CN109974629B - Method for measuring groove angle of transmission type plane blazed grating - Google Patents
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Abstract
The application discloses a method for measuring a groove angle of a transmission type plane blazed grating, which comprises the following steps: making parallel light beams emitted by the linear light source enter the blazed grating along the normal direction of the grating surface, and recording an initial angle K1 between a reference line and a zero position of the blazed grating at the moment, andthe light energy value of the linear light source; keeping a light source still, rotating the blazed grating along the central axis of the blazed grating, and continuously detecting the diffracted light energy value emitted from the scored small plane of the blazed grating, wherein when the absolute value of the difference value between two T values of the blazed grating rotating every 1 degree is greater than or equal to 5%, a termination angle K2 is recorded; the blazed grating groove angle θ is calculated according to the following formula:
wherein n is the refractive index of the blazed grating substrate material, and K is K2-K1. The measuring method of the groove angle is simple in measuring light path, low in experimental requirement, free of slicing and free of damage to the blazed grating to be measured.
Description
Technical Field
The application relates to the field of optics, in particular to a method for measuring a groove angle of a transmission type plane blazed grating.
Background
When the grating is scribed into sawtooth-shaped groove sections, the light energy of the grating is concentrated in a predetermined direction, i.e. a certain spectral order. When detecting from this direction, the intensity of the spectrum is at its maximum, a phenomenon known as blaze (blaze), and such gratings are known as blazed gratings. According to the working principle, the grating can be divided into a transmission type blazed grating and a reflection type blazed grating.
One side of the transmission type plane blazed grating is a grating surface, one side of the transmission type plane blazed grating is a sawtooth shape, one side of the sawtooth shape is provided with a plurality of indented small planes, and an included angle theta is formed between each indented small plane and the grating surface and is called a groove-shaped angle. The processing error of the groove angle can directly cause errors of diffraction efficiency, resolution, stray light and the like of the grating, and further influences the quality of a test spectrum, and at present, the commonly used method for measuring the groove angle mainly comprises the following two methods:
(1) and (4) directly measuring. Firstly, the transmission type plane blazed grating is taken as a mother plate to be copied, then the copied grating substrate is separated from the mother plate and solidified, finally, the copied grating substrate is cut into slices, and the groove angle of the copied substrate is directly observed and measured by an electron microscope. The accuracy of the measurement of this method is limited by the quality of the replication and the slicing, and may cause irreparable damage to the grating during replication.
(2) The reverse method. Obtaining a spectrogram of the transmission type plane blazed grating by utilizing a Fourier mode theory, simulating a measurement spectrogram in an experiment by adding Gaussian noise, selecting a proper inversion algorithm according to an evaluation function, determining the range of parameters, and searching the value of the parameter to be measured. The method has complex principle, more deduction steps and error as high as 5 percent.
Disclosure of Invention
In view of the above-mentioned shortcomings of the existing measurement method for the groove angle of the blazed grating, the application provides a measurement method for the groove angle of the transmission type plane blazed grating, the groove angle can be measured without copying and slicing the blazed grating, the operation steps are simple, and the transmission type plane blazed grating is not damaged.
The technical problem that this application will further solve is to look for suitable measurement parameters, makes the deduction step of flute angle simpler.
In order to achieve the above purpose, the embodiment of the present application adopts the following technical solutions:
a method for measuring the groove angle of a transmission type plane blazed grating comprises the following steps:
enabling parallel light beams emitted by a linear light source to enter the blazed grating along the normal direction of the grating surface, and recording an initial angle K1 between a reference line and a zero position of the blazed grating at the moment and the light energy value of the linear light source; keeping a light source still, rotating the blazed grating along a central axis of the blazed grating, and continuously detecting the diffracted light energy value emitted from the scored small plane of the blazed grating, and recording an end angle K2 when the absolute value of the difference between two T values of the blazed grating which rotate by 1 degree is larger than or equal to 5%, wherein the central axis is a normal line which is perpendicular to a grating surface and a normal line of any scored small plane at the same time and passes through the axis of the blazed grating; the value of T is: the diffracted light energy value/light energy value of the line light source for a current angle;
calculating the blazed grating groove angle theta according to the following formula:
wherein n is the refractive index of the blazed grating substrate material, and K is K2-K1.
The central axis of the blazed grating is the normal perpendicular to the grating surface and the normal of any scored facet, and the axis passing through the blazed grating can be selected in various ways. The line light source refers to a light source capable of providing a single wavelength. The datum line is a reference line selected from a blazed grating, and the included angle value between the projection line of the datum line on the accurate rotating table and the zero position is the reading value of K1 or K2.
Parallel light rays of monochromatic light are selected to enter the blazed grating from the grating surface, are refracted by the blazed grating and then are incident on the scored small plane, the angle of the parallel light rays entering the grating, namely the angle of the first incident angle, can generate different optical phenomena on the scored small plane, and the diffracted light energy in the transmission direction is different. When the first incident angle is adjusted, the incident angle on the scored facet after the blazed grating is refracted, namely the second incident angle is just equal to the critical angle of total reflection formed by the blazed grating substrate material and air, the energy of the diffracted light emitted by the blazed grating on the scored facet can be suddenly changed, and the sudden change is easily sensed by the light detector. By utilizing the phenomenon, two optical paths are selected to collect angle data, and then the groove angle of the blazed grating is calculated:
the first light path: parallel light beams emitted by a linear light source are incident to the blazed grating along the normal direction of the grating surface, after entering the grating, the light rays do not change the propagation direction and continue to propagate to the scored small plane along the normal direction of the grating surface, in the light path, the first incidence angle is equal to 0 degree, and an initial angle K1 between the reference line and the zero position of the blazed grating and the light energy value of the linear light source at the moment are recorded; a second light path: parallel light beams emitted by the linear light source are incident on the grating surface at a first incident angle k, the parallel light beams are refracted in the blazed grating at the moment, the refraction angle is i, the refracted light rays continue to spread forwards to reach the scored small plane, and the incident angle on the scored small plane, namely the second incident angle alpha is just equal to the critical angle of total reflection formed by the substrate material of the blazed grating and air at the moment. In this optical path, since the light beam incident from the linear light source is finally totally reflected on the scored facet, the energy of the diffracted light emitted from the scored facet of the blazed grating is abruptly changed, and this abrupt change is easily sensed by the light detector, and in the actual measurement, we can choose to record the end angle K2 between the reference line and the zero position of the blazed grating when the absolute value of the difference between two T values of the blazed grating rotating every 1 ° is ≧ 5%, where the T values are: the diffracted light energy value for the current angle/the light energy value for the line light source.
The first optical path is set to be in an initial state of testing, the second optical path is set to be in a termination state of testing, the first optical path is switched to the second optical path, and the blazed grating can be rotated around the central shaft. Since the incident line of the initial state light is parallel to the normal of the grating surface, by precisely controlling the rotation of the blazed grating, when the blazed grating rotates to the termination state, the blazed grating rotates by an angle equal to the first incident angle K of the termination state, that is, K is K2-K1, and the refraction angle i at this time can be calculated by snell's law of refraction:
wherein k is a first incident angle of light entering the blazed grating through the grating surface, i is a refraction angle, n is a refractive index of the blazed grating substrate material, and the refractive index of air is 1.
The light further propagates forward, incides on the nick facet, takes place the total reflection this moment, and the second incident angle alpha of light incidence on the nick facet satisfies following equivalence relation according to right triangle's principle:
α＝i+θ..................(2)
where i is the angle of refraction and θ is the angle of the trough, i.e., the angle between the facet of the mark and the grating surface.
Meanwhile, according to the law of total reflection, the critical angle of total reflection formed by the blazed grating substrate material and the air, the second incident angle α also satisfies the following equivalent relation:
where n is the refractive index of the blazed grating substrate material.
The value of the groove angle θ can be obtained by substituting the formula (1) and the formula (3) into the formula (2), and specifically, the following values are obtained:
by the method, only two angles K1 and K2 need to be measured, and the groove angle can be accurately calculated. In addition, the light path is simple, the test requirement is low, the rotating angle value of the blazed grating when the blazed grating is converted from the first light path to the second light path in the measuring process is measured by monitoring the diffracted light energy emitted by the blazed grating on the indented facet, the rotating angle value of the groove angle is deduced by the rotating angle value, the principle is simple, and the deduction steps are few.
Preferably, the reference line is one of the following lines: the normal line of the grating surface of the blazed grating, the normal line of the indented facet, the extension line of the grating surface or the extension line of the indented facet. The reference line can be selected for convenience of reading.
Preferably, the linear light source is a metal vapor lamp, an air cathode lamp or a light source emitted by a laser emitter.
Preferably, the metal vapor lamp is a mercury lamp or a sodium vapor lamp.
Preferably, the laser emitter emits light having a wavelength of 632.8 nm.
Preferably, the diffracted light energy is detected using one of the following optical detectors: a selenium photocell, a photodiode, a photomultiplier, a silicon diode array detector, an optical power meter, or a semiconductor detector.
Compared with the prior art, the method has the following advantages:
(1) the groove angle measuring method can measure the groove angle without copying and slicing the blazed grating, has simple operation steps and cannot damage the transmission type plane blazed grating;
(2) the measuring method of the groove angle has the advantages of simple measuring light path and low experimental requirement;
(3) the method for measuring the groove angle is simple in principle, few in deduction steps, high in detection accuracy and only 2.8% in measurement error.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.
FIG. 1 is a schematic diagram of a test optical path of a method for measuring a groove angle of a transmission type blazed grating according to the present application;
FIG. 2 is an optical path diagram of an initial state of a test of a method for measuring a groove angle of a transmission type blazed grating according to the present application;
fig. 3 is an optical path diagram of an end state of a test of a method for measuring a groove angle of a transmissive blazed grating according to the present application.
Detailed Description
The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
As shown in fig. 1, 2 and 3, a measuring method of a groove angle of a transmission type plane blazed grating is characterized in that before a test is started, a test light path is set up, specifically as shown in fig. 1, a blazed grating 1 to be measured is vertically arranged on a precision rotary table 2, and a central shaft of the blazed grating 1 is overlapped with a rotation axis of the precision rotary table 2, namely, a rotation axis of the precision rotary table 2 is perpendicular to a normal line of a grating surface and a normal line of any scored facet at the same time and penetrates through the blazed grating. The rotary table is provided with zero lines and lines for marking angles, the standard line of the blazed grating 1 is mainly used for reading, and various setting modes can be provided, the normal of the grating surface 11 is selected as the standard line of the blazed grating 1 and is used for reading an initial angle K1 value and a final angle K2 value, wherein the maximum angular speed of the precision rotary table is not more than 40 degrees/s, and the precision is controlled to be +/-0.01 degrees. For example, a precision rotary table 2 of URS100BPP or URS150BPP model manufactured by Newport corporation may be used, the refractive index of the blazed grating medium is 1.514, the groove angle of the blazed grating is calibrated to be 30 °, and the blazed grating base material may be glass B270 manufactured by Schott corporation, for example.
On one side of the precision rotating platform 2, a line light source 3 is arranged at a certain distance from the rotating platform, and the minimum distance of the interval can be set as the distance that the line light source 3 does not interfere with the normal rotation of the precision rotating platform 2. The line light source 3 is used for providing light with a specific wavelength, the line light source 3 can adopt a metal vapor lamp, an air cathode lamp or a laser emitter, wherein the metal vapor lamp can be a mercury lamp or a sodium vapor lamp, the laser emitter can be selected at will, the laser emitter is selected to emit parallel light beams with a single wavelength in subsequent measurement of the application, and the wavelength of the laser is 632.8 nm.
The precise rotary table 2 is provided with a light detector 4 on one side opposite to the linear light source 3 and used for detecting the diffraction light energy of the monochromatic light passing through the blazed grating 1, preferably, a computer and a detector can be used together, the change of the diffraction light energy value of the precise rotary table 2 in the rotating process is monitored through the computer, so that the visual effect is more visual, the light detector 4 can be any one of a selenium light cell, a photodiode, a photomultiplier, a silicon diode array detector or a semiconductor detector, and in the application, a THORLABS optical power meter is selected to detect the diffraction light energy.
After the light path is built, the test is started according to the following steps:
step 1: as shown in fig. 2, a parallel light beam with a wavelength of 632.8nm emitted by a laser transmitter is made incident to the blazed grating 1 along the normal direction of the grating surface 11, and an initial angle K1 between a reference line and a zero position of the blazed grating 1 is made equal to 0 degree, and a light energy value Q1 of the line light source.
In this initial state, since the refractive index of air is equal to 1 in value, the refractive index of the substrate material of the blazed grating 1 is n, the groove angle is θ, L is the incident light, and L' is the direction of the maximum light intensity. Since the incident light is incident perpendicularly to the grating surface 11 of the blazed grating 1, the incident light is incident on the grating surface 11 of the blazed grating 1 from the air, and is still propagated in the direction of the incident light in the blazed grating 1 without changing the propagation direction. When the incident light is diffracted when it is incident on the scored facet 12, satisfying the grating equation, the light energy value Q1 of the line light source directly detected by the light detector 4 is 3.8 mW.
Step 2: as shown in fig. 3, the precision rotary table 2 is rotated while keeping the light source stationary, so that the precision rotary table 2 rotates the blazed grating 1 around the central axis, and the diffracted light energy emitted from the indented facet 12 is continuously detected, and when the blazed grating is recorded once every 1 ° rotation, and when the blazed grating is recorded every 1 ° rotation, an absolute value of a difference between two T values is ≧ 5%, the recording end angle K2 is determined, where the T values are: the diffracted light energy value for the current angle/the light energy value for the line light source. At this time, the incident angle on the scored facet 12 is just equal to the critical angle of total reflection formed by the substrate material of the blazed grating 1 and air, and the end angle K2 is recorded, during the rotation of the blazed grating, the data before and after the occurrence of total reflection is listed in table 1, the data of the diffracted light energy is recorded every time the blazed grating rotates 1 °, and as can be seen from the table, the values of K2 are all 16 ° in three parallel measurements;
table 1:
the T values in table 1 are: the diffracted light energy value/light energy value of the line light source for a current angle; z is the absolute value of the difference between the front and back T values when the blazed grating rotates by 1 degree.
In the above-mentioned ending state of rotation, as shown in fig. 3, the second incident angle formed on the scored facet 12 is exactly equal to the critical angle of total reflection formed by the blazed grating 1 and the air, where L is the incident light, L' is the refracted light when the incident light is emitted from the air to the base surface of the blazed grating 1, and L ″ is the total reflected light on the scored facet 12, where the first incident angle K incident on the grating surface 11 of the blazed grating 1 is the angle of rotation of the precision rotation stage 2, i.e., K is K2-K1, and in the specific calculation, since K1 is 0, K is numerically equal to K2, i is the refracted angle, and α is the second incident angle incident on the scored facet 12.
And step 3: calculating the groove angle theta of the blazed grating 1 according to the following formula:
where n is the refractive index of the substrate material of the blazed grating 1, K is K2-K1, and the calculated values are shown in table 2.
| n | Theta calibration value | K1 | K2 | k | Calculated value of theta | Error of the measurement |
| 1.514 | 30° | 0 | 16° | 16° | 30.85° | 2.8％ |
The error in table 2 is calculated as follows:
error is the difference between the calculated value of θ and the calibrated value of θ/calibrated value of θ.
The derivation of the slot angle calculation formula is described below with reference to the drawings. In the end state of the rotation, as shown in fig. 3, the incident light is refracted when it is incident from the air onto the grating surface 11 of the blazed grating 1. According to the snell law of refraction, the angle of refraction i is:
wherein n in the formula (1) is the refractive index of the substrate material of the blazed grating 1, k is the first incident angle, and the refractive index of air is 1.
As shown in fig. 3, according to the right triangle and the sum of three internal angles of the triangle being 180 degrees, the second incident angle α satisfies:
α＝i+θ......(2)
where θ is the slot angle.
According to the law of total reflection, the incident angle alpha formed by the facets 12 of the blazed grating 1 is exactly equal to the critical angle of total reflection formed by the substrate material of the blazed grating 1 and air. So that there are
Wherein n is the refractive index of the substrate material of the blazed grating 1.
The formula (2) is substituted by the above formula (1) and formula (3), and the calculation formula of the groove angle is obtained as follows:
as can be seen from the above detailed description, the method for measuring the slot angle described in the present application has the following advantages:
the groove angle measuring method can measure the groove angle without copying and slicing the blazed grating, has simple operation steps and cannot damage the transmission type plane blazed grating;
the measuring method of the groove angle has the advantages of simple measuring light path and low experimental requirement;
the method for measuring the groove angle is simple in principle, few in deduction steps, high in detection accuracy and only 2.8% in measurement error.
The above description is only for the specific embodiments of the present application, but the scope of the present application is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present disclosure should be covered within the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.
Claims (5)
1. A method for measuring the groove angle of a transmission type plane blazed grating is characterized by comprising the following steps:
enabling parallel light beams emitted by a linear light source to enter the blazed grating along the normal direction of the grating surface, and recording an initial angle K1 between a reference line and a zero position of the blazed grating at the moment and the light energy value of the linear light source; keeping a light source still, rotating the blazed grating along the central axis of the blazed grating, continuously detecting the diffraction light energy value emitted from the scored small plane of the blazed grating, and recording a termination angle K2 between a reference line and a zero position of the blazed grating when the absolute value of the difference value between two T values of the blazed grating which rotate by 1 degree is larger than or equal to 5%;
the central axis is the axis which is perpendicular to the normal of the grating surface and the normal of any scored small plane and penetrates through the blazed grating; the value of T is: the diffracted light energy value/light energy value of the line light source for a current angle;
calculating the blazed grating groove angle theta according to the following formula:
wherein n is a refractive index of the blazed grating substrate material, K is K2-K1,
the datum line is one of the following lines: the normal line of the grating surface of the blazed grating, the normal line of the indented facet, the extension line of the grating surface or the extension line of the indented facet;
before the test is started, a test light path is firstly established, a blazed grating to be tested is vertically arranged on a precise rotating platform, the central shaft of the blazed grating is superposed with the rotating axis of the precise rotating platform, and the precise rotating platform is provided with a zero position.
2. The method for measuring the groove angle of a transmissive blazed grating as claimed in claim 1, wherein the linear light source is a metal vapor lamp, an air cathode lamp, or a light source emitted from a laser emitter.
3. The method for measuring the groove angle of a transmissive blazed grating as claimed in claim 2, wherein the metal vapor lamp is a mercury lamp or a sodium vapor lamp.
4. The method for measuring the groove angle of a transmissive blazed grating as claimed in claim 2, wherein the laser transmitter emits light having a wavelength of 632.8 nm.
5. The method for measuring the groove angle of a transmissive blazed grating as claimed in claim 1, wherein the diffracted light energy is detected by one of the following optical detectors: a selenium photocell, a photodiode, a photomultiplier, a silicon diode array detector, an optical power meter, or a semiconductor detector.
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