High-accuracy single F-P plate angular displacement measurement instrument

[0019] Please refer to FIG. 1, which is a schematic diagram of the structure of the high-precision single F-P plate angular displacement measuring instrument of the present invention. The high-precision single FP plate angular displacement measuring instrument of the present invention includes: a modulated light source 2 with a driving power source 1, a beam collimating objective lens 3 and a reflecting mirror 4 are arranged along the forward direction of the light beam emitted by the modulated light source 2 The object 5 to be measured is placed in the forward direction of the reflected light beam of the mirror 4. An F-P plate 6 and a beam splitter 7 are arranged in the forward direction of the reflected light of the object 5 to be measured. A lens 8 and a photoelectric conversion element 9 are arranged in the direction of the transmitted light beam at the port b of the beam splitter 7. The photoelectric conversion element 9 is connected to the analog-to-digital conversion element 10 connected to the computer 13. A photoelectric conversion element 11 is arranged in the direction of the reflected light beam at the port c of the beam splitter 7, and the photoelectric conversion element 11 is connected to the analog-to-digital conversion element 12 connected to the computer 13.

[0020] The modulated light source 2 mentioned above is a semiconductor laser (also called a laser diode, or LD for short).

[0021] The driving power supply 1 provides DC and sinusoidal AC signals to the modulated light source 2.

[0022] The photoelectric conversion element 9 is a photodiode, a photovoltaic cell, or the like.

[0023] The photoelectric conversion element 11 is a CCD image detector.

[0024] The beam splitter 7 refers to an element capable of splitting the incident light into two beams at a light intensity ratio close to 1:1. Such as light splitting prisms, parallel plates coated with light-separating film and anti-reflection film on both sides, etc.

[0025] The F-P plate 6 is a transparent flat plate with two parallel sides.

[0026] The measured object 5 refers to an optical surface that produces angular displacement, such as a mirror surface, a silicon wafer surface, a metal surface, and so on.

[0027] The specific working process of the high-precision single FP plate angular displacement measuring instrument of the present invention is: the light emitted by the modulated light source 2 with the driving power supply 1 passes through the collimating objective lens 3 and is reflected by the reflector 4 to the measured object 5, and the measured object 5 reflects The beam of light irradiates the beam splitter 7 through the FP plate 6. The beam splitter 7 divides the incident light into reflected light and transmitted light. The reflected light is emitted from the port c of the beam splitter 7 to the photoelectric conversion element 11. The electrical signal output by the photoelectric conversion element 11 is converted into a digital signal by the analog-to-digital conversion element 12 and then enters the computer 13; the port b of the beam splitter 7 exits The transmitted light is condensed by the lens 8 to the photoelectric conversion element 9, and the electrical signal output by the photoelectric conversion element 9 is converted into a digital signal by the analog-to-digital conversion element 10 and enters the computer 13.

[0028] When the photoelectric conversion element 9 detects the interference signal

[0029] s(t)=cos(zcos(ωt+θ)+α), (1)

[0030] Where s(t) is the interference signal generated by the two beams formed by the beam passing through the F-P plate 6. z is the phase modulation amplitude of the interference signal s(t), ω is the frequency of the sinusoidal phase modulation signal of the driving power supply 1, t is time, and α is the phase change of the interference signal s(t) caused by the rotation of the object 5 to be measured. Take the initial phase of α as zero

[0031] α = 4 πnh λ [ cos i 1 - cos ( i 1 + 2 iΔ ′ ) ] . - - - - - - ( 2 )

[0032] Where λ is the center wavelength of light source 2. n and h are the refractive index and the distance between the upper and lower surfaces of the F-P plate 6 respectively. i 1 Is the refraction angle in the F-P plate corresponding to the initial incident angle i, i 1 +Δi' is the angle of refraction in the F-P plate corresponding to the incident angle i+Δi. see figure 2. From the formula (2)

[0033] Δi ′ = α ( 4 πnh / λ ) sin i 1 . - - - - - - - - ( 3 )

[0034] The angular displacement δ of the measured object 5 can be obtained by the following formula

[0035] δ = Δ i ′ 2 1 - sin 2 i 1 1 - n 2 sin 2 i 1 = α ( 8 πh / λ ) sin i 1 1 - sin 2 i 1 1 - n 2 sin 2 i 1 . - - - - - - - ( 4 )

[0036] (4) Sini in the formula 1 There is the following relationship with the horizontal distance d between the two beams of light transmitted from the F-P plate 6:

[0037] sin i 1 = { [ ( 1 + d 2 4 h 2 ) + ( 1 + d 2 4 h 2 ) 2 - 4 n 2 d 2 4 h 2 ] / ( 2 2 ) } 1 / 2 . - - - - - - - ( 5 )

[0038] The light emitted by the modulated light source 2 with the driving power supply 1 passes through the collimating objective lens 3 and is reflected by the reflector 4 to the measured object 5, and the light beam reflected by the measured object 5 is divided into two beams by the F-P plate 6 to cause interference. The interference light irradiated on the beam splitter 7 is divided into two paths of transmitted light and reflected light. The transmitted light is condensed by the lens 8 to the photoelectric conversion element 9. The analog-to-digital conversion element 10 converts the interference signal s(t) detected by the photoelectric conversion element 9 into a digital signal and inputs it into a computer for processing. Analysis can get α. The reflected light from the beam splitter 7 irradiates the photoelectric conversion element 11, and the analog-digital conversion element 12 converts the light intensity distribution signal detected by the photoelectric conversion element 11 into a digital signal, which is input to the computer for information processing to obtain the d value. n and h are the parameters of the F-P board 6, which are substituted into equation (5) together with d to obtain sini. Substituting α and sini and instrument parameters λ, n and h into equation (4) can obtain the angular displacement of the measured object 5.

[0039] If the wavelength of the modulated light source 2 is selected to be 661 nm, the refractive index and thickness of the F-P plate 6 are 1.5163 and 12 mm, respectively. Since the sinusoidal phase modulation method is used to measure the phase change α of the interference signal, the measurement resolution is above 0.01rad. Substituting the above data into equation (4), it can be obtained that the measurement resolution of angular displacement δ is 10 -8 rad order of magnitude.

[0040] The high-precision single F-P plate angular displacement measuring instrument of the present invention can be used to measure the angular displacement of a rotating object.

[0041]Figure 1 is the structure of the high-precision single F-P plate angular displacement measuring instrument of the present invention. Among them, the modulated light source 2 uses a single-mode semiconductor laser with a center wavelength of 661 nm. Driven by the DC and AC signals provided by the driving power supply 1, the emitted light passes through the collimating objective lens 3 and is reflected by the reflector 4 to the measured object 5, and the light beam reflected by the measured object 5 is divided into two beams by the FP plate 6 to cause interference . The F-P plate 6 is a glass plate with two sides highly parallel, and its surface is coated with a 90% anti-reflection film at a wavelength of 661 nm, and its refractive index and thickness are 1.5163 and 12 mm, respectively. The interference light irradiated on the beam splitter 7 is divided into two paths of transmitted light and reflected light. The beam splitter 7 adopts a parallel flat plate with a light-reducing film and an anti-reflection film on both sides. The transmitted light is condensed by the lens 8 to the photoelectric conversion element 9, and the photoelectric conversion element 9 is a photodiode. The analog-to-digital conversion element 10 converts the interference signal s(t) detected by the photoelectric conversion element 9 into a digital signal to be input to a computer for processing, and α can be obtained by performing spectrum analysis on s(t). The reflected light from the beam splitter 7 irradiates the photoelectric conversion element 11, which is a CCD image detector. The analog-to-digital conversion element 12 converts the light intensity distribution signal detected by the photoelectric conversion element 11 into a digital signal and inputs it to the computer 13 for processing. We can obtain d. n and h are the parameters of the F-P board 6, which are substituted into equation (5) together with d to obtain sini. Substituting α and sini and parameters λ, n and h into equation (4) can obtain the angular displacement of the measured object 5. Its measurement resolution is 10 -8 rad order of magnitude.

[0042] The trial shows that the present invention has the following advantages:

[0043] 1. The invention uses CCD to detect the center distance of the two transmitted beam spots of the F-P plate, and obtains the initial angle of the incident light through simple calculations. It solves one of the difficult problems of using F-P plate interferometry to measure angular displacement, that is, the problem of determining the initial angle of incident light.

[0044] 2. The single F-P plate sinusoidal phase modulation laser interferometer of the present invention has a simple structure and can perform high-precision angular displacement measurement.

[0045] 3. Compared with the prior art [1], the present invention uses sinusoidal phase modulation interferometry to measure the angular displacement of the object by measuring the phase of the interference signal, which enhances the anti-interference ability of the instrument against stray light and reduces the measurement error of the instrument , Improve the measurement accuracy of the instrument.