JP2006284233A - Apparatus for measuring system error and interferometer system for wavefront measurement equipped with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a apparatus for measuring a system error provided capable of measuring a system error in an interferometer for wavefront measurements easily with high precision, and also to provide an interferometer system for wavefront measurement equipped with a system error measuring apparatus like this. <P>SOLUTION: The system error measuring apparatus is equipped with an optical unit 2 to be installed on a photoconducting path for luminous flux to be inspected, on the occasion of measuring the system error of the interferometer 3 for wavefront measurements. This optical unit 2 is provided with a convergence optical system 21 which outputs incident luminous flux as converged luminous flux, a penetrate type pinhole 22 which shapes the wavefront of the converged luminous flux from the converging system 21 and makes it into diverging luminous flux and outputs it, and an output optical system 24 which converts the diverging luminous flux from the pinhole 22 into evaluating luminous flux capable of measuring the system error of the interferometer 3, and outputs it. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention includes a system error measurement device for measuring a system error in a wavefront measurement interferometer that performs wavefront measurement of a test light beam at the time of product shipment, maintenance, and the like, and such a system error measurement device. The present invention relates to a wavefront measuring interferometer apparatus.

  Conventionally, wavefront measurement of a test light beam is performed based on interference fringes obtained by separating a test light beam, which is an object of wavefront measurement, into two light beams, shaping one light beam and then interfering with the other light beam. Interferometers for wavefront measurement are known. As this type of interferometer, an interferometer having a Mach-Zehnder type interference optical system in which two light beams to be interfered pass through different optical paths has been generally used. By using a wavefront shaping means by a pinhole, an interferometer device for wavefront measurement has been devised that makes it possible to adopt a Fizeau-type interference optical system in which two light beams to be interfered pass along one optical axis, It has already been disclosed to the Patent Office (see Patent Documents 1 and 2 below).

  In recent years, such wavefront measurement interferometers have been required to have a measurement accuracy as high as several tenths of the wavelength of the light beam to be measured. For this reason, due to the influence of aberration, vibration, etc. of individual optical members. Efforts have been made to eliminate generated system errors as much as possible by using high-performance optical members or by constructing the optical system robustly.

  However, it is technically very difficult to completely eliminate such system errors. Therefore, generally, system errors that cannot be removed are measured in advance, and these system errors are calculated from the analysis results of wavefront measurements. It is designed to be removed arithmetically.

  As a method for measuring such a system error, an evaluation light beam having an ideal wavefront capable of evaluating aberrations of an optical member is generated, and this evaluation light beam is regarded as a test light beam to be measured. A method for measuring the wavefront is known. In other words, when there is no system error and the wavefront of the evaluation light beam is perfect, the interference fringes obtained by this measurement become so-called perfect null fringes. The system error is obtained by comparing the interference fringes that are generated with the null fringes.

Japanese Patent Application No. 2004-168965 Specification Japanese Patent Application No. 2004-168966

  Conventionally, an evaluation light beam necessary for measuring a system error is generated using a spherical wave obtained by irradiating a laser beam or the like onto a spherical mirror polished with high accuracy.

  However, since the surface accuracy of a spherical mirror is only a few tenths of the wavelength of light even with high accuracy, a wavefront that requires the same high measurement accuracy is required for a light beam generated using such a spherical mirror. There is a problem that it is insufficient as a light beam for evaluation of a measurement interferometer, and it is difficult to measure a system error with high accuracy.

  In addition, a separate light source with high wavefront accuracy for irradiating the spherical mirror is required, and in order to convert the spherical wave obtained by the spherical mirror into a luminous flux for evaluation and guide it to the system, the alignment of the spherical mirror and the light source must be increased. It is necessary to adjust to accuracy. For this reason, the procedure required for measuring the system error is complicated, and there is a problem that it takes a lot of time for the measurement.

  The present invention has been made in view of such circumstances, and provides a system error measurement device capable of easily and accurately measuring a system error in a wavefront measurement interferometer, and such a system error measurement device. It is an object of the present invention to provide a wavefront measuring interferometer apparatus.

  In order to achieve the above object, in the present invention, an optical unit for wavefront shaping by a transmission type pinhole is arranged on a light guide path of a test light beam when measuring a system error.

That is, the system error measuring apparatus according to the present invention is disposed on the light guide path of the test light beam, and separates the light beam guided on the light guide path into two, and the light beam separation means separates the light beam. Wavefront shaping means for wavefront shaping one of the light fluxes to be a reference light flux, and interfering the reference light flux from the wavefront shaping means with the other light flux separated by the light flux separation means to obtain wavefront information of the light flux. In an apparatus for measuring a system error in a wavefront measurement interferometer having an interference fringe acquisition means for obtaining a supported interference fringe,
An optical unit disposed on the light guide when measuring the system error,
A converging optical system that outputs an incident light beam as a convergent light beam;
A transmissive pinhole arranged at a substantially converging point of the convergent light beam from the converging optical system, and shaping the incident convergent light beam into a wavefront and outputting it as a divergent light beam;
An output optical system that outputs the divergent light beam from the transmissive pinhole as an evaluation light beam capable of measuring the system error of the wavefront measurement interferometer and outputs the light beam to the light beam separation unit;
Is provided with an optical unit.

  In the system error measuring apparatus according to the present invention, the wavefront information of the evaluation light beam and the wavefront measuring interferometer system obtained by the wavefront measuring interferometer when the optical unit is disposed on the light guide. It is possible to provide a system error analysis means for analyzing the interference fringes carrying the error information and obtaining the system error.

  Further, the wavefront measuring interferometer device according to the present invention is arranged on a light guide path of a test light beam, and separates the light beam guided onto the light guide path into two, and the light beam separation means. Wavefront shaping means for wavefront shaping one of the light fluxes separated by step (1) into a reference light flux, and interfering the reference light flux from the wavefront shaping means with the other light flux separated by the light flux separation means for wavefront of the light flux A wavefront measurement interferometer having an interference fringe acquisition means for obtaining an interference fringe carrying information, comprising the system error measuring device according to the present invention.

  The wavefront shaping means is arranged at a converging lens for converging the one light beam and a substantially converging point of the one light beam by the converging lens, and reflects the incident one light beam into a reference light beam by shaping the wavefront. And a mold pinhole.

  The “transmission type pinhole” is determined by the diffraction limit of the convergent light beam incident on the transmission type pinhole (preferably configured to be smaller than the diffraction limit), and at least a part of the convergent light beam. Has a function of transmitting (passing) as an ideal spherical wave wave-shaped.

  The “reflective pinhole” is determined by the diffraction limit of the convergent light beam incident on the reflective pinhole (preferably configured to be smaller than the diffraction limit), and at least a part of the convergent light beam. That has a function of reflecting as an ideal spherical wave wavefront-shaped. As such a reflection type pinhole, it is possible to use those of various configurations, but as a specific aspect, for example, a microreflection region formed on a substrate, or a microneedle at the tip of a needle-like member Examples thereof include those in which a reflective region is formed, or those in which a reflective surface is disposed in the immediate vicinity of the back side of a normal pinhole.

  The system error measuring apparatus according to the present invention includes the optical unit arranged on the light guide path of the light beam to be measured when measuring the system error, and thus has the following effects.

  That is, according to this optical unit, by using a transmissive pinhole, it is possible to output the evaluation light beam whose wavefront is accurately shaped to the order of several thousandths of the wavelength of the incident light beam. It becomes possible to measure the system error of the interferometer for wavefront measurement with high accuracy. In addition, since this optical unit can be easily arranged on the light guide path of the test light beam, the system error of the wavefront measuring interferometer can be easily and quickly performed.

  In addition, according to the interferometer device for wavefront measurement according to the present invention, since the system error measurement device according to the present invention is provided, the system error can be measured easily and in a short time. Even when the system error changes due to the above, it is possible to easily calibrate such a system error.

  Hereinafter, embodiments according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram schematically showing a wavefront measuring interferometer device according to an embodiment of the present invention.

<Configuration of interferometer for wavefront measurement>
The wavefront measurement interferometer device shown in FIG. 1 measures the wavefront of the test light beam output from the test light source device 1 and is installed on the light guide path of the test light beam at the time of system error measurement described later. Optical unit 2, wavefront measurement interferometer 3 having a Michelson-type optical system arrangement, and analysis unit 4 for performing fringe analysis and the like.

  The test light source device 1 includes, for example, a light source 11 such as a semiconductor laser, a collimator lens 12 that converts a divergent light beam from the light source 11 into a parallel light beam, and a reflection mirror 13. It is assumed to be configured to output. Such an LD light beam for optical pickup may be used with harmonics superimposed to shorten the coherence distance. In the wavefront measurement interferometer apparatus shown in FIG. Even when the coherent LD light beam is used as the test light beam, the wavefront measurement can be performed. The test light source device 1 is used by being incorporated in an optical pickup device or the like, and is not a component of the wavefront measuring interferometer device.

  On the other hand, the optical unit 2 which is a constituent element of the wavefront measuring interferometer device includes a converging optical system 21 that outputs an incident light beam as a convergent light beam, and a substantially converging point of the convergent light beam from the converging optical system 21. A transmissive pinhole 22 formed in the pinhole plate 23, the size of which is preferably determined by the diffraction limit of the incident light beam. Output optics which converts the divergent light beam from the transmissive pinhole 22 into an evaluation light beam which is a parallel light beam capable of measuring the system error of the wavefront measuring interferometer 3 and outputs the converted light beam. The system 24 is held in a lens barrel (not shown). As described above, the optical unit 2 is installed on the light guide path of the test light beam when measuring the system error of the wavefront measurement interferometer 3. When done, it is retracted from the light guide. In FIG. 1, the converging optical system 21 and the output optical system 23 are simply illustrated as being composed of one lens, but there are cases where these are composed of a plurality of optical elements.

  On the other hand, the wavefront measuring interferometer 3 is disposed on the light guide path of the test light beam, and separates the light beam guided on the light guide path into two, and the light beam separation means. Wavefront shaping means (32, 34) for wavefront shaping one of the light fluxes separated by the above to become a reference light flux, and interfering the reference light flux from the wavefront shaping means with the other light flux separated by the light flux separation means, Interference fringe acquisition means (31, 36 to 38) for obtaining interference fringes carrying the wavefront information of the luminous flux.

  In the present embodiment, the light beam separating means is constituted by a beam splitter having a light beam separating / combining surface 31, and the wavefront shaping means converges the one light beam separated by the light beam separating means. And a reflection type pinhole 34 which is disposed at a substantially convergent point of one light beam by the converging lens 32 and which wave-shapes the incident one light beam to become the reference light beam.

  Further, the reflection type pinhole 34 is made of a metal film such as gold, aluminum, or chromium formed on the substrate surface 35 formed of a curved surface by, for example, vapor deposition, and the size thereof is preferably incident. Therefore, it is configured to be smaller than the diffraction limit of the one light beam. Then, at least a part of the one light beam incident from the left in the figure is wavefront shaped to form a reference light beam, and the reference light beam is output toward the convergent lens 32. The substrate surface 35 is subjected to an antireflection coating, and a window 33a through which the one light flux and the reference light flux pass is provided between the converging lens 32 and the reflective pinhole 34. A shading plate 33 is disposed.

  In the present embodiment, the interference fringe acquisition means includes a reflection plate 36 having a reflection surface 36a that reflects the other light beam separated by the light beam separation means, and the other light beam reflected from the reflection surface 36a. Is composed of the light beam separation / combination surface 31 that combines and interferes with the reference light beam, an imaging lens 37 that forms an interference fringe obtained by the interference, and an imaging camera 38 that images the interference fringe. Has been. The optical path length from the light beam separation / combining surface 31 to the light beam separation / combining surface 31 through the reflective pinhole 34 so that interference fringes can be obtained even when the test light beam is a low coherence light beam. And the optical path length from the light beam separation / combination surface 31 through the reflection surface 36a to the light beam separation / combination surface 31 are adjusted so as to substantially match each other. The reflection plate 36 includes a mechanism for moving the reflection plate 36 in the optical axis direction in order to perform such optical path length adjustment, and a mechanism for finely moving the reflection plate 36 in the optical axis direction when performing fringe scan measurement. (All are not shown).

  The analysis unit 4 includes a fringe analysis device 41 that performs image processing and fringe analysis, an input device 42 such as a keyboard, and a display device 43. The fringe analysis device 41 is configured by a computer or the like, and includes a storage unit that stores a program for performing image processing and fringe analysis, an arithmetic unit that executes a program and performs various calculations, and the like. It is possible to analyze the state of the wavefront of the test light beam based on the interference fringes imaged in FIG.

  Further, in the fringe analyzer 41, the measured value of the system error of the wavefront measuring interferometer 3 measured in advance is stored in a memory or the like, and the measured value of the system error is calculated from the analysis result of the wavefront measurement. Configured to remove.

  When performing wavefront measurement in the present embodiment, the optical unit 2 is retracted from the light guide path of the test light beam, and the test light beam output from the test light source device 1 passes along the light guide path. The light enters the separation / multiplexing surface 31.

  The test light beam incident on the light beam separation / combination surface 31 is divided into a first light beam that passes through the light beam separation / combination surface 31 and a second light beam that is reflected upward in the drawing at the light beam separation / combination surface 31. The separated first light beam is incident on the reflection type pinhole 34 through the converging lens 32, where the wavefront is shaped and reflected as a reference light beam, and returns to the light beam separation / combining surface 31 through the converging lens 32 again.

  On the other hand, the second light beam is reflected by the reflecting surface 36a of the reflecting plate 36 and returns to the light beam separation / combining surface 31, where it is combined with the reference light beam to be interference light. This interference light is taken into the imaging camera 38 through the imaging lens 37, and an interference fringe carrying the wavefront information of the test light beam is imaged there.

  The captured interference fringes are subjected to arithmetic processing or the like based on a predetermined fringe analysis program in the fringe analysis device 41, and the wavefront state of the test light beam is analyzed. In this analysis, the system error (value measured in advance) of the wavefront measurement interferometer 3 is arithmetically removed from the analysis result of the wavefront measurement.

<Configuration of system error measurement device>
Next, a system error measurement device according to an embodiment of the present invention will be described. As described above, the optical unit 2 and the fringe analyzer 41 that constitute a part of the wavefront measuring interferometer shown in FIG. 1 also constitute a system error measuring device according to an embodiment of the present invention.

  That is, the system error measurement device of the present embodiment includes the optical unit 2 and the fringe analysis device 41. When the optical unit 2 is disposed on the light guide path of the test light beam, System error analysis obtained by analyzing the interference fringes carrying the wavefront information of the evaluation light flux and the system error of the wavefront measurement interferometer obtained by the wavefront measurement interferometer 3, and obtaining a new measurement value of the system error Means are provided as a program or the like stored in a memory or the like. Whether or not a change has occurred in the measured value of the system error of the wavefront measuring interferometer 3 by comparing the obtained new measured value of the system error with the original measured value that has been measured in advance. When the change occurs, the measured value is calibrated.

<Measurement of system error>
In the present embodiment, when measuring the system error of the wavefront measuring interferometer 3, the optical unit 2 is installed on the light guide path of the test light beam, and a predetermined light source (the test light source device 1 may be used). The parallel light beam output from (Yes) enters the optical unit 2 along the light guide path.

  The light beam incident on the optical unit 2 is converged by the converging optical system 21 and then incident on the transmissive pinhole 22 disposed at the substantially converging point. At least a part of the incident convergent light beam is wavefront shaped in the transmission pinhole 22 and is emitted toward the output optical system 24 as a divergent light beam. The divergent light beam incident on the output optical system 24 is converted into a parallel light beam and is incident on the light beam separation / combining surface 31 as an evaluation light beam.

  The evaluation light beam incident on the light beam separation / combination surface 31 is separated into two at the light beam separation / combination surface 31, one of which returns to the light beam separation / combination surface 31 through the wavefront shaping means, and the other is the reflector. The light is reflected by the reflecting surface 36a of 36 and returns to the light beam separation / combining surface 31, where they are combined.

  The interference light obtained by this multiplexing is taken into the imaging camera 38 through the imaging lens 37, where the interference fringes carrying the wavefront information of the evaluation light beam and the system error information of the wavefront measurement interferometer 3 are imaged. .

  Since the evaluation light beam is wavefront shaped with high accuracy by the optical unit 2, if there is no system error of the wavefront measurement interferometer 3, the imaged interference fringe is in a null fringe state. On the other hand, when there is a system error, the obtained interference fringes are not in the null fringe state. Therefore, the fringe analysis device 41 compares the actually obtained interference fringes with the null fringes to obtain a wavefront measurement interferometer. A new measurement value of system error 3 is obtained.

  The newly obtained measurement value of the system error is compared with the original measurement value stored in advance in the fringe analysis apparatus 41, thereby determining whether or not a change has occurred in the system error. If it is determined that the error has occurred, the original measurement value is calibrated and the new measurement value is stored in a memory or the like.

  As described above, according to the system error measuring apparatus according to the present embodiment, the measurement and calibration of the system error of the wavefront measuring interferometer 3 can be performed by arranging the optical unit 2 on the light guide path of the test light beam. It can be carried out easily and in a short time.

  In addition, since the optical unit 2 performs wavefront shaping of the incident light beam by the transmission type pinhole 22, it is possible to output the evaluation light beam that has been wavefront shaped with high accuracy up to an order of several thousandth of the wavelength. Compared to the conventional technique of wavefront shaping using a spherical mirror, the system error of the wavefront measuring interferometer 3 can be measured with high accuracy.

  In addition, according to the wavefront measurement interferometer apparatus according to this embodiment, the system error measurement apparatus according to the present invention is provided, so that the measurement of the system error of the wavefront measurement interferometer 3 can be performed with high accuracy and in a short time. Therefore, even if the system error changes due to use over time, it can be easily calibrated. In addition, by appropriately calibrating the system error, it is possible to maintain a state where highly accurate wavefront measurement can be performed.

<Change of mode>
As mentioned above, although one Embodiment of this invention was described, this invention is not restricted to the said embodiment, A mode can be variously changed.

  For example, in the above embodiment, the optical unit 2 and the fringe analyzer 41 that constitute the system error measuring device also constitute a part of the wavefront measuring interferometer device. You may make it comprise separately from the interferometer apparatus for wavefront measurement.

  In the above embodiment, the wavefront measuring interferometer 3 has a Michelson type optical system arrangement, but the present invention is applicable to various wavefront measuring interferometers such as a Mach-Zehnder type and a Fizeau type. Is possible.

  In the above-described embodiment, the semiconductor laser beam on which harmonics are superimposed is exemplified as a test beam having a short coherence distance. However, a general low-light such as an LED, SLD, halogen lamp, high-pressure mercury lamp, or the like is used. The light beam output from the coherent light source can be used as the test light beam. Of course, a light beam having a long coherence distance, such as a general laser light beam, can be used as a test light beam.

  The present invention can also be applied to a measuring apparatus disclosed in the above-mentioned Patent Document 2 that can simultaneously perform the wavefront measurement of the test light beam and the characteristic measurement of the light beam spot.

1 is a schematic configuration diagram of an interferometer device for wavefront measurement according to an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Test light source apparatus 2 Optical unit 3 Interferometer for wavefront measurement 4 Analysis part 11 Light source 12 Collimator lens 13 Reflection mirror 21 Convergence optical system 22 Transmission type pinhole 23 Pinhole plate 24 Output optical system 31 Light beam separation / combining surface 32 Convergence Lens 33 Light-shielding plate 33a Window portion 34 Reflective pinhole 35 Substrate surface 36 Reflector plate 36a Reflective surface 37 Imaging lens 38 Imaging camera 41 Stripe analysis device 42 Input device 43 Display device

Claims (4)

A light beam separating unit that is disposed on the light guide path of the test light beam and separates the light beam guided onto the light guide path into two parts, and a reference light beam obtained by wavefront shaping one of the light beams separated by the light beam separating unit. An interference fringe acquisition unit that obtains an interference fringe carrying the wavefront information of the light beam by causing the reference light beam from the wavefront shaping unit to interfere with the other light beam separated by the light beam separation unit; In an apparatus for measuring a system error in an interferometer for wavefront measurement having
An optical unit disposed on the light guide when measuring the system error,
A converging optical system that outputs an incident light beam as a convergent light beam;
A transmissive pinhole arranged at a substantially converging point of the convergent light beam from the converging optical system, and shaping the incident convergent light beam into a wavefront and outputting it as a divergent light beam;
An output optical system that outputs the divergent light beam from the transmissive pinhole as an evaluation light beam capable of measuring the system error of the wavefront measurement interferometer and outputs the evaluation light beam to the light beam separation unit. An optical unit,
A system error measuring device comprising:   Interference fringes carrying the wavefront information of the evaluation light beam and the system error of the wavefront measurement interferometer obtained by the wavefront measurement interferometer when the optical unit is disposed on the light guide. The system error measuring device according to claim 1, further comprising system error analyzing means for analyzing and obtaining the system error. A light beam separating unit that is disposed on the light guide path of the test light beam and separates the light beam guided onto the light guide path into two parts, and a reference light beam obtained by wavefront shaping one of the light beams separated by the light beam separating unit. An interference fringe acquisition unit that obtains an interference fringe carrying the wavefront information of the light beam by causing the reference light beam from the wavefront shaping unit to interfere with the other light beam separated by the light beam separation unit; In a wavefront measuring interferometer having
An interferometer apparatus for wavefront measurement, comprising the system error measurement apparatus according to claim 1. The wavefront shaping means is arranged at a converging lens for converging the one light beam and a substantially converging point of the one light beam by the converging lens, and reflects the incident one light beam into a reference light beam by shaping the wavefront of the one light beam. 4. The wavefront measuring interferometer device according to claim 3, wherein the wavefront measuring interferometer device comprises a pinhole.

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