CN116124420A - Method for measuring transmittance of high-reflection cavity mirror in optical cavity ring-down device based on wedge-shaped high-transmission optical element - Google Patents
Method for measuring transmittance of high-reflection cavity mirror in optical cavity ring-down device based on wedge-shaped high-transmission optical element Download PDFInfo
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Abstract
The invention discloses a method for measuring the transmittance of a high-reflection cavity mirror in an optical cavity ring-down device based on a wedge-shaped high-transmission optical element, which uses the wedge-shaped high-transmission optical element as a reference element, firstly measures the residual reflectance of the front surface or the rear surface of the wedge-shaped high-transmission optical element based on the optical cavity ring-down technology, then establishes a dual-channel optical cavity ring-down device for simultaneously measuring the output ring-down signals transmitted by the high-reflection cavity mirror and reflected by the known-reflectance surface of the wedge-shaped high-transmission optical element, simultaneously measures the output ring-down signals transmitted by the high-reflection cavity mirror and reflected by the known-reflectance surface of the wedge-shaped high-transmission optical element, calculates the ratio of the amplitude of the reflected optical cavity ring-down signal of the wedge-shaped high-transmission optical element to the amplitude of the optical cavity ring-down signal transmitted by the high-reflection cavity mirror to be measured, and realizes the accurate measurement of the transmittance of the high-reflection cavity mirror in the optical cavity ring-down device.
Description
Technical Field
The invention relates to the technical field of optical element parameter measurement, in particular to a high reflection cavity mirror transmittance measurement method.
Background
The high reflection cavity mirror is widely used in the technical fields of high-energy laser, gravitational wave detection, laser gyro and the like, and the accurate measurement of optical parameters is particularly necessary. Currently, high reflectance measurement is mainly based on cavity ring-down technology (Licheng, yuan; cavity ring-down high reflectance measurement review, progress in laser and optoelectronics, 2010, 47:021203), and accurate measurement of transmittance of high reflectance cavity mirrors is still a problem. Transmission to reflective optical elements at presentThe measurement of the transmittance still adopts a spectrophotometry technology, the invention patent of China patent application No. 201210524943.5 is a measurement method and a device of the transmittance of an optical element, and the invention patent of China patent application No. 201310013193.X is a measurement device and a measurement method of the transmittance of each optical component of an illumination system in a photoetching machine, and laser beams with specific wavelengths are split by a spectrophotometry to obtain two beams of light, and the two beams of light respectively pass through a reference light path and a test light path to measure the transmittance of the optical element. However, spectrophotometric techniques do not have sufficiently high measurement accuracy and require detectors of sufficiently large dynamic range (typically greater than 10 for measurements with highly reflective optical elements 5 ). Because of the limitation of the dynamic range of the detector, a fixed attenuation sheet is generally adopted as a reference sample to measure the transmittance of the high-reflection optical element, and the indirect measurement method enlarges the dynamic range, but also increases a reference sample, the transmittance of the reference sample is still measured by a spectrophotometry technology, and the measurement error of the reference sample can lead to the measurement error of the transmittance of the high-reflection optical element.
In addition, in the invention patent of chinese patent application No. 201610972470.3, "a method for simultaneously measuring the reflectivity and transmittance of the high reflection/high transmission optical element based on the cavity ring-down technique", and the invention patent of chinese patent application No. 201710332425.6, "a method for simultaneously measuring the reflectivity, transmittance, scattering loss and absorption loss of the high reflection/high transmission optical element", in order to simultaneously accurately measure the reflectivity, transmittance, scattering loss and absorption loss of the high reflection/high transmission optical element, it is necessary to accurately measure the transmittance of the high reflection output cavity mirror in advance. Based on the measurement requirement, the 'calibration method of high reflection cavity lens transmittance' of the patent application No. 201710332421.8 proposes to measure the transmittance of the high reflection cavity lens by using a planar high transmission optical element based on the cavity ring-down technology, but because interference effects may occur between reflected laser beams on the front and rear surfaces of the planar high transmission optical element, the accuracy of the high reflection cavity lens transmittance measurement result will be seriously affected, so that the accuracy of the reflectivity, transmittance, scattering loss and absorption loss of the high reflection/high transmission optical element is further affected.
Disclosure of Invention
The invention aims to solve the technical problems that: in order to overcome the defects in the prior art, the method for measuring the transmittance of the high-reflection cavity mirror in the optical cavity ring-down device based on the wedge-shaped high-transmission optical element is provided, the wedge-shaped high-transmission optical element is used as a reference sample, the residual reflectivity of the front surface and/or the rear surface of the wedge-shaped high-transmission optical element is accurately measured by an optical cavity ring-down technology, and then the transmittance of the high-reflection cavity mirror to be measured is obtained by measuring the amplitude ratio of an optical cavity ring-down signal transmitted from the high-reflection cavity mirror to be measured to an optical cavity ring-down signal reflected from the front surface or the rear surface of the wedge-shaped high-transmission optical element respectively.
The implementation steps are as follows:
the method comprises the steps of (1) establishing an optical cavity ring-down measuring device based on a straight cavity or a folding cavity, wherein an output cavity mirror of the optical cavity ring-down measuring device is composed of a high-reflection cavity mirror to be measured, and an optical cavity ring-down signal is obtained by detecting the laser beam intensity time characteristic transmitted by the high-reflection cavity mirror to be measured by adopting a first photoelectric detector; firstly measuring ring-down time of initial optical resonant cavity, then inserting wedge-shaped high-transmission optical element to form test optical resonant cavity, regulating angle of wedge-shaped high-transmission optical element to make laser beams reflected by front and rear surfaces of wedge-shaped high-transmission optical element respectively coincide with laser beams in the cavity, and making the laser beams reflected by front and rear surfaces respectively be emitted out of optical resonant cavity, measuring ring-down time of test optical resonant cavity under the correspondent three conditions, calculating to obtain front surface reflectivity R of wedge-shaped high-transmission optical element f And back surface reflectivity R r ；
Step (2), adjusting the angle of the wedge-shaped high-transmission optical element to enable front and rear reflection light beams to be emitted out of the test optical resonant cavity, adopting a second photoelectric detector to detect the time characteristic of the intensity of the laser beam reflected by the front surface or the rear surface of the wedge-shaped high-transmission optical element, and simultaneously recording the ring-down signals of the optical cavity obtained by the first photoelectric detector and the second photoelectric detector;
step (3), fitting the cavity ring-down signals obtained by the first and second photodetectors recorded in the step (2) according to a single exponential function, wherein the fitted expressions are respectively
(A 11 ，A 12 Constant coefficient, t is time) and
(A 21 ，A 22 constant coefficients), respectively obtain the amplitude A of the cavity ring-down signal transmitted from the measured high reflection cavity mirror 11 And ring down time τ 1 And amplitude A of cavity ring-down signal reflected from front or back surface of wedge-shaped high transmission optical element 21 And ring down time τ 2 ；
Step (4), calculating (τ) 2 -τ 1 )/(τ 2 +τ 1 ) When the absolute value is less than 5%, the transmittance of the high-reflection cavity mirror to be measured is obtained through the following formula: (1) When the second photodetector detects the cavity ring-down signal reflected by the front surface of the wedge-shaped highly transmissive optical element, t=m× (a 11 /A 21 )×R f The method comprises the steps of carrying out a first treatment on the surface of the (2) When the second photodetector detects the cavity ring-down signal reflected by the rear surface of the wedge-shaped highly transmissive optical element, t=m× (a 11 /A 21 )×R r Wherein M is the magnification ratio of the second detector to the first detector.
Wherein the wedge angle of the wedge-shaped high-transmission optical element is in the range of 0.5-3 degrees.
The antireflection film of the wedge-shaped high-transmission optical element is a broadband antireflection film, the residual reflectivity of the front surface and the rear surface of the antireflection film is between 0.0001% and 0.1%, and the variation of the residual reflectivity of the antireflection film is not more than +/-3% within the range of an incident angle of +/-5 degrees;
wherein, the detector magnification ratio M of the step (2) is obtained by the following method: the same stable optical signal is measured by a first and a second photo detector, respectively, and the ratio of the measurement results of the second and the first photo detector is M.
Compared with the prior art, the invention has the following technical advantages: the invention adopts the wedge-shaped high-transmission optical element as a reference sample, and the residual reflectivity of the front surface and/or the rear surface of the wedge-shaped high-transmission optical element can be very accurately measured by an optical cavity ring-down technology because the influence of the laser beam interference reflected by the front surface and the rear surface is eliminated; meanwhile, the method is based on the wedge-shaped high-transmission optical element and the dual-channel cavity ring-down technology to measure the transmittance of the high-reflectivity cavity mirror, so that the influence of interference effect is eliminated, and the measurement accuracy of the transmittance of the high-reflectivity cavity mirror is further improved.
Drawings
FIG. 1 is a schematic diagram of a high reflection cavity mirror transmittance measurement in a cavity ring-down device based on reflection from the front surface of a wedge-shaped high transmission optical element in accordance with the present invention;
FIG. 2 is a schematic diagram of a high reflection cavity mirror transmittance measurement in a cavity ring-down device based on the reflection of the front surface of a wedge-shaped high transmission optical element according to the present invention.
In fig. 1 and 2: 1 is a laser light source; 2 is a plane high reflection cavity mirror; 3 is a high reflection cavity mirror to be measured; 4 is a plano-concave high reflection cavity mirror; 5 is a wedge-shaped high transmission optical element; 6 and 8 are focusing lenses; 7 is a first photoelectric detector, 9 is an adjustable aperture diaphragm, and 10 is a second photoelectric detector; 11 is a function generating card; 12 is a data acquisition card; 13 is a computer; wherein the thick line in the figure is the light path, and the thin line is the connecting line.
FIG. 3 is a graph of cavity ring-down signals detected by first and second photodetectors recorded simultaneously
Detailed Description
A method of measuring the transmittance of a highly reflective cavity mirror of the present invention is described below in connection with the configuration of measuring the transmittance of a highly reflective cavity mirror in a cavity ring-down device based on the reflection of the front and/or rear surfaces of a wedge-shaped highly transmissive optical element as described in connection with fig. 1 and 2. It is to be understood, however, that the drawings are designed solely for the purposes of providing a better understanding of the invention and are not to be construed as limiting the invention.
The light source 1 is a continuous semiconductor laser, and square wave synchronous modulation output of the function generating card 11 is adopted; according to the optical feedback cavity ring down technique, laser light is injected into a stable optical resonator. The stable initial optical resonant cavity is formed by a plane high reflection mirror 2, a high reflection cavity mirror 3 to be tested and a plano-concave high reflection mirror 4. The incident laser beam is injected into the optical resonator through the plane high reflection mirror 2 and oscillates in the resonator. At the falling edge of square waveThe laser is turned off to generate a ring-down signal, and the ring-down signal recorded by the first photodetector 7 is fitted to the ring-down time of the initial optical resonator according to a single exponential decay function. The wedge-shaped high-transmission optical element 5 is inserted into the initial optical resonant cavity to form a stable test optical resonant cavity, the wedge angle range of the wedge-shaped high-transmission optical element is 0.5-3 degrees, the front surface and the rear surface are plated with broadband antireflection films, the residual reflectivity is between 0.0001% and 0.1%, and the variation of the residual reflectivity is not more than +/-3% within the incident angle range of +/-5 degrees. The method for measuring the residual reflectivity R of the front surface of the wedge-shaped high-transmission optical element is obtained according to the measuring steps described in the patent application No. 202211383206.8 of Chinese patent application f And residual reflectivity R of rear surface r . And then adjusting the angle of the wedge-shaped high-transmission optical element to enable the laser beams reflected by the front surface and the rear surface of the wedge-shaped high-transmission optical element to be emitted out of the optical resonant cavity, and ensuring that the incidence angles of the laser beams in the cavity to the front surface and the rear surface are within a range of +/-5 degrees. The cavity ring-down signal reflected from the front or back surface of the wedge-shaped high transmission optical element is detected by a second photodetector 10 using an adjustable aperture stop 8 to selectively reflect the laser beam through the front surface (FIG. 1) or the back surface (FIG. 2) and as a single exponential function
(A 21 ，A 22 For a constant coefficient, t is time) to fit the signal amplitude A 21 And ring down time τ 2 Simultaneously recording cavity ring-down signal transmitted from the measured high reflection cavity mirror detected by the first photodetector 7 according to a single exponential function +.>
(A 11 ，A 12 For a constant coefficient, t is time) to fit the signal amplitude A 11 And ring down time τ 1 The cavity ring down signal recorded simultaneously is shown in fig. 3. Calculation (τ) 2 -τ 1 )/(τ 2 +τ 1 ) When the absolute value is less than 5%, the transmittance of the high-reflection cavity mirror to be measured is obtained through the following formula: (1) When the second photoelectric probeThe detector detects the cavity ring-down signal reflected by the front surface of the wedge-shaped high transmission optical element, where t=mx (a 11 /A 21 )×R f The method comprises the steps of carrying out a first treatment on the surface of the (2) When the second photodetector detects the cavity ring-down signal reflected by the rear surface of the wedge-shaped highly transmissive optical element, t=m× (a 11 /A 2 1)×R r Where M is the ratio of the amplification of the second and first detectors, and can be obtained by measuring the same stable optical signal using two photodetectors.
In a word, the invention provides a measuring method of the transmittance of the high reflection cavity mirror in the optical cavity ring-down device based on the wedge-shaped high transmission optical element, which adopts the wedge-shaped high transmission optical element as a reference sample, eliminates the influence of the interference of the reflected laser beams on the front surface and the rear surface of the reference sample on the measuring result, and greatly improves the measuring precision of the transmittance of the high reflection cavity mirror.
Claims (4)
1. A measuring method of high reflection cavity mirror transmissivity in an optical cavity ring-down device based on a wedge-shaped high transmission optical element comprises the following implementation steps:
the method comprises the steps of (1) establishing an optical cavity ring-down measuring device based on a straight cavity or a folding cavity, wherein an output cavity mirror of the optical cavity ring-down measuring device is composed of a high-reflection cavity mirror to be measured, and an optical cavity ring-down signal is obtained by detecting the laser beam intensity time characteristic transmitted by the high-reflection cavity mirror to be measured by adopting a first photoelectric detector; firstly measuring ring-down time of initial optical resonant cavity, then inserting wedge-shaped high-transmission optical element to form test optical resonant cavity, regulating angle of wedge-shaped high-transmission optical element to make laser beams reflected by front and rear surfaces of wedge-shaped high-transmission optical element respectively coincide with laser beams in the cavity, and making the laser beams reflected by front and rear surfaces respectively be emitted out of optical resonant cavity, measuring ring-down time of test optical resonant cavity under the correspondent three conditions, calculating to obtain front surface reflectivity R of wedge-shaped high-transmission optical element f And back surface reflectivity R r ；
Step (2), adjusting the angle of the wedge-shaped high-transmission optical element to enable the reflected light beams on the front surface and the rear surface of the wedge-shaped high-transmission optical element to be emitted out of the test optical resonant cavity, adopting a second photoelectric detector to detect the time characteristic of the intensity of the laser beam reflected by the front surface or the rear surface of the wedge-shaped high-transmission optical element, and simultaneously recording the ring-down signals of the optical cavity detected by the first photoelectric detector and the second photoelectric detector;
step (3), fitting the cavity ring-down signals obtained by the first and second photodetectors recorded in the step (2) according to a single exponential function, wherein the fitted expressions are respectively
(A 11 ，A 12 Constant coefficient, t is time) and
(A 21 ，A 22 constant coefficients), respectively obtain the amplitude A of the cavity ring-down signal transmitted from the measured high reflection cavity mirror 11 And ring down time τ 1 And amplitude A of cavity ring-down signal reflected from front or back surface of wedge-shaped high transmission optical element 21 And ring down time τ 2 ；
Step (4), calculating (τ) 2 -τ 1 )/(τ 2 +τ 1 ) When the absolute value is less than 5%, the transmittance of the high-reflection cavity mirror to be measured is obtained through the following formula: (1) When the second photodetector detects the cavity ring-down signal reflected by the front surface of the wedge-shaped highly transmissive optical element, t=m× (a 11 /A 21 )×R f The method comprises the steps of carrying out a first treatment on the surface of the (2) When the second photodetector detects the cavity ring-down signal reflected by the rear surface of the wedge-shaped highly transmissive optical element, t=m× (a 11 /A 21 )×R r Wherein M is the magnification ratio of the second detector to the first detector.
2. The method for measuring the transmittance of a high reflection cavity mirror in an optical cavity ring-down device based on a wedge-shaped high transmission optical element according to claim 1, wherein the method comprises the steps of: the wedge angle of the wedge-shaped high-transmission optical element is in the range of 0.5-3 degrees.
3. The method for measuring the transmittance of a high reflection cavity mirror in an optical cavity ring-down device based on a wedge-shaped high transmission optical element according to claim 1, wherein the method comprises the steps of: the wedge-shaped high-transmission optical element is plated with a broadband antireflection film, the residual reflectivity of the front surface and the rear surface of the wedge-shaped high-transmission optical element is between 0.0001% and 0.1%, and the variation of the residual reflectivity is not more than +/-3% within the range of an incident angle of +/-5 degrees.
4. The method for measuring the transmittance of a high reflection cavity mirror in an optical cavity ring-down device based on a wedge-shaped high transmission optical element according to claim 1, wherein the method comprises the steps of: the detector magnification ratio M of the step (2) is obtained by the following method: the same stable optical signal is measured by a first and a second photo detector, respectively, and the ratio of the measurement results of the second and the first photo detector is M.
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