JP4878229B2 - Interference fringe analysis method and aberration measurement method of optical element - Google Patents

Description

The present invention relates to an interference fringe analysis method and an aberration measurement method for lenses and other optical elements.

As an interference fringe analysis method or aberration measurement method for an optical element, a reference wavefront having a spatial carrier generated by tilting the reference surface with respect to the optical axis of the interferometer (hereinafter referred to as the optical axis) and an optical axis approximately There is a so-called spatial phase shift method (hereinafter referred to as a spatial phase shift method) in which interference fringes formed by a vertical wavefront to be detected are analyzed and aberrations are measured thereby. In the spatial phase shift method, not only can the interference fringe analysis be performed with high accuracy by obtaining the wavefront aberration of the optical element, but also the reference surface and the test surface can be compared with the temporal phase shift method (fringe scan method). Therefore, the interference fringe analysis can be performed at a low cost and in a short time.

On the other hand, in recent years, there has been a demand for an optical element having a wavefront aberration level performance over multiple wavelengths. In such interference fringe analysis of optical elements, a multi-wavelength interferometer that can emit light of multiple wavelengths may be used, and the accuracy of the analysis also in interference fringe analysis or aberration measurement using a multi-wavelength interferometer In consideration of cost and efficiency, a spatial phase shift method is used.
JP-A-1-185404

However, when the interference fringe analysis is performed by the spatial phase shift method while changing the wavelength of the light source in the multiwavelength interferometer, the spatial carrier is modulated according to the wavelength of the light source. In other words, the interval between the stripes of the tilt stripe varies depending on the wavelength of the light source, and as a result, the frequency also varies. Conventionally, by utilizing the fact that the spatial carrier changes according to the inclination angle of the reference surface, the inclination angle of the reference surface is appropriately changed every time the wavelength of the light source is changed to support the modulation of the spatial carrier. . However, it takes a lot of time to fine-tune the tilt angle of the reference surface so as to suppress the modulation of the spatial carrier with high accuracy. Furthermore, in order to fine-tune the tilt angle of the reference surface quickly, An expensive stage device capable of high-precision and high-speed driving is required, and further, the measurement state when the wavelength is changed (hereinafter referred to as measurement alignment) is changed by mechanical adjustment. There was a problem that the measurement alignment could not be maintained before and after changing the wavelength. Therefore, it is difficult to accurately perform interference fringe analysis of optical elements over multiple wavelengths.

In order to solve the above-described problem, in the interference fringe analysis method of the present invention, in order to perform interference fringe analysis using a spatial carrier, a tilt interference fringe frequency setting for setting a frequency of a tilt interference fringe as an interference fringe analysis parameter is performed. A tilt interference fringe forming step of causing a reference wavefront from an inclined reference plane and a test wavefront from the test surface to interfere with each other in the interferometer to form a tilt interference fringe in which spatial carriers are superimposed; and tilt interference The tilt interference fringe alignment step for tilting the reference surface so that the frequency set in the fringe frequency setting step is equal to the frequency of the tilt interference fringe formed in the tilt interference fringe formation step, and the light source wavelength of the interferometer if you change, instead of the frequency of the tilt fringes set at tilt fringe frequency setting step, variable A tilt fringe frequency calculating step of calculating a frequency of tilt fringes in accordance with a further light sources wavelength, when tilt interference fringes formed by the tilt fringe forming step, changing the light source wavelength of the interferometer, are interference fringe analysis using the frequency of the tilt fringes calculated in tilt fringe frequency calculation step, if it does not change the light source wavelength of the interferometer, using a frequency of tilt fringes set at tilt fringe frequency setting step An interference fringe analysis step for analyzing the interference fringes.

In the aberration measurement method of the present invention, in order to perform interference fringe analysis using a spatial carrier, a tilt interference fringe frequency setting step for setting a tilt interference fringe frequency as an interference fringe analysis parameter is tilted in an interferometer. A reference wavefront from the reference surface and a test wavefront from the test surface interfere with each other, a tilt interference fringe forming step for forming a tilt interference fringe on which spatial carriers are superimposed, and a frequency set in the tilt interference fringe frequency setting step. The tilt interference fringe frequency setting is performed when the tilt interference fringe alignment step in which the reference plane is inclined so that the frequency of the tilt interference fringe formed in the tilt interference fringe forming step is equal, and the light source wavelength of the interferometer is changed. Instead of the tilt interference fringe frequency set in step, til according to the changed light source wavelength a tilt interference fringe frequency calculating step for calculating a frequency of t interference fringes ;
tilt fringe, when you change the light source wavelength of the interferometer, if the interference fringe analysis using the frequency of the tilt fringes calculated in tilt fringe frequency calculation step, without changing the light source wavelength of the interferometer An aberration measurement step in which interference fringe analysis is performed using the frequency of the tilt interference fringe set in the tilt interference fringe frequency setting step, and the aberration is measured based on one of the analysis results.

  According to the present invention, when the interference fringe analysis is performed by the spatial phase shift method while changing the wavelength of the light source, the tilt interference fringe, which is a parameter for interference fringe analysis, according to the wavelength of the light source (interferometer wavelength). The spatial phase corresponding to modulation of the spatial carrier by changing the wavelength of the interferometer light source at high speed and low cost by calculating the frequency (hereinafter referred to as analysis frequency) and analyzing the interference fringes using the calculated value Interference fringe analysis and aberration measurement can be performed by the shift method. Furthermore, interference fringe analysis and aberration measurement by the spatial phase shift method can be performed without changing the measurement alignment at all.

  Hereinafter, embodiments according to the present invention will be described in detail with reference to the drawings. In the present embodiment, the test lens 80 is an object of interference fringe analysis and aberration measurement, but the present invention can also be applied to other optical elements.

  The interference fringe analysis apparatus used for the interference fringe analysis method and the aberration measurement method according to the present embodiment includes an interference fringe forming unit 20 and an interference fringe analysis unit 42, as shown in FIG.

  The interference fringe forming unit 20 can use a known multi-wavelength interferometer. In this embodiment, as shown in FIG. 1, a semiconductor laser (LD) (light source) 21 and an interference fringe observation CCD (charge coupled device) are used. ) 41 and an optical system 30 are used. Here, the optical system 30 includes a collimator lens 31, a mirror 32, a half mirror 34, a condenser lens 35, a reference plane plate 36, a pinhole 37, and a reflection reference concave mirror 38.

The semiconductor laser 21 is driven by a driver 22 and emits a predetermined laser beam as a light source (hereinafter referred to as reference light) of an interferometer. The driver 22 supplies a drive current to the semiconductor laser 21 based on a control signal output from the control unit 43 connected thereto. The control unit 43 outputs a control signal corresponding to the wavelength of the reference light input from the input unit 45 and other information, and the semiconductor laser 21 emits reference light having a plurality of types of wavelengths in response to the control signal. be able to. In the traveling direction of the laser light emitted from the semiconductor laser 21, a collimator lens 31 and a mirror 32 are arranged in order from the semiconductor laser 21 side. Laser light emitted from the semiconductor laser 21 is collimated by a collimator lens 31 and reflected by a mirror 32 disposed at an inclination of 45 degrees with respect to the optical path, whereby the traveling direction is bent by 90 degrees.

  On the optical path of the reflected light by the mirror 32, a half mirror 34, a reference plane plate 36, a lens 80 to be tested, and a reflection reference concave mirror 38 are arranged in this order from the mirror 32 side. The light reflected by the mirror 32 is transmitted through a half mirror 34 disposed at an inclination of 45 degrees with respect to the optical path, and is incident on a reference plane plate 36.

  The reference flat plate 36 is a flat glass plate whose surface is polished with high accuracy, and a reference surface 36 a is provided on a surface far from the half mirror 34. The reference surface 36a has a property of transmitting part of the light incident on the reference flat plate 36 and reflecting the rest. By utilizing this property, it is possible to obtain interference fringes between the light reflected by the reference surface 36a and the light that has passed through the reference surface 36a and then passed through the lens 80 to be tested. The test lens 80 is held by the holding unit 11. A known lens holding device can be used as the holding unit 11.

  The reference wavefront light reflected by the reference surface 36 a is reflected by the half mirror 34, passes through the condenser lens 35, and then enters the CCD 41 through the pinhole 37 disposed on the optical path. Instead of the CCD 41, other imaging devices (for example, CMOS (Complementary Metal Oxide Semiconductor)) can be used.

On the other hand, the wavefront to be detected that has been transmitted through the reference surface 36 a and transmitted through the test lens 80 and then reflected by the reflection standard concave mirror 38 is transmitted through the reference plane plate 36 again. The wavefront to be detected is reflected by the half mirror 34 and then enters the CCD 41 through the condenser lens 35 and the pinhole 37. Interference fringes are formed by the interference between the wavefront to be detected and the reference wavefront light from the reference surface 36a. The formed interference fringes are converted into electrical signals by the CCD 41 and input to the interference fringe analysis unit 42.
In the present embodiment, interference fringes are formed by the reference wavefront by the reference surface 36a and the test wavefront that is transmitted through the reference surface 36a and the test lens 80 and reflected by the reflection standard concave mirror 38. It is also possible to replace the test wavefront with an optical element having a reflection surface instead of the test lens 80 and replace it with the test wavefront caused by this surface reflection to form interference fringes.

  The reference flat plate 36 is held by a support device (for example, an electric θ stage) 51. The support device 51 is connected to the control unit 43 via a reference plane plate driving unit 52. The reference flat plate drive unit 52 that has received the drive signal output from the control unit 43 supplies a predetermined drive current to the support device 51, whereby the support device 51 uses the optical axis of the reference flat plate 36 as a reference. It can be inclined by an arbitrary angle (predetermined angle) θ with respect to the traveling direction of the incident light on the flat plate 36. By inclining the reference flat plate 36 (reference surface 36a) in this way, interference fringes (space carriers, tilt fringes) corresponding to the inclination angle are generated. By analyzing the interference fringes obtained in this way, the wavefront aberration of the lens 80 can be analyzed.

  As shown in FIG. 2, the interference fringe analysis unit 42 includes an A / D converter 421, a frame memory 422, a D / A converter 423, a calculation unit 424, and an overlay memory 425. As the interference fringe analysis unit 42, for example, a personal computer can be used. However, the A / D converter 421, the frame memory 422, the D / A converter 423, the calculation unit 424, and the overlay memory 425 are independent devices. You may comprise as.

  Signal charges (interference fringe image signals) accumulated in each pixel are sequentially input from the CCD 41 to the A / D converter 421. In the A / D converter 421, each input analog signal is converted into a digital signal (interference fringe image data). The interference fringe image data is stored at an address corresponding to the pixel of the CCD 41 in the frame memory 422 connected to the A / D converter 421.

  The interference fringe image data stored in the frame memory 422 can be converted into an analog signal by the D / A converter 423 connected to the frame memory 422. The converted analog signal is displayed on an output unit 44 (for example, a monitor, a CRT display, a liquid crystal display, or a printer) provided outside the interference fringe analysis unit 42. Conventional interference fringe analysis can be performed by the display on the output unit 44.

  The overlay memory (reference image storage unit) 425 stores reference pattern image data (reference pattern image data) in which black and white stripes are alternately arranged as shown in FIG. The black and white frequency of the data of the reference pattern image is matched with the analysis frequency.

  The calculation unit 424 connected to the frame memory 422 and the overlay memory 425 sequentially reads the interference fringe image data stored in the frame memory 422 and the reference pattern image data stored in the overlay memory 425, and sequentially superimposes them. Thus, a moire image is formed. The moire image data thus obtained (moire image data) is output to the output unit 44 via the D / A converter 423.

  Further, the computing unit 424 can analyze the wavefront aberration of the lens 80 to be analyzed by analyzing the interference fringe image data output from the frame memory 422 using the spatial phase shift method described below.

  An input unit 45 (for example, a keyboard and a mouse) and a reference plane plate driving unit 52 are connected to the control unit 43. Based on the signal input from the input unit 45, the control unit 43 outputs a control signal necessary for setting the attitude of the reference flat plate 36 to the reference flat plate driving unit 52. Based on this control signal, the reference flat plate driving unit 52 supplies a driving current necessary for setting the posture of the reference flat plate 36 to the support device 51.

ここで、ａは平均強度分布、ｂは振幅、νは空間キャリアの空間周波数（解析用周波数）であり、φはある点における初期位相である。Ｉ_jはＣＣＤ４１に入射される干渉縞強度であり、Ａ／Ｄ変換部４２１を介してフレームメモリ４２２に記憶された干渉縞画像データから得られる。この式Ａを被検レンズ８０の各点における空間（ｘ，ｙ）に繰り返し適用する。添字ｊは１周期内の空間座標を示し、ｊ＝０〜Ｎ−１（Ｎ＞３）の値をとる。ここで、Ｎは干渉縞１周期分の周期を示し、Ｎ＝１／νで表される。つまり、干渉縞１周期がＣＣＤのＮ画素に合致すると干渉縞解析が可能となる。 Here, an interference fringe analysis method and an aberration measurement method using the spatial phase shift method will be described.
When the optical axis of the reference plane plate 36 is inclined with respect to the traveling direction of the incident light on the reference plane plate 36, a tilt interference fringe on which spatial carriers are superimposed is obtained. A spatial signal intensity distribution I _j within one period represented by the following expression A is established for one period with the tilt interference fringes.

<Formula A>

Here, a is the average intensity distribution, b is the amplitude, ν is the spatial frequency (analysis frequency) of the spatial carrier, and φ is the initial phase at a certain point. I _j is the interference fringe intensity incident on the CCD 41 and is obtained from the interference fringe image data stored in the frame memory 422 via the A / D converter 421. This formula A is repeatedly applied to the space (x, y) at each point of the lens 80 to be examined. The subscript j indicates a spatial coordinate within one period, and takes a value of j = 0 to N−1 (N> 3). Here, N indicates a period corresponding to one period of interference fringes, and is represented by N = 1 / ν. That is, interference fringe analysis is possible when one period of interference fringes matches the N pixels of the CCD.

この式により被検レンズ８０の各点における初期位相を求めることができ、２次元的にこれを繰り返せば、被検レンズ８０の波面収差の空間分布を定量的に求めることができる。
ここで基準平面板の配置角度をθとする。初期の基準光の波長がλ₀であり、干渉縞を撮影するＣＣＤ４１の大きさがｄ、画素数がＭであるとする。この時発生するｔｉｌｔ縞によるＣＣＤ４１の両端における位相差ｈは以下の式で表すことができる。

ここで、ｍはｔｉｌｔ縞の本数（白黒一対）を表す。また、ＣＣＤ４１で撮影された干渉縞画像データにおいて、ＣＣＤ４１の全画素数Ｍは ｔｉｌｔ縞の本数ｍとｔｉｌｔ縞の周期に合致した画素数（＝１／ν）を掛けたものである。

上記の式を展開し、ｔｉｌｔ縞の本数ｍを消去すると、

ここで、基準平面板の配置角度θとＣＣＤ４１の画素数Ｍは機械的に決められており、これが不変である。故に干渉計の光源波長がλ₁に変更されても、以下の関係が成り立つ。
＜式Ｃ＞

（ｋ：定数）
すなわち、式Ｃにおける定数ｋを算出しておけば、基準光の波長が変更されても、基準光の波長λ₁から、解析用周波数ν₁を算出でき、これを用いた干渉縞解析が可能となる。つまり、参照面３６ａの傾斜角度を調整することなく、解析用周波数を算出することにより、被検レンズ８０の干渉縞解析及び収差測定を行うことができる。 Regarding the formula (A), it is assumed that a and b take a constant value, and the initial phase φ is expressed by the following formula B from the signal intensity of N pixels.
<Formula B>

By this equation, the initial phase at each point of the test lens 80 can be obtained. By repeating this two-dimensionally, the spatial distribution of the wavefront aberration of the test lens 80 can be obtained quantitatively.
Here, the arrangement angle of the reference plane plate is θ. Assume that the wavelength of the initial reference light is λ ₀ , the size of the CCD 41 that captures interference fringes is d, and the number of pixels is M. The phase difference h at both ends of the CCD 41 due to tilt stripes generated at this time can be expressed by the following equation.

Here, m represents the number of tilt stripes (monochrome pair). In the interference fringe image data captured by the CCD 41, the total number of pixels M of the CCD 41 is obtained by multiplying the number m of the tilt stripes by the number of pixels (= 1 / ν) that matches the period of the tilt stripes.

Expanding the above equation and erasing the number m of tilt stripes,

Here, the arrangement angle θ of the reference plane plate and the number of pixels M of the CCD 41 are mechanically determined and are unchanged. Therefore, even if the light source wavelength of the interferometer is changed to λ ₁ , the following relationship holds.
<Formula C>

(K: constant)
In other words, if the constant k in Equation C is calculated, the analysis frequency ν ₁ can be calculated from the reference light wavelength λ ₁ even if the reference light wavelength is changed, and interference fringe analysis using this can be performed. It becomes. That is, the interference fringe analysis and aberration measurement of the lens 80 can be performed by calculating the analysis frequency without adjusting the tilt angle of the reference surface 36a.

  In the spatial phase shift method, the image needs to be captured only once, and if the inclination angle of the reference plane plate 36 is determined, there is no need to change the interval between the reference plane plate 36 and the lens 80 to be examined. Therefore, the interference fringe analysis can be performed at low cost and in a short time, and the wavefront aberration of the lens 80 can be obtained each time the interference fringe analysis is performed.

  If the wavefront aberration obtained as described above is expanded by Zernike in the calculation unit 424, a more detailed analysis can be performed. In other words, each coefficient of the polynomial after Zernike expansion indicates the aberration information of the lens 80 to be measured in detail for each type of aberration, and the larger the number, the more information that can be obtained. Therefore, when these coefficients are analyzed, the aberration of the test lens 80 can be analyzed in more detail and quantitatively.

Next, the flow of interference fringe analysis and aberration measurement of the test lens 80 will be described with reference to FIG.
First, out of light perpendicularly incident on the reference plane plate 36, the wavefront to be detected that has passed through the reference plane plate 36, reflected by the reflective reference concave mirror 38, and again transmitted through the reference plane plate 36, and reflected by the reference plane plate 36. The components of the semiconductor laser 21, the CCD 41, and the optical system 30 are arranged so that the reference wavefront follows the same optical path and enters the CCD 41, and operations of interference fringe analysis and optical adjustment are started (steps). S100). Since it is confirmed by a well-known method whether or not it has entered along the same optical path, the description thereof is omitted here.

  Subsequently, the operator operates the input unit 45, and a control signal corresponding to the tilt angle (an angle corresponding to the frequency of the initial reference light) input from the control unit 43 to the reference flat plate driving unit 52. Is output. Upon receiving this control signal, the reference plane plate driving unit 52 supplies a drive current necessary for the reference plane plate 36 to tilt with respect to the optical axis to the support device 51. As a result, the reference flat plate 36 is inclined with respect to the optical axis in accordance with the frequency of the initial reference light. (Step S101) (initial reference light alignment).

The alignment for initial reference light in step S101 will be described with reference to FIG. 4B (steps S200 to S207).
First, in order to perform alignment corresponding to the initial reference light λ ₀ , an initial frequency setting value ν ₀ is set. (Step S201). Subsequently, by operating the driver 22, the initial reference light is emitted from the semiconductor laser 21 (step S202). The emitted light is reflected by the mirror 32 through the collimator lens 31, passes through the half mirror 34, and enters the reference flat plate 36. A part of the incident light is reflected by the reference surface 36 a of the reference plane plate 36, reflected by the half mirror 34, and then enters the CCD 41 through the condenser lens 35 and the pinhole 37. The light that has not been reflected by the reference surface 36a passes through the test lens 80 and then enters the reflection reference concave mirror 38. If the test lens 80 is correctly arranged, the light is reflected so as to follow the same optical path as the incident light. Reflected light from the reflective reference concave mirror 38 passes through the test lens 80 and the reference flat plate 36 again, is reflected by the half mirror 34, and then enters the CCD 41 through the condenser lens 35 and the pinhole 37. The CCD 41 has interference fringes (steps) formed by a reference wavefront by the reference surface 36a and a test wavefront that has been transmitted through the reference plane plate 36 and then transmitted through the test lens 80 and reflected by the reflective reference concave mirror 38. S203) is incident (step S204). The interference fringes are stored at addresses corresponding to the pixels of the CCD 41 in the frame memory 422.

  The calculation unit 424 sequentially reads the interference fringe image data stored in the frame memory 422 and the reference pattern image data stored in the overlay memory 425, and forms the moire image by sequentially superimposing these (Step S205). This is output to the control unit 43.

  In the output unit 44, it is determined whether the moire image is in a so-called one-color state (hereinafter referred to as one-color) where the brightness is almost uniform over the entire surface (step S206). If it is one color (YES in step S206), the setting of the initial reference light alignment is completed (step S207), and the interference fringe analysis (FIG. 4A) is returned.

If the color is not one color (NO in step S206), the control unit 43 outputs an inclination adjustment signal to the reference flat plate driving unit 52 (step S208). The interference fringes (step S203) formed again by emitting the reference light (step S202) enter the CCD 41 (step S204), and the interference fringe image data is stored in the frame memory 422 via the A / D converter 421. The In the calculation unit 424, a moire image is newly formed by the interference fringe image data and the reference pattern image data (step S205), and is output to the control unit 43, where it is analyzed again whether it is one color (step S205). S206). If it is one color (YES in step S206), the alignment for the initial reference light is finished (step S207). If it is not one color (NO in step S206), the inclination adjustment of the reference plane plate is again performed (step S208). Is made. The above flow is repeated until the moire image becomes one color.

After performing the alignment for initial reference light, the wavelength actually measured is set (step S102). This is the wavelength of the initial reference light or the reference light whose wavelength has been changed, which will be described later.
Next, a fringe analysis frequency corresponding to the wavelength set in step S102 is set. When the wavelength to be set is the initial reference light, the numerical value set in step S201 is used by using the wavelength λ ₀ of the initial reference light and the initial analysis frequency ν ₀ to use the changed wavelength λ _1. , applied to the expression C, calculates the analysis frequency [nu ₁ at the wavelength lambda _1, which is set (step S103).

After setting the analysis frequency, the reference light is emitted from the semiconductor laser 21 by operating the driver 22 (step S104). In the same manner as described above, the emitted light is reflected by the mirror 32 through the collimator lens 31, passes through the half mirror 34 and enters the reference plane plate 36, and the reference wavefront by the reference plane 36a and the reference plane plate 36. Then, an interference fringe (step S105) formed by the wavefront to be detected which has been transmitted through the lens 80 and reflected by the reflection reference concave mirror 38 enters the CCD 41 (step S106).

The formed interference fringes can be analyzed by display on the output unit 44, and detailed and quantitative analysis can also be performed by calculating the phase in the interference fringe analysis unit 42 (step S107). The formation of the interference fringes, the display on the output unit 44, and the calculation of the phase in the interference fringe analysis unit 42 are performed continuously unless the operator stops the operation of the interference fringe forming unit 20, and the phase distribution (wavefront aberration) ) Is stored in the storage unit 46.

When the operator does not wish to continue the interference fringe analysis (YES in step S108), the interference fringe analyzer stops its operation by the operator operating the input unit 45 (step S109). On the other hand, when the interference fringe analysis is continued (NO in step S108), the operation of the interference fringe analysis apparatus is continued by the operator operating the input unit 45. Here, when changing the wavelength of the reference light (YES in step S110), the control unit 43 instructs the driver 22 so that the semiconductor laser 21 emits the wavelength of the value input from the input unit 45 by the operator. A control signal is output (step S102). When the wavelength of the reference light is not changed (NO in step S110), the semiconductor laser 21 continuously emits the reference light having a wavelength that has already been set (step S104).

As described above, when the interference fringe analysis is performed by the spatial phase shift method while changing the wavelength of the reference light in the multiwavelength interferometer, according to the wavelength of the reference light (the wavelength of the incident light on the reference plane plate), The analysis frequency is set as a parameter, and interference fringes are analyzed using the set frequency, so that the spatial carrier modulated by changing the wavelength of the reference light can be handled at high speed and at low cost. be able to.

Although the present invention has been described with reference to the above embodiment, the present invention is not limited to the above embodiment, and can be improved or changed within the scope of the purpose of the improvement or the idea of the present invention.

It is a figure which shows the structure of the interference fringe analysis apparatus used for the interference fringe analysis method and aberration measuring method which concern on embodiment of this invention. It is a figure which shows the structure of the interference fringe analysis part which concerns on embodiment of this invention. It is a figure which shows the example of the reference | standard pattern image data which concerns on embodiment of this invention. (A) is a flowchart which shows the flow of the interference fringe analysis method which concerns on embodiment of this invention, (b) is a flowchart which shows the flow of the subroutine which performs alignment corresponding to initial stage reference light.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Holding part 20 Interference fringe formation part 21 Semiconductor laser 30 Optical system 36 Reference plane board 36a Reference surface 38 Reflection reference concave mirror 41 CCD
42 Interference fringe analysis unit 43 Control unit 44 Output unit 45 Input unit 46 Storage unit 80 Test lens (optical element)
422 frame memory 424 arithmetic unit 425 overlay memory

Claims (2)

In order to perform interference fringe analysis using a spatial carrier, a tilt interference fringe frequency setting step for setting a frequency of a tilt interference fringe as an interference fringe analysis parameter;
In the interferometer, a tilt interference fringe forming step for causing a reference wavefront from the tilted reference surface and a test wavefront from the test surface to interfere to form a tilt interference fringe in which spatial carriers are superimposed;
A tilt interference fringe alignment step in which the reference plane is tilted so that the frequency set in the tilt interference fringe frequency setting step and the frequency of the tilt interference fringe formed in the tilt interference fringe formation step are equal to each other;
When the light source wavelength of the interferometer is changed , instead of the frequency of the tilt interference fringe set in the tilt interference fringe frequency setting step, the tilt interference fringe calculates the frequency of the tilt interference fringe according to the changed light source wavelength. A frequency calculation step;
Tilt interference pattern formed by the tilt fringes forming step, when changing the light source wavelength of the interferometer is the interference fringe analysis using the frequency of the tilt fringes calculated in the tilt fringe frequency calculation step In the case where the light source wavelength of the interferometer is not changed, an interference fringe analysis step in which interference fringe analysis is performed using the frequency of the tilt interference fringe set in the tilt interference fringe frequency setting step ;
An interference fringe analysis method comprising: In order to perform an interference fringe analysis using a spatial carrier, a tilt interference fringe frequency setting step for setting a tilt interference fringe frequency as an interference fringe analysis parameter;
In the interferometer, a tilt interference fringe forming step for causing a reference wavefront from the tilted reference surface and a test wavefront from the test surface to interfere to form a tilt interference fringe in which spatial carriers are superimposed;
A tilt interference fringe alignment step in which the reference plane is tilted so that the frequency set in the tilt interference fringe frequency setting step and the frequency of the tilt interference fringe formed in the tilt interference fringe formation step are equal to each other;
When the light source wavelength of the interferometer is changed , instead of the frequency of the tilt interference fringe set in the tilt interference fringe frequency setting step, the tilt interference fringe calculates the frequency of the tilt interference fringe according to the changed light source wavelength. A frequency calculation step;
tilt fringe, when you change the light source wavelength of the interferometer, using said frequency of tilt fringes calculated in tilt fringe frequency calculating step is interference fringe analysis, does not change the light source wavelength of the interferometer In the case, an interference fringe analysis is performed using the frequency of the tilt interference fringe set in the tilt interference fringe frequency setting step, and the aberration is measured based on one of the analysis results;
An aberration measuring method comprising:

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