHOTT ML (MicroLithography) is presented as the world's first supplier of optical materials for all current generations of wafer steppers: i-line-glasses for 365 nm, fused silica for 248 nm/193 nm and CaF₂ for 193-nm microlithography. I-line-glasses are presented optimized in transmission, solarization and refractive index homogeneity for application in high performance i-line-scanner systems for such 0.25 micrometers mix and match technology. The focus for fused silica is laid on laser damage performance, essential for application in 193 nm lithography. An experimental setup is shown, allowing a fast evaluation of materials respecting laser induced fluorescence and absorption. First data of a 193 nm marathon test on SCHOTT ML fused silica are presented. Use of CaF₂ in ArF projection optics requires improvement of crystal growth processes and equipment. The progress achieved in refractive index homogeneity, stress birefringence and transmission is presented. High laser damage resistance for ArF illumination optics was also accomplished. Common requirement for mass production of all high grade optical materials is the ability for accurate material characterization. Status of measurement and characterization equipment is presented for selected optical properties.

The applications of chalcogenide glasses (CG) and the structures on their base in the microlithography are reviewed. In brief are described the properties of high resolution inorganic thin film structures CG-Ag and CG layers. The properties of such resists and peculiarities of UV and laser lithography were investigated. Study of photostimulated processes in inorganic resists are of considerable interest both for fundamental science and practical applications. The photodoping effect is most typically manifested in the Ag-As₂S₃ system. In most studies this structure is used as a model one. Surface plasmon resonance was applied to study the initial stages of kinetics of the photostimulated interaction in an inorganic resist (Ag-As₂S₃ system). This method allows to measure the optical constants of ultrathin (0.5 up to 100 nm) films and to observe their structural changes and thickness evolution in real time scale. From the results obtained it can be concluded that during the photoexposure process the Ag-As₂S₃ system can be considered as a four-layer system: the first layer-silver, the second one- silver sulfide, the third one-As₂S₃ photodoped with silver, the fourth one-the As₂S₃ layer that has not interacted with silver yet. During the exposure process the intermediate silver sulfide layer thickness remains practically unchanged. Using the As₂S₃ or As-S-Se layers the minimal width of lines 170 nm was obtained, under the exposure wavelength 532 nm.

Last year we presented the first experimental measurements of the dispersion in GRADIUM^TM glasses. These measurements provided a glimpse into the materials properties that had previously been approximated. Unfortunately, although these valuable measurements provided broad spectrum information about the material, these measurements did not provide the precision required for many white-light applications. Furthermore, it was clear last year that the modeling must be improved because of the need to accurately model the material over the natural transmission window of the glass. Therefore, LightPath has undertaken a program to provide improved experimental characterization of current and new GRADIUM materials as well as improved modeling. Experimental data will be available soon. We will therefore evaluate the accuracy and limits of dispersion modeling using the modified Sellmeier approach. We will also present some empirical guidelines for the number of coefficients required for high-precision, wide spectral band modeling.

Recent interest in monitoring systems requires very large optical windows that are transmitting over a wide spectral range. Some of the other requirements involve durability, high strength and robustness to withstand severe environments. Therefore, sapphire has been required for these applications. The Heat Exchanger Method (HEM)^TM has been used to produce very large sapphire crystals primarily for optical applications. Crystals of 20 cm and 25 cm diameter have been produced in production for over 20 years. Presently, 34 cm diameter boules have been adopted in production, and 50 cm diameter sapphire growth is currently in development. Results of progress and characterization data of the boules will be presented.

Chalcogenide glasses have been produced commercially for use in infrared systems for almost 50 years. Only three glass compositions in the western world have been produced and used in ton quantities: As₂S₃, Ge₃₃As₁₂Se₅₅, and Ge₂₈Sb₁₂Se₆₀. Production of these three compositions at Amorphous Materials will be discussed. Physical properties of the glasses will be compared and related to the properties of other IR optical materials. Drawing of chalcogenide glass fibers at Amorphous Materials will be described.

The current research demonstrates the effectiveness of both silicon and germanium as transmissive materials for use within the far infrared wavelength range of 20 to 160 microns. This study involves samples with a wide range of resistivities and temperatures including: n-type Si of 4000, 2000, 160, 65, 12, and 2.6 ohm-cm and p-type Si of 500 and 60 ohm-cm within a temperature range of -100 degree(s)C to 250 degree(s)C and n-type Ge of 39, 25, 14.5, 5.0, 2.5, and 0.5 ohm-cm within a temperature range of -100 degree(s)C to 100 degree(s)C. Far infrared absorption mechanisms are briefly discussed. The experimental absorption data are used to discuss the interaction between absorption by lattice resonance and free carrier absorption. Highly resistive germanium and silicon are both found to be excellent transmissive materials in the far infrared. These studies may be used to develop the feasibility of silicon and germanium as optical windows or lenses within an extraterrestrial environment.

As compared to multicomponent optical glasses, when fused silica optical glass (pure SiO₂) is ground or polished, it exhibits unique features, such as low surface microroughness and subsurface damage, low grinding-induced residual stresses, and low removal rates. On the other hand, fused silica glass is known to densify permanently when subjected to sufficiently large compressive stresses. Such densification, manifested as a permanent increase in the index of refraction, is facilitated by shear stresses. We discuss a simple constitutive model describing the densification of fused silica, under large applied model to interpret nanoidentification tests of fused silica over loads in the range 1 - 100 mN (about 0.1 - 10 gf) via finite element simulations of indentation of an axisymmetric half- space by a conical indenter with a spherical tip. Such geometry resembles the action of polishing and microgrinding abrasives used in optics manufacturing. The fused silica nanoindentation data are compared to other optical glasses such as BK7 and LHG8.

Electrochromism in sol-gel deposited WO₃ films containing TiO₂ has been observed. The films are deposited by spin coating from peroxo-polytungstic acid and titanium isopropoxide precursors. The films were fabricated on quartz and SnO₂:F coated glass substrates. Films were heat treated at 150 degree(s)C. Morphology of the films was examined by scanning electron microscopy, which indicated that the films were smooth and had a pore free surface. Results will be presented detailing the optical switching during electrochemical lithium intercalation. These results will be used to compare the performance of the Ti doped WO₃ films with other electrochromics. The Ti:WO₃ films all color cathodically, and the color state is a neutral grayish blue color, while the bleached state is transparent and colorless. Results of the cyclic stability will also be presented. The neutral color of the Ti:WO₃ films means that electrochromic windows based on Ti:WO₃ may have significant advantages over WO₃-based windows. A detailed analysis of the optical properties of the bleached and colored states of the films will be presented. The dynamics of coloration for these films is also under investigation, and preliminary results will be presented.

In this paper, we present an analysis of optical amplification properties of Nd-doped planar waveguides on glass substrates fabricated by sol-gel process. Modified gain characteristics are determined from the susceptibility profile and the waveguide dispersion properties. The waveguide dispersion properties are represented by the propagation coefficient variation with optical frequency, (beta) ((omega) ). This is determined by solving the non- linear dispersion equation using the waveguide structural parameters, such as, the transverse refractive index profile, the waveguide film thickness and the operating optical frequency. The susceptibility profile, (chi) ((omega) ), is determined using the measured absorption spectra from the fabricated waveguide samples. The analysis is facilitated by fitting an appropriate Gaussian distribution to the measured absorption spectra at the resonant frequency. It is observed that the gain profile is modified asymmetrically by the waveguide parameters.

Micro-Raman and photoluminescence (PL) studies of Zn_xCd_1-xSe (x equals 0.68) thin film have been carried out under high pressure at room temperature. In the PL spectra, the PL energy gap shift exhibits sublinearity with pressure and a least-square fitting to the experimental data gives a pressure coefficients of (alpha) equals 0.083 eV/GPa and (beta) equals 0.0052 eV/GPa². The second-order pressure coefficient (beta) of the energy gap obtained experimentally is anomalously large and its origin was explained by alloy potential fluctuation with increasing pressure. In the Raman spectra, the first-order pressure coefficient was also calculated by least-square fit. The low energy tail of the longitudinal-optical phonon was found to develop with pressure for the first time, and the line shape change with pressure is interpreted in terms of a `spatial correlation' model.

Investigated is the influence of doping with thulium on the character of solidification and luminescent properties of lithium tetraborate (LBO). It is found that the increase of thulium content favors crystallization of the melt preventing its vitrification. The character of the luminescence spectra of LBO:0.4%Tm³⁺ glass and LBO:0.5%Tm³⁺ polycrystal testified that in both cases the emission of Tm³⁺ ions in the low-symmetry surroundings of the matrix ions takes place under the influence of static electric fields.

In this paper, photorefractive (PR) crystals of Cu and Mn- doped (K_0.5Na_0.5)_0.2(Sr_0.75Ba_0.25)_0.9Nb₂O₆ were symmetrically studied. We reported the growth conditions, the absorption properties and the photorefractive properties including two wave mixing (TWM) and self-pumped phase conjugation (SPPC). The mechanism of Cu-doped KNSBN was referred briefly, and the influence of the different sites occupied by doping ions on PR properties was also discussed. All these results reveal that: (1) In Cu-doped KNSBN crystals, the photorefractive properties become better with the increase of the doping level, such as higher effective charge carrier density, larger coupling coefficient, faster response rate, higher SPPC reflectivity. (2) The thinner sample shows larger coupling gain coefficient, which is due to the light creep effect and beam fanning effect. The response time becomes shorter with the decrease of the thickness. (3) In Cu:KNSBN crystals, the coupling gain coefficient of TWM was obtained up to 35 cm^-1. (4) In Cu:KNSBN and Mn:KNSBN samples, the SPPC reflectivity up to 73% have been obtained, respectively. (5) The C-site in the tungsten-bronze structure of KNSBN has an effect on the PR properties of the crystal. All these results show that doping in KNSBN is an effective method to improve the PR properties. The Cu-doped KNSBN crystal is a very promising photorefractive material.

Time-resolved photoluminescence spectra of various grade CaF₂ single crystals were measured to examine effectiveness as a diagnosis for ArF excimer laser damage. Luminescence upon exciting with ArF laser light was classified into four bands from the peak position and lifetime, i.e., (1) 274 nm, 1 microsecond(s) , (2) 541 nm, 1 ms, (3) 418 nm, 700 ns, and (4) a doublet band 309 and 330 nm, 30 ns. Band 1 is emitted via 2-photon absorption processes and the origin is the relaxation of self-trapped exciton generated by band-to-band excitation. Therefore, this band is intrinsic to CaF₂ crystals. On the other hand, the bands 2, 3 and 4 originate from trace impurities. Tb³⁺, Eu²⁺ and Ce³⁺, respectively. These luminescence bands occurred via on-photon absorption processes. When the band 2 (yellow green light) was clearly observed during the laser irradiation, the intense absorption band due to an F center associated with a trivalent yttrium ion was induced after prolonged irradiation. On the other hand, the band 3 (blue light) had no relationship with color center formation. It was suggested that photo-oxidation of trivalent rare earth ions has a correlation with color center formation.

Photochemical reactions at the solid surface can be applied for the microstructuring. Photochemical processes have high anisotropy and don't produce radiation defects in surface layers of materials, providing certain advantages compared to ion, plasma and X-ray technologies. At the moment the most of photoexcitation sources use visible near UV photon range. The increasing of photon energy up to VUV by use of synchrotron radiation (SR) or other source leads to diminishing of the microstructure size to 100 nm and rising of the quantum efficiency of the reaction. In this work photochemical reaction of etching of ZnSe has been studied. Surface of ZnSe crystal (110) was irradiated with photons 4.5 eV < hv < 50 eV (SR) in the chlorine atmosphere at room temperature. By means of XPS, SEM, EDS chemical composition and thickness of the reaction products have been defined. It was shown that the reaction products layer contain of ZnCl₂ with thickness of 100 nm. Evaluated quantum efficiency was about 1. Further, it was demonstrated the possibility of microstructuring at ZnSe surface by photochemical etching with the use of special masks.

The authors reports in this paper a sensitive method for measuring low-level linear birefringence in optical materials. A photoelastic modulator is employed as the polarization modulation device in the set-up. The sensitivity of this method is evaluated to be at approximately 0.003 nm (approximately 0.002 degree(s) at 632.8 nm) by measuring the mechanically induced linear birefringence in a fused silica optical element. The capability of this method is demonstrated by determining the residual linear birefringence below 0.1 nm in several high quality optical elements.

Cylindrical and rod gradient-index lenses with numerical apertures of 0.5 are produced by silver ion exchange in a sodium-aluminosilicate glass. Choosing the appropriate glass composition enables the generation of refractive index changes of 0.145 in the glass without coloration in the visible range. Diffraction-limited optical performance of lenses of up to 1.3 mm in thickness or diameter is achieved by ion exchange modeling which comprises the following steps: (1) The concentration-dependent diffusion coefficient of the glass is experimentally determined by the Boltzmann- Matano method, (2) Process control is provided by the measured dopant concentration/refractive index relation and the glass/salt equilibrium dependence, (3) The ion exchange process is optimized by solving the non-linear diffusion equation for two steps under different boundary conditions, (4) Diffraction-limited lenses up to numerical apertures of 0.5 are generated by applying the optimized process parameters to the ion exchange.

Color center formation in AlF₃-YF₃-RF₂ (R equals alkaline earth metal) glasses doped with PO_2.5 (0 - 3 mol %) by irradiation with ArF excimer laser light was examined by optical absorption (vuv-visible) and electron paramagnetic resonance spectroscopies. Impurity iron ions and oxygens in the samples were 0.2 ppm and 440 ppm, respectively. Optical absorption ranging from 2 - 8 eV was induced via one-photon absorption processes. The optical band dominating the transmission loss at 193 nm has the peak at 5 eV in the P-free glasses or the peak at 6.9 eV in the doped glasses. The origins of the 5 ev-band and the 6.9-ev were tentatively ascribed to an oxygen-related hole center giving an EPR signal at g equals 2.0097 and PE'-center giving a hyperfine doublet with a separation of approximately 70 mT. The oscillator strengths of the 5-ev band and the 6.9-ev band were calculated as approximately 0.2 and approximately 0.13, the latter being close to that of Si E'-center. No formation of color centers associated with Al, Y, R and F ions was observed. The present results suggest that the reduction of impurity oxygen is a route to effectively suppress the solarization in the P-free AlF₃-based glasses.