DE8814391U1 - Reflector assembly for Michelson interferometer - Google Patents

Description

48 367 &zgr;-£5

Reflector assembly for Michelson interferometer DESCRIPTION

The invention relates to a reflector assembly for Michelson interferometers with a beam splitter arranged in the measuring beam path, which divides the measuring beam path into two partial beam paths, with a first mirror arrangement reflecting parallel to the incident beam in each partial beam path and with at least one second mirror reflecting parallel to the incident beam, which is arranged in the beam path reflected by one of the first mirror arrangements and is connected to the beam splitter.

Such reflector assemblies for Michelson interferometers are known, e.g. from DE 30 05 520 C2. In the arrangement disclosed there, the beam splitter and the second mirror are structurally separate from one another.

Furthermore, in the publication "IEEE Transactions on Geoscience and Remote Sensing", Vol. GE-21, No. 3, pages 345 to 349, published on July 3, 1983, a Michelson interfereometer is described in which the beam splitter is formed by two glass prisms cemented together, on whose hypotenuse surfaces a measuring beam is divided and then recombined, and the second mirror or mirrors are attached to the cathetial surfaces of these prisms.

With such systems, the problem always arises of different temperature conditions in the interferometer

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as far as possible in order to achieve the highest possible degree of modulation. As is well known, the degree of modulation M is expressed by the relationship M =■ ¹ M^ ¹ DC, where I» is the modulated intensity and Ij _x , is the reflected light intensity. The theoretically conceivable value M=I is not reached in practice; the practically achievable values for M are between 0.5 and 0.8.

In order to minimize the impairment of the degree of modulation, interferometers are often thermostatted, i.e. they are placed in arrangements in which the highest possible temperature constancy with the most even temperature distribution is sought. In practice, however, even such systems reach their limits, since the temperature control is restricted to the temperature conditions at certain points or in certain narrow sub-areas within the instrument, whereby certain temperature differences within the instrument cannot usually be completely eliminated. On the other hand, the technical effort required for thermostatting the instrument is not insignificant, which noticeably increases the costs of production and operation.

The invention is based on the object of creating a reflector assembly for a Michelson interferometer in which the temperature sensitivity is reduced.

According to the invention, this is achieved in a reflector assembly of the type mentioned above by a partially transparent reflector serving as a beam splitter and the

second mirrors are arranged on a common carrier.

This reduces the temperature sensitivity of the assembly in a surprisingly simple way, which is why a high degree of modulation is achieved even without thermostatting. It has been shown that with the reflector assembly according to the invention, the degree of modulation of the interferometer changes by less than 1% per degree, whereas with previous designs changes of 5% per degree or even greater changes had to be accepted. Nevertheless, with the design according to the invention , the production and operating costs for the interferometer can be kept low by omitting thermostatting.

Further embodiments of the invention emerge from the claims subordinate to claim 1.

An embodiment of the invention is described below with reference to

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Fig. 1 a Michelson double pendulum interferometer in systematic representation and

Fig. 2 shows an embodiment of the reflector system contained in Fig. 1 in an enlarged, perspective view.

In Fig. 1, a Michelson double pendulum interferometer is shown which, within an instrument housing or frame (not shown), has a cross-sectional

rectangular or square carrier L for the reflector assembly described in more detail below. A surface 2 is arranged within this carrier, on which a semi-transparent reflector 3 serving as a beam splitter is arranged in a manner described in more detail below. In the described embodiment, this is inclined to the beam path 4 of the incident measuring light at an angle of 45° and divides the measuring light beam path into the two partial beam paths 5 and 6.

A double pendulum 8 is rotatable about an axis 7 mounted on the housing or frame of the interferometer (not shown). The double pendulum 8 has two pendulum arms 9, 10 that protrude at right angles. Each of these pendulum arms carries a first mirror arrangement that reflects the incident beam parallel to it, which in the described embodiment is designed as a roof edge reflector with reflector elements 11a, 11b or 12a, 12b that abut one another at right angles along a roof edge. The

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the partial beam path 5 or 6 of the measuring light and reflects it to the reflector element 11b or 12b, from where the partial beam path 5 or 6 emerges as a laterally offset beam path 5' or 6' parallel to the incident beam path and strikes a second mirror 13 or 14, respectively, which reflects the incident beam parallel to it. The two second mirrors 13, 14 are arranged on the carrier I, as will be explained in more detail below.

The mirrors 13, 14 reflecting the beam parallel to it reflect the rays of the beam paths 5' and 6' that impinge on them back into themselves to the roof edge reflectors 11a, 11b and 12a, 12b, respectively, where they are laterally set back and along the beam paths 5 and 6 of the incident partial beam paths 5, 6 on the partially transparent reflector 3 of the carrier.

collecting lens 16 to a detector 17, which carries out the interferometric evaluation.

The first mirror arrangements described above, which reflect the incident beam parallel to it, can be designed as triple mirrors in the form of a so-called cube corner instead of as roof edge mirrors.

The structure of a preferred embodiment of the carrier 1 for the partially transparent reflector 3 and for the second mirrors 13 and 14 of the reflector assembly will now be described in more detail with reference to Fig. 2.

The carrier 1 has a square lower plate 18 and a parallel, identically designed upper plate 19, to which the side walls 20, 21 are attached along two sides, which abut one another at right angles in the described embodiment and protrude beyond the upper plate 19. The parts 18, 19, 20, 21 together partially form a cuboid or cube-shaped framework.

The angle between the two side walls 20, 21 and the geometric shape of the frame formed by the carrier 1 depend on the design of the interferometer.

The specified angle can also take on values other than 90".

Between the parallel lower and upper plates 18, 19 a diagonal wall 22 runs along the diagonal surface 2. In a circular cutout 23 of the same is located the partially transparent reflector 3, while the

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Mirrors 13, 14 are mounted on the protruding parts of the side walls 20, 21.

In the embodiment according to Fig. 2, the mirrors 13, 14 are arranged above the partially transparent reflector 3, which acts as a beam splitter. They can also be arranged laterally thereto, as is shown in principle in Fig. 1.

The spatially compact arrangement of the partially transparent reflector 3 acting as a beam splitter and the second mirrors 13, 14 on the common carrier 1 ensures that these components of the interferometer have largely identical temperature values, which significantly reduces the temperature sensitivity of the system.

To further reduce temperature differences, the carrier 1 is expediently made of aluminum, since this material has a high thermal conductivity. In the interest of good conductivity, the carrier 1 consisting of the walls 18, 19, 20, 21 and 22 can preferably be formed in one piece, e.g. as

The beam splitter 3, designed as a partially transparent reflector, can preferably be made of KBr, ZnS, ZnSe, CaF, Ge or Si.

Claims (7)

PROTECTION CLAIMS 1. Reflector assembly for Michelson interferometers with a beam splitter arranged in the measuring beam path, which divides the measuring beam path into two partial beam paths, with a first mirror arrangement reflecting parallel to the incident beam in each partial beam path and with at least one second mirror reflecting parallel to the incident beam, which is arranged in the beam path reflected by one of the first mirror arrangements and is connected to the beam splitter, characterized in that a partially transparent reflector (3) serving as a beam splitter and the second mirror (13; 14) are arranged on a common carrier (1). 2. Reflector assembly according to claim 1, characterized in that two second mirrors (13, 14) are arranged on the carrier (1), each of which is exposed to a beam path reflected by the first mirror arrangements (11, 11b; 12a, 12b). 3. Reflector assembly according to claim 1 or 2, characterized in that the carrier (1) at least partially has a cuboid-shaped framework, the partially transparent reflector (3) being arranged on a diagonally arranged wall (2) of the cuboid shape and the second mirror or mirrors (13, 14) being arranged on side walls (20, 21) of the cuboid shape or on extensions of these side walls. 4. Reflector assembly according to claim 3, characterized in that the two second "; Mirrors (13, 14) on two angularly adjoining f| side walls (20, 21) of the cuboid shape or . extensions of these side walls are arranged. 5. Reflector assembly according to one of the preceding claims, characterized in that the carrier (1) consists of aluminum. 6. Reflector assembly according to one of the preceding claims, characterized in that the carrier (1) is formed in one piece. 7. Reflector assembly according to one of the preceding claims, characterized in that the partially transparent reflector (3) is made of KBr, ZnS, ZnI, CaF, Ge or Si.