DE19501158C1 - Homogeneity testing device for optical glass or crystal - Google Patents

Abstract

The testing device uses a laser measuring system (1), supported by a stable carrier frame (2), together with a cooperating counter-mirror (3). The test sample (5) is displaced in coordinate directions in the laser measuring path (4) between the laser measuring system and counter-mirror. Setting elements controlled by an electronic levelling system are used for aligning the incidence face of the test sample at right angles to the laser beam. Pref. the levelling system uses a collimator (7) and an examination tube (8) with electronic image evaluation and microprocessor control of the setting elements.

Description

The invention relates to a device for homogeneity testing of optical glasses and crystals, preferably at small refractive index gradients using a laser path measurement system.

For measuring refractive index inhomogeneities with large gradients, like bubbles and streaks, comes mainly the shadow ver drive to Dvorak for application. With small gradients, i.e. H. slow change in the refractive index in the sample volume, caused by uneven cooling of the glass melt, are known the measurement by means of Fizeau or Michelson interferometer. The level passes through here Wavefront the specimen twice and is through the Refractive index inhomogeneities deformed. The receding wavefront with a wavefront reflected on the reference surface brought to interference and the resulting interference image evaluated numerically. The disadvantage here is that technical and financial reasons for this procedure Test specimen diameter is usually limited to <200 mm.

Measuring methods with autocollimators or are also known Diffraction interferometers, in which the specimen area is scanned. A more or less thick beam of light penetrates the test object in different grid points. By the refractive index inhomogeneities, the light becomes very small Distracted amounts in its direction, the distraction is detected and from this the resulting refractive index inhomogeneity is calculated. This has the disadvantage that the distraction Refractive index gradient is directly proportional. With very large ones Despite the large refractive index differences, test specimens can Refractive index gradient be very small, which results in the measurement results become inaccurate. Furthermore, the device structure is complicated and expensive.

From Glass Technology Vol. 2 No. 5 October 1961, pp. 192-198 it is known that the constancy of the refractive index is as Quality criterion for glass plays an important role and accordingly methods for the direct measurement of Glass inhomogeneities extremely important for the Are quality control. Here are the known methods called interferometry, shadow and streak methods. Furthermore, a method is presented which results from the Change in the transmission coefficient with a Immersion liquid coated sample qualitative statements about the homogeneity of the test object. This procedure is  however only applicable to relatively large fluctuations in the refractive index and difficult to quantify.

EP 00 85 981 A1 describes the refractive index gradient of light guide fibers using a special 2-wavelength interferometer measured. The transfer of this procedure to the Homogeneity measurement of vitreous bodies would be compared to that known methods with commercial interferometers none Bring advantages.

In Translated from Steklo i Keramika, No. 1, pp. 14-16, January, 1993 is also about microwaves measuring device relative to a scanner device a test object is moved to look for location-resolved errors, reported. The errors to be detected are primarily about material defects such as cavities, pores, gas and other inclusions, micro cracks or defects in the Crystal structure. The errors are recognized by Changes in the amplitude of the UHF radiation used. On quantifiable relationship between the change in amplitude and a possible refractive index inhomogeneity will not mentions what use for the purpose of highly accurate Measurement of refractive index gradients in the vitreous body as impossible lets appear.

According to the current state of knowledge, there is nothing more Method known with which the aim of the invention is different or can be realized cheaper.

The aim of the invention is to create a homogeneity measuring device, which excludes the previous disadvantages and its construction compared to conventional interferometers and other known device arrangements cheaper can be done.

The invention is based, through use a laser path measuring device with test pieces of any size to be able to measure with great accuracy. A leveling system should always be aligned perpendicular to the beam path Ensure the surface of the test specimen, causing measurement errors are largely avoided.

The measuring principle consists in determining the optical path 1 = d (x, y) _* n (x, y) determined by the test specimen thickness d (x, y) and the refractive index n (x, y). X and y are the location coordinates.

This task is carried out with a device with the features in Main claim solved. Further features according to the invention are characterized in the subclaims.

The advantage of the invention is that the specimen size is not limited, the laser path measuring system is extremely accurate and inexpensive to manufacture and even for very small ones Refractive index gradient is applicable. Furthermore, that is Measuring system less sensitive to mechanical vibrations as a Fizeau interferometer.  

Compared to the references mentioned, the method has the advantage of the highly precise quantifiability of the Measurement results.

The invention is described below based on the description of a Embodiment explained in more detail. In the associated Drawings show:

Fig. 1 The designation of the optical paths in the homogeneity measurement using a laser path measuring system.

Fig. 2 The arrangement of the modules.

The device consists of the actual laser distance measuring system 1, which is fixedly connected via a stable support structure 2 with the mating mirror. 3 In the beam path 4 , the test specimen 5 is attached according to an expedient grid in the x, y direction, and a test specimen surface is aligned perpendicular to the laser path measuring system 1 via actuators, which are controlled by an electronic leveling system 6 .

The leveling system consists of a collimator 7 and a test telescope 8 with electronic image evaluation via a PC 10 , which also controls the motorized actuators. The collimator maps a suitable line mark to "infinity". The light beam is reflected on the surface of the test object and reaches the test telescope, so that the real image of the line mark is created on the optoelectronic receiver connected to the test telescope. The position of the line mark image is evaluated by the evaluation unit 9 so that the tilt of the test specimen surface relative to the collimator and test telescope can be calculated. Signals for the actuators are obtained from the measurement results. This ensures a constant vertical positioning of the test specimen surface to the laser path measuring system.

The laser displacement measuring system measures the optical path differences in the the individual halftone dots against a fixed one Reference point so that the distribution according to 2 (n (x, y) d (x, y) - n (x₀, y₀) d (x₀, y₀)) can be reconstructed.

Reference list

1 laser displacement measuring system
2 stable supporting structure
3 mirror
4 beam path
5 candidate
6 electronic leveling system
7 collimator
8 test telescope
9 evaluation unit
10 pcs
11 actuators

Claims (4)

1. Device for checking the homogeneity of optical glasses and crystals, preferably with a small refractive index gradient, by means of a laser path measuring system, characterized in that the device consists of the actual laser path measuring system ( 1 ), which has a stable support structure ( 2 ) with the counter mirror of the laser path measuring system ( 3 ) is firmly connected, in the beam path of the laser path measuring system ( 4 ) the test specimen ( 5 ) can be moved according to an appropriate grid in the x, y direction and via actuators, which can be controlled by an electronic leveling system ( 6 ), a test specimen surface perpendicular to the beam path the laser path measuring system ( 1 ) can be aligned. 2. Device according to claim 1, characterized in that the leveling system consists of a collimator ( 7 ) and a test telescope ( 8 ) with electronic image evaluation ( 9 ). 3. Apparatus according to claim 1 and 2, characterized in that the electronic image evaluation via a PC ( 10 ), which also controls the motorized actuators, can be carried out. 4. Device according to one of claims 1 to 3, characterized in that that the laser path measuring system the optical path differences in the individual halftone dots opposite one put reference point so that their distribution after 2 (n (x, y) d (x, y) - n (x₀, y₀) d (x₀, y₀)) can be reconstructed.