CN102128715B - Method for measuring reflectivity of dual-wavelength high reflecting mirror - Google Patents

Method for measuring reflectivity of dual-wavelength high reflecting mirror Download PDF

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CN102128715B
CN102128715B CN2010105930935A CN201010593093A CN102128715B CN 102128715 B CN102128715 B CN 102128715B CN 2010105930935 A CN2010105930935 A CN 2010105930935A CN 201010593093 A CN201010593093 A CN 201010593093A CN 102128715 B CN102128715 B CN 102128715B
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high reflection
reflection mirror
dual wavelength
optical resonator
wavelength high
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CN102128715A (en
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李斌成
曲哲超
韩艳玲
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Institute of Optics and Electronics of CAS
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Institute of Optics and Electronics of CAS
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Abstract

The invention discloses a method for measuring the reflectivity of a dual-wavelength high reflecting mirror. The method comprises the following steps: injecting the continuous lasers of two different wavelengths with periodically modulated light intensity into a stable initial optical resonance cavity composed of two or three dual-wavelength high reflecting mirrors at the same time; when the amplitude of the output signal of the initial optical resonance cavity is higher than a set threshold, cutting off the incident laser beam and recording the cavity ring-down signal; or recording the cavity ring-down signal at the falling edge of a modulation signal, and obtaining the ring-down time [tau]01 and [tau]02 of the initial optical resonance cavity at the two laser wavelengths by use of a synchronous measurement method, spectral detection method or alternate measurement method, and calculating the average reflectivity R01 and R02 of a cavity mirror at the two wavelengths; similarly, adding a dual-wavelength high reflecting mirror to be measured into the initial optical resonance cavity according to the using angle so as to form a stable test optical resonance cavity; obtaining the ring-down time [tau]01 and [tau]02 of the test optical resonance cavity at the two laser wavelengths by use of a synchronous measurement method, spectral detection method or alternate measurement method; and obtaining the reflectivity R1 and R2 of the dual-wavelength high reflecting mirror to be measured at the two wavelengths.

Description

Dual wavelength high reflection mirror method for measuring reflectance
Technical field
The present invention relates to a kind of method and apparatus that is used to measure the high reflection mirror reflectivity, particularly a kind of method of measuring dual wavelength high reflection mirror reflectivity.
Background technology
In recent years, the high reflectivity film optical element has obtained application more and more widely in fields such as large laser system, laser gyro, gravitational wave measurement and trace gas detections.And the optical cavity ring-down technology is accurately to measure main method (Li Bincheng, the Gong Yuan of high reflection mirror reflectivity at present; Optical cavity ring-down high reflection rate measurement summary, " laser and optoelectronics progress ", 2010,47:021203).The patent of invention " a kind of measuring method of high reflective mirror high reflectance " of one Chinese patent application numbers 98114152.8; Adopt pulse laser system to make light source; The shortcoming of this method is: since pulsed laser beam of poor quality, decline and swing factors such as there being mode competition in the chamber, measuring accuracy is limited by, and employed pulsed laser cost is high; Improved system cost, be unfavorable for promoting the use of.The patent of invention " a kind of measuring method of reflectance ratio of high reflected mirror " of one Chinese patent application numbers 200610011254.9 has proposed a kind of high reflectivity measurement method of making light source with the continuous semiconductor laser instrument; But the optical cavity output signal that adopts the phase-lock mode detection to aspire for stability; It is low that laser power is coupled into the efficient of swinging the chamber of declining; After the cavity mirrors reflectivity height arrived to a certain degree, the optical cavity output amplitude reduced, and signal to noise ratio (S/N ratio) descends; Make device regulate relatively difficulty, and limited and to have surveyed high reflectance and measuring accuracy.The patent of invention " a kind of device that is used to measure high reflectance " of the patent of invention " based on the high reflectivity measurement method of frequency selective optical feedback cavity ringdown spectroscopy " of the patent of invention " measuring method of reflectance ratio of high reflected mirror " of one Chinese patent application numbers 200610165082.0, the patent of invention " high reflectivity measurement method of based semiconductor self-mixing effect " of one Chinese patent application 200710098755.X, one Chinese patent application numbers 200810102778.8 and one Chinese patent application numbers 200810055635.4 is all used the continuous optical cavity oscillation method that declines; Continuous laser swings chamber optical axis incident along declining; When optical cavity ring-down signal amplitude during greater than preset threshold; Laser beam is closed in triggering; Record optical cavity ring-down signal; Perhaps at modulated square wave negative edge record optical cavity ring-down signal; Utilize the single index attenuation function to simulate ring-down time the signal that obtains, and then obtain the albedo measurement result.
Above-mentioned measuring method all can only be measured the reflectivity of high reflection mirror at the single wavelength place with device, can not record the reflectivity of dual wavelength high reflection mirror in two wavelength simultaneously.Along with the continuous expansion that the development and the laser system of laser technology are used, dual wavelength or multi-wavelength high reflection mirror are used also day by day extensive in many laser systems.Demand to dual wavelength and multiwavelength laser source also constantly increases in many optical systems at present; For example; The patent of invention " multiple wavelength laser system " of one Chinese patent application numbers 200510077804.2, wherein the dual wavelength of laser resonant cavity chamber mirror even multi-wavelength albedo measurement are very necessary.
Summary of the invention
The technical matters that the present invention will solve is: overcome the deficiency of existing single wavelength high reflection mirror albedo measurement technology, proposed a kind of dual wavelength high reflection mirror method for measuring reflectance based on the optical cavity ring-down technology, have measure highly sensitive, the advantage of easy operating.
The technical solution adopted for the present invention to solve the technical problems is: dual wavelength high reflection mirror method for measuring reflectance, and performing step is following:
(1) continuous laser with two different wave lengths of light intensity periodic modulation incides the initial optical resonator cavity simultaneously;
Said initial optical resonator cavity is placed perpendicular to optical axis relatively by two identical plano-concave dual wavelength high reflection mirror concave surfaces and is formed, and incident light impinges perpendicularly on second plano-concave dual wavelength high reflection mirror after seeing through from first plano-concave dual wavelength high reflection mirror center;
Or the initial optical resonator cavity is made up of two identical plano-concave dual wavelength high reflection mirrors and a plane dual wavelength high reflection mirror; The plane high reflection mirror is incident chamber mirror and favours the optical axis placement; Incoming laser beam impinges perpendicularly on first plano-concave high reflection mirror placing perpendicular to optical axis after this plane high reflection mirror transmission; Laser beam is back to the plane high reflection mirror by first plano-concave high reflection mirror reflection back by former road; Again by plane high reflection mirror secondary reflection again, reflected light impinges perpendicularly on second plano-concave high reflection mirror then;
(2) two different wavelength of laser from two dual wavelength high reflection mirrors transmission of said initial optical resonator cavity focus on photodetector by condenser lens; Photodetector is surveyed the optical cavity ring-down signal of initial optical resonator cavity; When the optical cavity ring-down signal amplitude of initial optical resonator surpasses setting threshold; Trigger and turn-off incoming laser beam; Write down the optical cavity ring-down signal of initial optical resonator cavity, perhaps write down the optical cavity ring-down signal of initial optical resonator cavity, utilize simultaneous measurement method or divide optical probe method or replace mensuration to obtain the ring-down time τ of initial optical resonator cavity in two laser wave strong points at the negative edge of modulation signal 01, τ 02, and then obtain the average reflectance R of dual wavelength high reflective cavity mirror in two wavelength 01, R 02
(3) use angle according to dual wavelength high reflection mirror to be measured adds dual wavelength high reflection mirror to be measured in the initial optical resonator cavity, constitutes the measuring optical resonator cavity;
Constituting of said measuring optical resonator cavity: incident light first plano-concave dual wavelength high reflection mirror center from the initial optical resonator cavity gets into; Keep first plano-concave dual wavelength high reflection mirror position motionless; Between two plano-concave dual wavelength high reflection mirrors, add dual wavelength high reflection mirror to be measured; Laser beam incides dual wavelength high reflection mirror to be measured after seeing through first plano-concave dual wavelength high reflection mirror; Incident angle is a dual wavelength high reflection mirror use angle, and the position that changes second plano-concave dual wavelength high reflection mirror makes from dual wavelength high reflection mirror laser light reflected bundle to be measured and impinges perpendicularly on second plano-concave dual wavelength high reflection mirror, constitutes the measuring optical resonator cavity;
Or the constituting of measuring optical resonator cavity: plane dual wavelength high reflection mirror is incident chamber mirror and favours optical axis and place; Incoming laser beam impinges perpendicularly on first plano-concave dual wavelength high reflection mirror placing perpendicular to optical axis after this plane dual wavelength high reflection mirror transmission; Laser beam is back to plane dual wavelength high reflection mirror by first plano-concave dual wavelength high reflection mirror reflection back by original optical path; Again by plane dual wavelength high reflection mirror secondary reflection again, reflected light impinges perpendicularly on second plano-concave dual wavelength high reflection mirror then; Between second plano-concave dual wavelength high reflection mirror of initial optical resonator cavity and plane dual wavelength high reflection mirror, insert dual wavelength high reflection mirror to be measured; After incoming laser beam sees through plane dual wavelength high reflection mirror; Successively through behind first plano-concave dual wavelength high reflection mirror and the plane dual wavelength high reflection mirror; Incide dual wavelength high reflection mirror to be measured; Incident angle is a dual wavelength high reflection mirror use angle to be measured, impinges perpendicularly on second plano-concave dual wavelength high reflection mirror from dual wavelength high reflection mirror laser light reflected bundle to be measured, constitutes the measuring optical resonator cavity;
(4) two different wavelength of laser from the transmission of output dual wavelength high reflective cavity mirror focus on photodetector by condenser lens; Photodetector is surveyed the optical cavity ring-down signal; When measuring optical resonator cavity output signal amplitude surpasses setting threshold; Trigger and turn-off incoming laser beam; Write down the optical cavity ring-down signal of measuring optical resonator cavity, perhaps write down the optical cavity ring-down signal of measuring optical resonator cavity, utilize simultaneous measurement method or divide optical probe method or replace mensuration to obtain the ring-down time τ of measuring optical resonator cavity in two laser wave strong points at the negative edge of modulation signal 1, τ 2, through calculating the reflectivity R of dual wavelength high reflection mirror to be measured in two wavelength 1, R 2
Described two continuous lasers are by semiconductor laser or solid state laser or gas laser generation.
The reflectivity of the plano-concave dual wavelength high reflection mirror of described initial optical resonator cavity and measuring optical resonator cavity and plane dual wavelength high reflection mirror in two wavelength all greater than 99%.
Described initial optical resonator cavity and measuring optical resonator cavity are stable cavity or confocal resonator, and total long L in chamber satisfies 0＜L≤2r, and wherein r is the radius-of-curvature of plano-concave dual wavelength high reflection mirror concave surface.
Trigger in said step (2) and (4) and turn-off two incoming laser beams and realize one of in the following manner:
When a. adopting the continuous semiconductor laser instrument, when initial optical resonator or measuring optical resonator cavity output signal amplitude is higher than setting threshold, quick closedown semiconductor laser exciting current or voltage;
When b. adopting continuous semiconductor laser instrument or solid state laser or gas laser; When initial optical resonator or measuring optical resonator cavity output signal amplitude is higher than setting threshold, between laser instrument and incident dual wavelength high reflective cavity mirror, adopt fast optical switch based to close laser beam;
C. adopt the square-wave frequency modulation fast optical switch based, or during square-wave frequency modulation laser instrument excitation power supply, when initial optical resonator or measuring optical resonator cavity output signal amplitude are higher than setting threshold, utilize the square wave negative edge to close laser beam.
The optical cavity ring-down signal of the initial optical resonator cavity in the said step (2) is by oscillograph or data collecting card record.
Described simultaneous measurement method obtains the reflectivity R of dual wavelength high reflection mirror to be measured in two wavelength 1, R 2Implementation procedure following: the optical cavity ring-down signal of the initial optical resonator cavity of record in the step (2) press double-exponential function decays,
Figure BSA00000389457100041
Δ t is poor for the two laser turn-off time, A 01, A 02, A 03Be constant coefficient, utilize the match of multi-parameter fitting program to obtain the ring-down time τ of initial optical resonator cavity in two laser wave strong points 01, τ 02Equally, under measuring optical resonator cavity situation, the optical cavity ring-down signal of the measuring optical resonator cavity of record in the step (4) is pressed the double-exponential function decay,
Figure BSA00000389457100042
A 11, A 12, A 13Be constant coefficient, utilize the match of multi-parameter fitting program to obtain the ring-down time τ of measuring optical resonator cavity in two laser wave strong points 1, τ 2, according to formula
Figure BSA00000389457100043
With L wherein 0For initial optical resonator cavity chamber long, L 1Long for measuring optical resonator cavity chamber, calculate the reflectivity R of dual wavelength high reflection mirror to be measured in two wavelength 1, R 2
Optical probe method obtained the reflectivity R of dual wavelength high reflection mirror to be measured in two wavelength in said minute 1, R 2Implementation procedure following: with initial optical resonator cavity output signal in the step (2) through the beam splitter beam split; Two different wavelength of laser are focused on different photodetectors respectively, and the optical cavity ring-down signal that two photodetectors record is respectively by single index attenuation function I (t)=Ae -t/ τ+ B, A wherein, B is a constant coefficient, simulates the ring-down time τ of initial optical resonator cavity in two laser wave strong points 01, τ 02Equally; Under measuring optical resonator cavity situation; Measuring optical resonator cavity in the step (4) is exported signal through the beam splitter beam split, and two different wavelength of laser are focused on different photodetectors respectively, and the optical cavity ring-down signal that two photodetectors record is respectively by single index attenuation function I (t)=A 1e -t/ τ+ B 1, A wherein 1, B 1Be constant coefficient, simulate the ring-down time τ of measuring optical resonator cavity in two laser wave strong points 1, τ 2, according to formula
Figure BSA00000389457100045
With
Figure BSA00000389457100046
L wherein 0For initial optical resonator cavity chamber long, L 1Long for measuring optical resonator cavity chamber, calculate the reflectivity R of dual wavelength high reflection mirror to be measured in two wavelength 1, R 2
Said alternately mensuration obtains the reflectivity R of dual wavelength high reflection mirror to be measured in two wavelength 1, R 2Implementation procedure following: adopt mechanical shutter or electric switch method alternately to close two laser; In the process of measuring, earlier a long wavelength laser cuts out or this Laser Output Beam is blocked, the initial optical resonator cavity of record in the step (2) is pressed the single index attenuation function at the optical cavity ring-down signal of another wavelength
Figure BSA00000389457100047
Simulate ring-down time τ 01, A wherein 01, B 01Be constant coefficient; Close or block another wavelength laser bundle then, the optical cavity ring-down signal of the laser wave strong point that the initial optical resonator cavity of record in the step (2) formerly is closed or blocks is by the single index attenuation function
Figure BSA00000389457100048
Simulate ring-down time τ 02, A wherein 02, B 02Be constant coefficient; Equally, under measuring optical resonator cavity situation, earlier a long wavelength laser cuts out or this Laser Output Beam is blocked, the measuring optical resonator cavity of record in the step (4) is pressed the single index attenuation function at the optical cavity ring-down signal of another wavelength
Figure BSA00000389457100049
Simulate ring-down time τ 1, A wherein 11, B 11Be constant coefficient; Close or block another wavelength laser bundle then, the optical cavity ring-down signal of the laser wave strong point that the measuring optical resonator cavity of record in the step (4) formerly is closed or blocks is by the single index attenuation function
Figure BSA00000389457100051
Simulate ring-down time τ 2, A wherein 12, B 12Be constant coefficient, according to formula
Figure BSA00000389457100052
With
Figure BSA00000389457100053
L wherein 0For initial optical resonator cavity chamber long, L 1Long for measuring optical resonator cavity chamber, calculate the reflectivity R of dual wavelength high reflection mirror to be measured in two wavelength 1, R 2
Described fast optical switch based is electrooptical modulation switch or acoustooptic modulation switch.
Described beam splitter is grating or prism.
Described method for measuring reflectance also can be used for three-wavelength or multi-wavelength high reflection mirror albedo measurement more.
Said photodetector can be three or more single-element detector, also can be the high-speed photodetector of a linear array.
The present invention compared with prior art has following advantage: the present invention utilizes optical cavity ring-down commercial measurement dual wavelength high reflection mirror reflectivity; Can obtain the reflectivity of high reflection mirror simultaneously in two wavelength; Also can be used for the measurement of single wavelength high reflection mirror reflectivity, realize dual-use or use more.The present invention adopts the optical cavity ring-down technology based on optical feedback effect, has greatly improved the amplitude of output signal, so the gained signal has high s/n ratio, has improved measuring accuracy, and this method also has simple to operate, low cost and other advantages.
Description of drawings
Fig. 1 is a kind of initial optical resonator cavity measurement mechanism synoptic diagram of the present invention, in this embodiment, adopts square-wave frequency modulation semiconductor laser excitation power supply, turn-offs laser beam at the square wave negative edge;
Fig. 2 is a kind of initial optical resonator cavity measurement mechanism synoptic diagram of the present invention, in this embodiment, adopts fast optical switch based to turn-off laser beam;
Fig. 3 is the structural representation of a kind of measuring optical resonator cavity of the present invention;
Fig. 4 is the measurement mechanism synoptic diagram of of the present invention minute optical probe method;
Fig. 5 is a kind of initial optical resonator cavity measurement mechanism synoptic diagram of the present invention, in this embodiment, adopts mechanical shutter or wavelength-selective switches alternately to turn-off two laser;
Fig. 6 is the structural representation of frequency selectivity light feedback initial optical resonator cavity of the present invention;
Fig. 7 is the structural representation of frequency selectivity light feedback test optical resonator of the present invention.
Embodiment
The measuring method of dual wavelength high reflection mirror reflectivity of the present invention is described below in conjunction with accompanying drawing 1 described measuring system.Among Fig. 1: 1; 2 be respectively two different wavelength of laser light sources, 3 for catoptron, 4 for the twin-beam spectroscope, 5 and 6 for plano-concave dual wavelength high reflection mirror, 7 for condenser lens, 8 for photodetector, 9 for computing machine, 10 for data collecting card, 11 for function block, 12 for visible auxiliary alignment light source, 13 be that spectroscope, 14 is a catoptron; Thick line is a light path among the figure, and fine rule is a connecting line.
Light source 1,2 is all selected the continuous semiconductor laser instrument for use, and two semiconductor lasers adopt square-wave frequency modulation output; Through catoptron 3 and twin-beam spectroscope 4 two laser is closed bundle, make it inject simultaneously to decline and swing the chamber; Greater than 99%, declining and swinging the chamber is stable optical resonator cavity or confocal optical resonator at two-laser wavelength reflectivity for two plano-concave dual wavelength high reflection mirrors 5,6, and the long L in chamber satisfies 0＜L≤2r, and wherein r is the radius-of-curvature of plano-concave dual wavelength high reflection mirror concave surface; Two plano-concave dual wavelength high reflection mirrors are placed perpendicular to light path; And laser beam is passed through from the minute surface center, and laser beam gets into optical resonator from first plano-concave dual wavelength high reflection mirror, along with the injection of laser beam; The optical resonator self-energy increases gradually; Have no progeny when the incoming laser beam quilt closes rapidly, luminous energy can reduce owing to chamber mirror transmission gradually in the optical resonator, and the part laser energy is exported from second plano-concave dual wavelength high reflection mirror; Focus on photodetector 8 from the laser beam of optical resonator Effect of Back-Cavity Mirror transmission by condenser lens 7, photodetector 8 output signals are by data collecting card 10 records and 9 storages of input computing machine and processing.Because light source 1; 2 all adopt function that the output of card 11 square wave synchronous modulation takes place; Turn-offed fast in square wave falling edge laser beam, when optical resonator output signal amplitude at the square wave falling edge during greater than pre-set threshold, computing machine 9 control data capture cards 10 are gathered to decline and are swung signal.Visible light source 12, spectroscope 13 and catoptron 14 are used for the auxiliary adjustment light path.When having one or two to be visible light source in light source 1 and 2, can not use the auxiliary adjustment light path.Utilize the multi-parameter fitting program according to two decaying exponential functions the signal of data collecting card 10 record:
Figure BSA00000389457100061
(Δ t is poor for the two laser turn-off time, and Δ t is much smaller than ring-down time usually, and it is several to up to a hundred nanoseconds that Δ t is generally, A 01, A 02, A 03Be constant coefficient, in the multi-parameter fitting process, be made as free parameter, simulate the ring-down time τ of initial optical resonator cavity in two laser wave strong points 01, τ 02According to formula
Figure BSA00000389457100062
L wherein 0Long for the initial cavity optical resonator, c is the light velocity, can get the average reflectance R of dual wavelength high reflective cavity mirror in two wavelength 01, R 02
The shutoff of laser beam also can realize through fast optical switch based among the present invention, and is as shown in Figure 2. Light source 1,2 adopts continuous semiconductor laser instrument or solid state laser or gas laser, between laser instrument and incident chamber mirror, adds fast optical switch based 15, is controlled by computing machine 9.When the optical resonator that collects is exported signal amplitude greater than threshold value (setting threshold is about the 80%-90% of maximum signal amplitude value usually), trigger photoswitch 15 and close.
Be illustrated in figure 3 as and add the measuring optical resonator cavitys that dual wavelength high reflection mirror to be measured 16 backs constitute, but measurement of reflectivity is greater than the reflectivity under the different incidence angles of 99% plane dual wavelength high reflection mirror.Keep first plano-concave dual wavelength high reflection mirror position motionless; Between two plano-concave dual wavelength high reflection mirrors, add dual wavelength high reflection mirror to be measured; Laser beam incides dual wavelength high reflection mirror to be measured after seeing through first plano-concave dual wavelength high reflection mirror; Incident angle is a dual wavelength high reflection mirror use angle, and the reflected light of dual wavelength high reflection mirror impinges perpendicularly on second plano-concave dual wavelength high reflection mirror, constitutes stable measuring optical resonator cavity.When the measuring optical resonator cavity was exported signal amplitude greater than pre-set threshold, computing machine 9 control data capture cards 10 were gathered to decline and are swung signal.Utilize the multi-parameter fitting program according to two decaying exponential functions:
Figure BSA00000389457100071
(Δ t is poor for the two laser turn-off time, and usually Δ t is much smaller than ring-down time, A 11, A 12, A 13Be constant coefficient, in the multi-parameter fitting process, be made as free parameter) simulate the ring-down time τ of measuring optical resonator cavity in two laser wave strong points 1, τ 2, again according to formula
Figure BSA00000389457100072
With
Figure BSA00000389457100073
Calculate the reflectivity R of dual wavelength high reflection mirror 16 to be measured in two wavelength 1, R 2, L wherein 1For measuring optical resonator cavity chamber long.
In the chamber, extract two laser wave strong point ring-down times among the present invention the transmitted light and also can realize through optical spectroscopy, as shown in Figure 4.Two different wavelength of laser of output cavity mirror transmission are through beam splitter 17 (adopting grating or prism) beam split; Be focused lens 7-1 and condenser lens 7-2 then and focus on photodetector 8-1 and photodetector 8-2 respectively; After laser beam was turned off, photodetector 8-1 and photodetector 8-2 recorded signal respectively by single index attenuation function I (t)=Ae -t/ τ(A wherein, B is a constant coefficient to+B, in the multi-parameter fitting process, is made as free parameter, simulates the ring-down time τ of initial optical resonator cavity in two laser wave strong points 01, τ 02Equally, under measuring optical resonator cavity situation, the optical cavity ring-down signal that two photodetectors record is respectively by single index attenuation function I (t)=A 1e -t/ τ+ B 1, A wherein 1, B 1Be constant coefficient, in the multi-parameter fitting process, be made as free parameter, simulate the ring-down time τ of measuring optical resonator cavity in two laser wave strong points 1, τ 2, according to formula
Figure BSA00000389457100074
With
Figure BSA00000389457100075
L wherein 0For initial optical resonator cavity chamber long, L 1Long for measuring optical resonator cavity chamber, calculate the reflectivity R of dual wavelength high reflection mirror 16 to be measured in two wavelength 1, R 2
Be illustrated in figure 5 as and adopt mechanical shutter alternately to turn-off two laser, add mechanical shutter 18 at laser instrument light-emitting window front end, it is by computing machine 9 controls.Mechanical shutter 18 blocks a long wavelength laser output beam earlier under computing machine 9 controls in the process of measuring, and measures the initial optical resonator cavity and presses the single index attenuation function at the optical cavity ring-down signal of another wavelength
Figure BSA00000389457100076
(A wherein 01, B 01Be constant coefficient, in the multi-parameter fitting process, be made as free parameter, simulate ring-down time τ 01Block another wavelength laser bundle then, the optical cavity ring-down signal of the laser wave strong point that measurement initial optical resonator cavity formerly blocks is by the single index attenuation function
Figure BSA00000389457100077
(A wherein 02, B 02Be constant coefficient, in the multi-parameter fitting process, be made as free parameter, simulate ring-down time τ 02Equally, under measuring optical resonator cavity situation, earlier a long wavelength laser cuts out or this Laser Output Beam is blocked, measure the measuring optical resonator cavity and press the single index attenuation function at the optical cavity ring-down signal of another wavelength
Figure BSA00000389457100078
Simulate ring-down time τ 1, A wherein 11, B 11Be constant coefficient (in the multi-parameter fitting process, being made as free parameter); Close or block another wavelength laser bundle then, the optical cavity ring-down signal of the laser wave strong point that measurement measuring optical resonator cavity formerly is closed or blocks is by the single index attenuation function
Figure BSA00000389457100079
Simulate ring-down time τ 2, A wherein 12, B 12For constant coefficient (in the multi-parameter fitting process, being made as free parameter), again according to formula
Figure BSA00000389457100081
With
Figure BSA00000389457100082
Calculate the reflectivity R of dual wavelength high reflection mirror 16 to be measured in two wavelength 1, R 2, L wherein 1For measuring optical resonator cavity chamber long.
Initial optical resonator cavity among the present invention and measuring optical resonator cavity can adopt frequency selectivity light feedback light cavity configuration.Initial optical resonator cavity as shown in Figure 6 is made up of 5,6 and plane dual wavelength high reflection mirrors 19 of two identical plano-concave dual wavelength high reflection mirrors; Plane dual wavelength high reflection mirror 19 is for incident chamber mirror and favour the optical axis placement; Incoming laser beam impinges perpendicularly on the plano-concave dual wavelength high reflection mirror of placing perpendicular to optical axis 6 after dual wavelength high reflection mirror 19 transmissions of plane; Laser beam is back to plane dual wavelength high reflection mirror 19 by plano-concave dual wavelength high reflection mirror 6 reflection backs by former road; Again by 19 reflections of plane dual wavelength high reflection mirror, reflected light impinges perpendicularly on plano-concave dual wavelength high reflection mirror 5 then; Between the plano-concave dual wavelength high reflection mirror 5 of initial optical resonator cavity and plane dual wavelength high reflection mirror 19, insert dual wavelength high reflection mirror 16 to be measured; After incoming laser beam sees through plane dual wavelength high reflection mirror 19; After successively reflecting once more with plane dual wavelength high reflection mirror 19 through plano-concave dual wavelength high reflection mirror 6; Incide dual wavelength high reflection mirror 16 to be measured, incident angle is a dual wavelength high reflection mirror use angle to be measured, and the light that reflects from dual wavelength high reflection mirror 16 to be measured impinges perpendicularly on plano-concave dual wavelength high reflection mirror 5; So just constituted stable measuring optical resonator cavity, as shown in Figure 7.
In a word, the present invention proposes the measuring method of dual wavelength high reflection mirror reflectivity, its measurement result is the influence of Stimulated Light device strength fluctuation not, and can measure all kinds of dual wavelength high reflection mirror reflectivity from the ultraviolet to the mid and far infrared.This method can obtain the reflectivity of dual wavelength high reflection mirror in two wavelength, if increase quantity of light source, can obtain the reflectivity in a plurality of wavelength.The present invention has simple in structure, measuring accuracy height and low cost and other advantages.
The present invention does not set forth the known technology that part belongs to art technology in detail.

Claims (10)

1. dual wavelength high reflection mirror method for measuring reflectance is characterized in that performing step is following:
(1) continuous laser with two different wave lengths of light intensity periodic modulation incides the initial optical resonator cavity simultaneously;
Said initial optical resonator cavity is placed perpendicular to optical axis relatively by two identical plano-concave dual wavelength high reflection mirror concave surfaces and is formed, and incident light impinges perpendicularly on second plano-concave dual wavelength high reflection mirror after seeing through from first plano-concave dual wavelength high reflection mirror center;
Or the initial optical resonator cavity is made up of two identical plano-concave dual wavelength high reflection mirrors and a plane dual wavelength high reflection mirror; Plane dual wavelength high reflection mirror is incident chamber mirror and favours the optical axis placement; Incoming laser beam impinges perpendicularly on first plano-concave high reflection mirror placing perpendicular to optical axis after this plane high reflection mirror transmission; Laser beam is back to plane dual wavelength high reflection mirror by first plano-concave dual wavelength high reflection mirror reflection back by former road; Again by plane dual wavelength high reflection mirror secondary reflection again, reflected light impinges perpendicularly on second plano-concave dual wavelength high reflection mirror then;
(2) two different wavelength of laser from two plano-concave dual wavelength high reflection mirrors transmission of said initial optical resonator cavity focus on photodetector by condenser lens; Photodetector is surveyed the optical cavity ring-down signal of initial optical resonator cavity; When the optical cavity ring-down signal amplitude of initial optical resonator surpasses setting threshold; Trigger and turn-off incoming laser beam; Write down the optical cavity ring-down signal of initial optical resonator cavity, perhaps write down the optical cavity ring-down signal of initial optical resonator cavity, utilize simultaneous measurement method or divide optical probe method or replace mensuration to obtain the ring-down time τ of initial optical resonator cavity in two laser wave strong points at the negative edge of modulation signal 01, τ 02, and then obtain the average reflectance R of dual wavelength high reflective cavity mirror in two wavelength 01, R 02
(3) use angle according to dual wavelength high reflection mirror to be measured adds dual wavelength high reflection mirror to be measured in the initial optical resonator cavity, constitutes the measuring optical resonator cavity;
Constituting of said measuring optical resonator cavity: incident light first plano-concave dual wavelength high reflection mirror center from the initial optical resonator cavity gets into; Keep first plano-concave dual wavelength high reflection mirror position motionless; Between two plano-concave dual wavelength high reflection mirrors, add dual wavelength high reflection mirror to be measured; Laser beam incides dual wavelength high reflection mirror to be measured after seeing through first plano-concave dual wavelength high reflection mirror; Incident angle is a dual wavelength high reflection mirror use angle, and the position that changes second plano-concave dual wavelength high reflection mirror makes from dual wavelength high reflection mirror laser light reflected bundle to be measured and impinges perpendicularly on second plano-concave dual wavelength high reflection mirror, constitutes the measuring optical resonator cavity;
Or the constituting of measuring optical resonator cavity: plane dual wavelength high reflection mirror is incident chamber mirror and favours optical axis and place; Incoming laser beam impinges perpendicularly on first plano-concave dual wavelength high reflection mirror placing perpendicular to optical axis after this plane dual wavelength high reflection mirror transmission; Laser beam is back to plane dual wavelength high reflection mirror by first plano-concave dual wavelength high reflection mirror reflection back by original optical path; Again by plane dual wavelength high reflection mirror secondary reflection again, reflected light impinges perpendicularly on second plano-concave dual wavelength high reflection mirror then; Between second plano-concave dual wavelength high reflection mirror of initial optical resonator cavity and plane dual wavelength high reflection mirror, insert dual wavelength high reflection mirror to be measured; After incoming laser beam sees through plane dual wavelength high reflection mirror; Successively through behind first plano-concave dual wavelength high reflection mirror and the plane dual wavelength high reflection mirror; Incide dual wavelength high reflection mirror to be measured; Incident angle is a dual wavelength high reflection mirror use angle to be measured, impinges perpendicularly on second plano-concave dual wavelength high reflection mirror from dual wavelength high reflection mirror laser light reflected bundle to be measured, constitutes the measuring optical resonator cavity;
(4) two different wavelength of laser from the transmission of dual wavelength high reflective cavity mirror focus on photodetector by condenser lens; Photodetector is surveyed the optical cavity ring-down signal; When measuring optical resonator cavity output optical cavity ring-down signal amplitude surpasses setting threshold; Trigger and turn-off incoming laser beam; Write down the optical cavity ring-down signal of measuring optical resonator cavity, perhaps write down the optical cavity ring-down signal of measuring optical resonator cavity, utilize simultaneous measurement method or divide optical probe method or replace mensuration to obtain the ring-down time τ of measuring optical resonator cavity in two laser wave strong points at the negative edge of modulation signal 1, τ 2, through calculating the reflectivity R of dual wavelength high reflection mirror to be measured in two wavelength 1, R 2
Described simultaneous measurement method obtains the reflectivity R of dual wavelength high reflection mirror to be measured in two wavelength 1, R 2Implementation procedure following: the optical cavity ring-down signal of the initial optical resonator cavity of record in the step (2) press double-exponential function decays, Δ t is poor for the two laser turn-off time, A 01, A 02, A 03Be constant coefficient, utilize the match of multi-parameter fitting program to obtain the ring-down time τ of initial optical resonator cavity in two laser wave strong points 01, τ 02Equally, under measuring optical resonator cavity situation, the optical cavity ring-down signal of the measuring optical resonator cavity of record in the step (4) is pressed the double-exponential function decay, I ( t ) = A 11 e - t / τ 1 + A 22 e - ( t + Δ t ) / τ 2 + A 33 , A 11 , A 12 , A 13 Be constant coefficient, utilize the match of multi-parameter fitting program to obtain the ring-down time τ of measuring optical resonator cavity in two laser wave strong points 1, τ 2, according to formula With
Figure FSB00000706382200024
L wherein 0For initial optical resonator cavity chamber long, L 1Long for measuring optical resonator cavity chamber, calculate the reflectivity R of dual wavelength high reflection mirror to be measured in two wavelength 1, R 2
Optical probe method obtained the reflectivity R of dual wavelength high reflection mirror to be measured in two wavelength in said minute 1, R 2Implementation procedure following: with initial optical resonator cavity output signal in the step (2) through the beam splitter beam split; Two different wavelength of laser are focused on different photodetectors respectively, and the optical cavity ring-down signal that two photodetectors record is respectively by single index attenuation function I (t)=Ae -t/ τ+ B, A wherein, B is a constant coefficient, simulates the ring-down time τ of initial optical resonator cavity in two laser wave strong points 01, τ 02Equally; Under measuring optical resonator cavity situation; Measuring optical resonator cavity in the step (4) is exported signal through the beam splitter beam split, and two different wavelength of laser are focused on different photodetectors respectively, and the optical cavity ring-down signal that two photodetectors record is respectively by single index attenuation function I (t)=A 1e -t/ τ+ B 1, A wherein 1, B 1Be constant coefficient, simulate the ring-down time τ of measuring optical resonator cavity in two laser wave strong points 1, τ 2, according to formula
Figure FSB00000706382200025
With
Figure FSB00000706382200026
L wherein 0For initial optical resonator cavity chamber long, L 1Long for measuring optical resonator cavity chamber, calculate the reflectivity R of dual wavelength high reflection mirror to be measured in two wavelength 1, R 2
Said alternately mensuration obtains the reflectivity R of dual wavelength high reflection mirror to be measured in two wavelength 1, R 2Implementation procedure following: adopt mechanical shutter or electric switch method alternately to close two laser; In the process of measuring, earlier a long wavelength laser cuts out or this Laser Output Beam is blocked, the initial optical resonator cavity of record in the step (2) is pressed the single index attenuation function at the optical cavity ring-down signal of another wavelength
Figure FSB00000706382200027
Simulate ring-down time τ 01, A wherein 01, B 01Be constant coefficient; Close or block another wavelength laser bundle then, the optical cavity ring-down signal of the laser wave strong point that the initial optical resonator cavity of record in the step (2) formerly is closed or blocks is by the single index attenuation function
Figure FSB00000706382200031
Simulate ring-down time τ 02, A wherein 02, B 02Be constant coefficient; Equally, under measuring optical resonator cavity situation, earlier a long wavelength laser cuts out or this Laser Output Beam is blocked, the measuring optical resonator cavity of record in the step (4) is pressed the single index attenuation function at the optical cavity ring-down signal of another wavelength
Figure FSB00000706382200032
Simulate ring-down time τ 1, A wherein 11, B 11Be constant coefficient; Close or block another wavelength laser bundle then, the optical cavity ring-down signal of the laser wave strong point that the measuring optical resonator cavity of record in the step (4) formerly is closed or blocks is by the single index attenuation function
Figure FSB00000706382200033
Simulate ring-down time τ 2, A wherein 12, B 12Be constant coefficient, according to formula With L wherein 0For initial optical resonator cavity chamber long, L 1Long for measuring optical resonator cavity chamber, calculate the reflectivity R of dual wavelength high reflection mirror to be measured in two wavelength 1, R 2
2. dual wavelength high reflection mirror method for measuring reflectance according to claim 1 is characterized in that: described two continuous lasers are by semiconductor laser or solid state laser or gas laser generation.
3. dual wavelength high reflection mirror method for measuring reflectance according to claim 1 is characterized in that: the reflectivity of the plano-concave dual wavelength high reflection mirror of described initial optical resonator cavity and measuring optical resonator cavity and plane dual wavelength high reflection mirror in two wavelength all greater than 99%.
4. dual wavelength high reflection mirror method for measuring reflectance according to claim 1; It is characterized in that: described initial optical resonator cavity and measuring optical resonator cavity are stable cavity or confocal resonator; Total long L in chamber satisfies 0＜L≤2r, and wherein r is the radius-of-curvature of plano-concave dual wavelength high reflection mirror concave surface.
5. dual wavelength high reflection mirror method for measuring reflectance according to claim 1 is characterized in that: trigger in said step (2) and (4) and turn-off two incoming laser beams and realize one of in the following manner:
When a. adopting the continuous semiconductor laser instrument, when initial optical resonator or measuring optical resonator cavity output signal amplitude is higher than setting threshold, quick closedown semiconductor laser exciting current or voltage;
When b. adopting continuous semiconductor laser instrument or solid state laser or gas laser; When initial optical resonator or measuring optical resonator cavity output signal amplitude is higher than setting threshold, between laser instrument and dual wavelength high reflective cavity mirror, adopt fast optical switch based to close laser beam;
C. adopt the square-wave frequency modulation fast optical switch based, or during square-wave frequency modulation laser instrument excitation power supply, when initial optical resonator or measuring optical resonator cavity output signal amplitude are higher than setting threshold, utilize the square wave negative edge to close laser beam.
6. dual wavelength high reflection mirror method for measuring reflectance according to claim 1 is characterized in that: the optical cavity ring-down signal of the initial optical resonator cavity in the said step (2) is by oscillograph or data collecting card record.
7. dual wavelength high reflection mirror method for measuring reflectance according to claim 5 is characterized in that: described fast optical switch based is electrooptical modulation switch or acoustooptic modulation switch.
8. dual wavelength high reflection mirror method for measuring reflectance according to claim 1 is characterized in that: described beam splitter is grating or prism.
9. dual wavelength high reflection mirror method for measuring reflectance according to claim 1 is characterized in that: described method for measuring reflectance is used for three-wavelength or multi-wavelength high reflection mirror albedo measurement more.
10. dual wavelength high reflection mirror method for measuring reflectance according to claim 1 is characterized in that: said photodetector is a plurality of single-element detectors, or the high-speed photodetector of a linear array.
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