Schott Glas

Other

Schott Ag

Carl-zeiss-smt Ag

Ewald Moersen

Burkhard Speit

Joerg Kandler

Wolfgang Singer

Frank-Thomas Lentes

Michael Gerhard

Eric Eva

Kurt Nattermann

Gunther Wehrhan

Axel Engel

Michael Thier

Hexin Wang

Harry Bauer

Thure Boehm

Christian Kusch

Lorenz Strenge

Peter Elzner

Hans-Joerg Axmann

Guenter Grabosch

Richard Schatter

Thorsten Reichardt

Hans-Josef Paus

Frank Richter

Christian Lemke

The method for determining local structures in optical materials, especially crystals, includes observing schlieren visually in a material to be tested with divergent white light in a first step; measuring birefringence of polarized laser light in the material to determine local defects and structure faults in the material with a spatial resolution of 0.5 mm or better in a second step if the material is judged to be suitable in the first step and then interferometrically measuring the material to determine the faults in the material by interferometry in a third step if the material is judged to be suitable in the first and second steps. This method can be part of a method for making optical components, especially for microlithography.

Method of determining local structures in optical crystals

In the method for growing large-volume monocrystals crystal raw material is heated in a melting vessel with heating elements to a temperature above its melting point until a melt is formed. A monocrystal is then formed on the bottom of the melting vessel by lowering the temperature at least to the crystallization point. A solid/liquid phase boundary is formed between the monocrystal and the melt. The monocrystal grows towards the melt surface in a direction that is perpendicular to the phase boundary. A vertical axial temperature gradient is produced and maintained between the bottom of the melting vessel and its upper opening and heat inflow and/or heat outflow through side walls of the melting vessel is prevented, so that the solid/liquid phase boundary has a curvature radius of at least one meter. A crystal-growing device for performing this process is also described.

Method and device for growing large-volume oriented monocrystals

The method for evaluating schlieren in glassy or crystalline optical materials includes irradiating a test sample of the optical material with light and producing a shadow image of the test sample on a projection screen. The shadow image of the test sample is received in an electronic image receiving device, such as a digital camera, and is compared with another shadow image of schlieren obtained with a comparison sample by means of interferometry. Then the optical material of the test sample is evaluated with the help of the comparison results.

Method and apparatus for analysis of schlieren

The optical system has a first optical element ( ) and a second optical element ( ) having respective plane surfaces and cubic crystal structures, which are arranged next to each other along an optic axis ( ) so that one of the crystal axes of each optical element is parallel to the optic axis and the plane surfaces are resting against each other. The first and second optical elements have first and second orientations in relation to the optic axis, which are preferably rotated by a rotation about the optic axis ( ) with respect to each other according to the rotational symmetry of the material. At least one of the first optical element and second optical element is pre-stressed by applying a compressive stress (&sgr;,&sgr;, ) thereto. The compressive stress is applied radially symmetrically in a plane perpendicular to the optic axis ( ) and compensates for spatial dispersion.

Optical system with compensated spatial dispersion

A method of making a fracture-resistant large-size calcium fluoride single crystal is described, which is suitable for an optical component for radiation in the far UV range. The calcium fluoride raw material for the single crystal is first melted and subsequently solidified by cooling the melt to form a single crystal. However the calcium fluoride raw material is doped with from 1 to 250, preferably 1 to 100, ppm of strontium, preferably added as strontium fluoride, and contains from 1 to 10 ppm of sodium as well as up to 100 ppm of other impurities.

Method of making a fracture-resistant calcium fluoride single crystal and its use

The method for determining radiation stability of a crystal to radiation of a working wavelength to be employed in a subsequent application includes taking a first absorption spectrum (A) of a cleaved piece of the crystal with a given thickness (D) over a predetermined wavelength range from a first wavelength (&lgr; ) to a second wavelength (&lgr; ) by means of a spectrophotometer. Then the cleaved piece of the crystal is irradiated with an energetic radiation source so as to form all theoretically possible color centers (saturation). After the irradiating a second absorption spectrum (B) of the cleaved piece of crystal is taken over the same predetermined wavelength range. Then a surface integral of a difference spectrum of the first absorption spectrum and the second absorption spectrum over the predetermined wavelength range is formed and divided by the thickness (D) to obtain a scaled surface integral value. The absorption coefficient &Dgr;k at the working wavelength for the subsequent application is then obtained preferably from the scaled surface integral value for the damage induced by the energetic radiation and a calibration curve relating the absorption coefficient at the working wavelength to the surface integral of the absorption coefficient induced by the energetic radiation.

Method for determination of the radiation stability of crystals

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Mainz, Germany

Ewald Moersen