WO2009040158A1 - Probe and device for the optical testing of measurement objects - Google Patents

Abstract

The invention relates to an optical probe (1) for the optical testing of measurement objects, comprising: an input (10) for introducing an input beam into the probe (1), a GRIN lens (8) (gradient-index lens) for focusing the input beam into a measurement beam, and an output (20) for illuminating the measurement objects to be tested, wherein the GRIN lens (8) comprises at least one surface (9) that is inclined relative to the direction (7) of the input beam for deflecting the measurement beam. The invention further relates to a device for the inferferometric measurement of measurement objects, wherein an interferometer is connected to the optical probe (1) in the device.

Description

 Probe and device for optical testing of test objects

State of the art

The invention relates to an optical probe for the optical testing of test objects according to the preamble of claim 1 and to an apparatus for the interferometric measurement of test objects with the probe.

To obtain surfaces of a measurement object, e.g. of a component, an optical probe can be used. An example of such an optical probe, which is also commercially available, is shown schematically in FIG. The

Probe 1 has an input 10 for introducing an input beam into the probe 1, a lens 8 for focusing the input beam to a measuring beam and an output 20 for illuminating the measured objects to be tested.

The input beam is introduced through an optical fiber 11 in the probe 1, wherein for the coupling of the optical fiber 11 in the probe 1, a ferrule 2 is provided. Between the ferrule 2 and the lens 8 for focusing a spacer 4 ("spacer") can be arranged.

The lens for focusing the input beam into a measuring beam is often a so-called GRIN lens 8, which is a short form of "graduate index lens", "graded index lens" or "gradient index lens." Unlike conventional lenses The refractive index of a GRIN lens changes continuously and steplessly in the material of the lens be dispensed with a curved surface shape as in the case of conventional lenses.

The focused measurement beam is finally deflected from its original direction to the side via a prism 3, which is arranged at the output 20, and thus illuminates the surface of the measurement object.

Also described in DE 100 57 539 A1 is an interferometric measuring device which is connected to an optical probe part. It is proposed to also provide a GRIN lens as an optical element in the probe. Further, its front, the measuring object facing area is designed as a measuring head. The measuring head is provided with a thin, designed as a measuring fiber optical fiber whose free end portion is designed as an end piece for illuminating a measuring point of the measurement object and receiving reflected measurement light. For the deflection of the measuring light, the tail is bevelled and mirrored.

An optical probe with a GRIN lens is also known from EP 1 222 486 B1. Here is described the construction of a probe for use as a medical device, for example an endoscope. In the probe is next to the

GRIN lens provided a separate mirror for beam deflection.

From US 6,654,518 Bl an optical collimator for optical signal transmission is known, in which a GRIN lens is provided with inclined surfaces to couple incident beams into optical fiber lines.

The hitherto known optical probes with a GRIN lens have the disadvantage that a separate beam deflection unit, such as a mirror or prism, is necessary for illuminating the measurement object.

Advantages of the invention The inventive optical probe or the device according to the invention with the probe has the advantage that the GRIN lens allows both the focusing of the input beam to a measuring beam and the deflection of the measuring beam to illuminate the measured object. Thus, at least two functions are advantageously ensured by a single optical element.

Consequently, there is no need to dispose a separate beam deflecting unit such as a prism next to the GRIN lens. The problem that results from this need is complex: First, even the production of such a prism is both financially and technically very complex. Their production takes several weeks, typically about 12 weeks. The main reason for this is the necessary compactness of the optical probe. Because if the probe is used for certain measurements e.g. into narrow bores, the probe must have the smallest possible diameter, and this also applies to all optical elements in the probe. Often, an edge length of less than 1 mm is required for a prism, which makes handling of the prism to be produced massively more difficult. With an edge length of about 0.8 mm, one finally reaches the technical limit. On the other hand, a very controlled grinding process on the prism is so important, because this the later angular accuracy of the reflective

Beam is determined.

But even after the laborious production of a very small prism remains the technical challenge to arrange this stable and accurate to the desired position in the probe. Typically, the prism is adhered to the focusing lens, often to the GRIN lens. Unfortunately, experience teaches that this step is not an easy task. In particular, it has been found that the required accuracy of the positioning of the prism on the lens can hardly be realized even under the highest demands. The angular accuracy of the positioning

Bonding process is about 20 times lower than the angular accuracy of the ground plasma itself. The disadvantages described above are abruptly eliminated by the probe according to the invention, since both the preparation of the prism and the assembly of the prism to the lens is unnecessary.

The advantage is achieved by an optical probe in which the GRIN lens has at least one surface inclined with respect to the direction of the input beam for deflecting the measuring beam.

Advantageous developments of the invention are specified in the subclaims and described in the description.

drawing

Embodiments of the invention will be explained in more detail with reference to the drawings and the description below. Show it:

FIG. 1 shows an example of a known probe from the prior art,

FIG. 2 shows an embodiment of a probe according to the invention,

3a shows a first embodiment of the GRIN lens, and

Figure 3b shows a second embodiment of the GRIN lens.

Description of the embodiments

FIG. 1 shows an example of an optical probe 1 known from the prior art. The structure of the known probe 1 has already been explained above.

A first embodiment of the probe according to the invention is shown in FIG. 2. As already known from the prior art and described above, FIG Probe 1 an input 10 for introducing an input beam into the probe 1, a GRIN lens 8 for focusing the input beam to a measuring beam and an output 20 for illuminating the measured objects to be tested. The input beam is introduced through an optical fiber 11 in the probe 1, wherein for the coupling of the optical fiber 11 in the probe 1, a ferrule 2 is provided. A spacer 4 "C" can be placed between the ferrule 2 and the GRIN lens 8. Such optical probes 1 are also called probe arms in certain applications because they optically scan measured objects, for example when scanning components of an automobile ,

The essential components of the probe 1 according to the invention include the input 10 for introducing an input beam into the probe 1, the GRIN lens 8 for focusing the input beam into a measuring beam and the output 20 for illuminating the test objects to be tested. According to the invention, it is further provided that the GRIN lens 8 has at least one surface 9 inclined with respect to the direction 7 of the input beam for deflecting the measuring beam. Since a beam is reflected on the inclined surface 9 and thereby deflected in a desired direction, a hitherto provided separate deflection unit such as a mirror or a prism is superfluous. The oblique surface necessary for the reflection is therefore already present in the GRIN lens 8.

Although in principle a plurality of inclined surfaces 9 on the GRIN lens are possible, in the exemplary embodiment of FIG. 2, the GRIN lens 8 has exactly one inclined surface 9. Thus, additional operations on the GRIN lens 8 are reduced as much as possible.

The GRIN lens 8 advantageously has a totally reflecting, inclined surface 9. Thus, no beam intensity is lost, but the entire beam intensity remains the measurement process.

It is best if the inclined surface 9 is arranged at the outlet 20 of the probe 1. This ensures direct illumination of the measurement objects. However, if desired, the inclined surface 9 may be slightly away from the exit 20 of the Probe 1 are arranged, for example, when a plurality of inclined surfaces 9 are provided on the GRIN lens 8, but fewer exits 20 of the probe 1. It is then to ensure by appropriate measures such as the arrangement of deflection that all measuring beams at the exit of the probe 1 can escape.

The inclined surface 9 may have an arbitrary inclination angle with respect to the direction 7 of the input beam as needed. However, practical inclination angles are 40 ° to 50 °, in particular 45 °.

Figures 3a and 3b show two variants of the GRIN lens 8 with a tilted

Surface 9, wherein in each case a lateral view and a top view of the GRIN lens 8 are shown. As can be seen from the drawings, the GRIN lens 8 in Fig. 3a has a circular shape in plan view. As a result, the measuring beam reflected at the inclined surface 9 is registered by the cylindrically curved outer surface. However, such a curved exit surface 15 for the measurement beam can be accepted if the measurement beam has, for example, a low beam diameter. Then namely the distortion of the measuring beam through the curved exit surface 15 is negligibly small. But in other applications, especially with a long working distance between the probe and the DUT, the effect of distortion may not be neglected.

In order to avoid such distortion by the cylindrical outer surface, a second variant of the GRIN lens 8 is proposed, as shown in FIG. 3b, according to which the GRIN lens 8 has a plane exit face 16 for the measuring beam. Since the exit surface 16 is flat, the measuring beam occurs almost perpendicular to

Lens surface and the effect of the distortion is almost completely eliminated. Thus, even with an otherwise curved outer shape of the GRIN lens 8, a sufficiently negligible distortion of the measuring beam can be ensured if a smooth outer shape is provided at least at the exit surface 16 for the measuring beam.

Incidentally, for all embodiments of the invention, the generation of the inclined surface 9 and / or the plane exit surface 16 on the GRIN lens 8 is simpler and more accurate than the production of the prisms of the prior art, because the GRIN lens 8 is typically larger than a prism in a same probe 1. The GRIN lens 8 is typically a few millimeters long. This considerably simplifies handling. It is proposed to grind and / or polish the GRIN lens 8 to produce the desired shapes. The inclined surface 9 and / or the flat exit surface 16 is then ground and / or polished after processing in the desired shape. In this grinding to obtain the inclined surface 9, a tapered end surface of the GRIN lens 8 is formed, so that two sides of different length are formed. These different sized side lengths lead to a path difference and thus influence the urspürngliche beam shape. To reduce this effect, a relatively low gradient refractive index material may be selected for the lens. The GRIN lens 8 thus produced would then be longer overall without this measure to compensate for the low gradient refractive index.

Advantageously, the inclined surface 9 and / or the flat exit surface 16 may be provided with a protective layer. These externally accessible surfaces are thus e.g. Specially protected against dirt.

Incidentally, the measurement beam reflected on the surface of the measurement object is picked up again by the probe 1. Typically, the reflected measuring beam now passes through the previous beam path in the opposite direction, i. it is reintroduced into the probe 1 at the exit 20 of the probe 1 and leaves the probe 1 at the entrance 10. The terms "input" and "output" do not refer to the reflected measuring beam as is familiar to a person skilled in the art. The measuring beam fed out again from the probe 1 is then fed to a detection unit to which an evaluation unit is connected. Thus, an analysis of the illuminated with the probe 1 measurement objects is possible.

Incidentally, all embodiments of the probe 1 described so far are suitable for being connected to a known interferometer. Together they then form a device for the interferometric measurement of measurement objects. Ideally, the interferometer is connected to the probe 1 by means of the already mentioned optical fiber 11. The construction of a typical Interferometers will not be further explained, since this has already been described in detail, for example, in the initially cited document DE 100 57 539 A1. It should only be emphasized that the interferometer can comprise an evaluation unit in addition to a detection unit.

In summary, it is stated that an optical probe 1 has been described in which the focusing lens 8 has at least one surface 9 inclined with respect to the direction 7 of the input beam for deflecting the measuring beam. This eliminates the need for a separate deflection unit such as a mirror or prism. Furthermore, a device has been proposed which comprises a per se known interferometer and the probe 1 described. Overall, this achieves a very simplified and precise production of an optical probe 1.

Claims

claims An optical probe (1) for optically examining targets, comprising an input (10) for introducing an input beam into the probe (1), a GRIN lens (8) (graduate index lens) for focusing the input beam into a measuring beam and an output (20) for illuminating the test objects to be tested, characterized in that the GRIN lens (8) has at least one opposite to the direction (7) of the input beam inclined surface (9) for deflecting the measuring beam. 2. probe (1) according to claim 1, dad urch in that the GRIN lens (8) has exactly one inclined surface (9). 3. probe (1) according to claim 1 or 2, dad urch in that the GRIN lens (8) has a totally reflecting, inclined surface (9). 4. probe (1) according to one of claims 1 to 3, dad urch in that the GRIN lens (8) has a plane exit surface (16) for the measuring beam. 5. probe (1) according to one of claims 1 to 4, dad urch in that the inclined surface (9) and / or the plane exit surface (16) is ground and / or polished. 6. probe (1) according to one of claims 1 to 5, dad urch in that the inclined surface (9) and / or the flat exit surface (16) is provided with a protective layer. 7. probe (1) according to one of claims 1 to 6, characterized in that the inclined surface (9) at the output (20) of the probe (1) is arranged. 8. probe (1) according to one of claims 1 to 7, characterized in that the inclined surface (9) has an inclination angle relative to the direction (7) of the input beam of 40 ° to 50 °, in particular 45 °. 9. An apparatus for interferometric measurement of measurement objects, wherein a Interferometer is connected to a probe (1) according to one of claims 1 to 8. 10. The device according to claim 9, characterized in that the interferometer with the probe (1) by means of an optical fiber (11) is connected.