CN100559146C - A kind of method of determining high reflective cavity mirror and test mirrors reflectivity simultaneously - Google Patents

Abstract

A kind of method of determining high reflective cavity mirror and test mirrors reflectivity simultaneously, it is characterized in that: the continuous laser of intensity modulated incides the stable resonator that two plano-concave high reflective cavity mirrors are formed, measure the amplitude and the phase place of optical cavity output signal first harmonic with phase-lock mode, holding chamber is long constant, add high reflection measurement mirror and constitute folded cavity, repeat said process, measure the folded cavity amplitude and the phase place of respective frequencies, and then obtain the quotient of amplitudes and the phase difference value of two kinds of chamber type respective frequencies.Calculated in the value of two Frequency points with the change curve match of modulating frequency or by both by both, obtain cavity mirrors reflectivity and test mirrors reflectivity simultaneously, the present invention has efficiency of measurement and the high advantage of measuring accuracy.

Description

A kind of method of determining high reflective cavity mirror and test mirrors reflectivity simultaneously

Technical field

The present invention relates to a kind of measuring method, a kind of especially method of determining chamber mirror and test mirrors reflectivity simultaneously to optical component parameter.

Background technology

High reflectance is accurately measured in the widely-used an urgent demand of high reflectance optical element in laser system, and classic method can't satisfy the measuring accuracy requirement of high reflectance as spectrophotometer." a kind of measuring method of high specular reflectivity of reflector ", Chinese patent application numbers 98114152.8, publication number CN1242516A, open January 26 2000 date and " compound declining swung the accurate measure CO IL of optical cavity technology chamber mirror high reflectance ", the light laser and the particle beams, Sheng Xinzhi, Sun Fuge etc., the 10th volume the 2nd phase 199-202 page or leaf, a kind of high reflectivity measurement method is provided in May, 1998, this method adopts pulse laser to make light source, in the optical cavity ring-down mode of folded cavity and straight chamber combination, has reduced because intracavity gas absorbs, the measuring error that scattering and diffraction equal loss cause, but the measuring accuracy of this method is subjected to pulsed laser beam of poor quality, the restriction of factors such as laser cavity internal schema competition, and because the pulse laser system of using, the cost height is not easy to promote the use of." a kind of measuring method of reflectance ratio of high reflected mirror ", Chinese patent application numbers 200610011254.9, publication number CN1804572A, open July 19 2006 date and " continuous laser optical cavity ring-down method is accurately measured high reflectance ", Chinese laser, Gong Yuan, Li Bincheng, the 33rd volume the 9th phase 1247-1250 page or leaf, a kind of high reflectivity measurement method of making light source with wide range continuous semiconductor laser instrument has been proposed in September, 2006, this method is by the output intensity of function generator square-wave frequency modulation semiconductor laser, laser is repeatedly reflection in the stable resonator that two high reflective cavity mirrors are formed, the amplitude of optical cavity output signal first harmonic and phase place (hereinafter to be referred as " amplitude and phase place ") are recorded by lock-in amplifier, obtain cavity mirrors reflectivity by amplitude and phase place with the change curve match of modulating frequency then.The factors such as finite bandwidth of finite response time, detector and the lock-in amplifier of laser instrument (being system frequency response or system responses) can cause that measurement result is inaccurate in the measuring process, so this method must be eliminated the influence of system responses.The concrete steps that cavity mirrors reflectivity is measured in straight chamber are: (1) measures straight chamber signal.Constitute straight chamber by two chamber mirrors, change modulating frequency in a certain scope, write down a series of amplitudes and phase value by lock-in amplifier, promptly amplitude and phase place are with the change curve of modulating frequency; (2) measuring system response.Remove a chamber mirror, amplitude and phase value when writing down identical modulating frequency; (3) influence of elimination system responses.During the corresponding modulating frequency, straight chamber amplitude is divided by the system responses amplitude, and straight chamber phase place deducts the system responses phase place; (4) obtain cavity mirrors reflectivity by the straight chamber amplitude of having eliminated system responses and phase place with the change curve match of modulating frequency.When the reflectivity of chamber mirror and test mirrors all needed to determine, step was as follows: at first measure straight chamber signal and system responses, adopt said method to determine cavity mirrors reflectivity; Insert test mirrors and constitute folded cavity, amplitude and phase place are with the change curve of modulating frequency when measuring folded cavity; Repeat the system frequency response in above-mentioned steps (3) the elimination folded cavity signal; Then with cavity mirrors reflectivity as known parameters, obtain the test mirrors reflectivity by the folded cavity amplitude of having eliminated system responses and phase place with the change curve match of modulating frequency.Because must measure and the elimination system responses, the efficiency of measurement of this method and precision have been subjected to certain restriction.

Summary of the invention

Technology of the present invention is dealt with problems: overcome the deficiencies in the prior art, provide a kind of efficiency of measurement the high and high method that can determine high reflective cavity mirror and test mirrors reflectivity simultaneously of measuring accuracy.

Technical solution of the present invention: a kind of method of determining high reflective cavity mirror and test mirrors reflectivity simultaneously, its characteristics are to realize by following steps:

(1) with the continuous laser of square wave or sine wave modulation, incide stable resonator or confocal resonator that two identical plano-concave high reflective cavity mirrors are formed, survey the amplitude A of straight chamber output signal first harmonic ₁(f) and phase ₁(f);

(2) holding chamber is long constant, adds high reflection measurement mirror and constitute folded cavity between two identical plano-concave high reflective cavity mirrors, measures the amplitude A under the folded cavity respective frequencies ₂(f) and phase ₂(f);

(3) be divided by by the amplitude of straight chamber and two kinds of chambeies of folded cavity type respective frequencies and phase place is subtracted each other and obtained quotient of amplitudes R respectively _A(f) and phase difference value Δ φ (f);

(4) by the quotient of amplitudes R of two kinds of chamber type corresponding modulating frequencies _A(f) and phase difference value Δ φ (f), determine straight chamber ring-down time τ by the frequency curve match ₁With folded cavity ring-down time τ ₂, calculate cavity mirrors reflectivity R and test mirrors reflectivity R _x, perhaps by the quotient of amplitudes R of two kinds of chamber type corresponding modulating frequencies _A(f) and phase difference value Δ φ (f), determine cavity mirrors reflectivity R and test mirrors reflectivity R by direct calculating _x

The present invention compared with prior art has following advantage:

(1) high-level efficiency.Owing to need not the measuring system response, reduced measuring process, can determine cavity mirrors reflectivity and test mirrors reflectivity simultaneously, improved efficient.

(2) high precision.In the measuring system response process, can introduce error, reduce measuring accuracy to a certain extent.The present invention has improved the late time data disposal route, thereby need not the measuring system response, has further improved measuring accuracy.

Description of drawings

Fig. 1 is a straight chamber of the present invention measurement mechanism synoptic diagram;

Fig. 2 is a folded cavity structural representation of the present invention.

Embodiment

As shown in Figure 1, measurement mechanism of the present invention is made up of function generator 1, light source 2, spatial filtering and telescopic system 3, plano-concave high reflective mirror 4,5, convergent lens 6, detector 7 and lock-in amplifier 8.Thick line is represented light path, and fine rule represents that signal wire links to each other.Function generator 1 has two outputs, and an output is connected to light source 2 makes laser instrument output intensity square-wave frequency modulation, and another output is connected to lock-in amplifier 8 conducts with reference to signal.Can be by the frequency shift square-wave modulation signal frequency of adjustment function generator.Light source 2 adopts the semiconductor laser that can modulate.Spatial filtering and telescopic system 3 are made up of two lens and a pin hole, with incoming laser beam be shaped to basic mode and with the optical cavity pattern match.Two identical plano- concave mirrors 4,5, concave surface plating high-reflecting film (reflectivity is greater than 99%), concave surface constitutes straight chamber relatively.Continuous laser beam is repeatedly reflection back output in resonator cavity, assembles through lens 6, is received by detector 7 again.Detector 7 converts light signal to electric signal, outputs to lock-in amplifier 8 signal input parts then, with the amplitude and the phase place of record periodic electrical signal first harmonic.As shown in Figure 2, adding high reflection measurement mirror 9 backs and constitute folded cavitys, can measure the reflectivity of any reflectivity greater than 99% plane high reflective mirror, is the 1-85 degree to high reflection measurement mirror angle to be measured.Minimum test angle is by the long ratio decision in chamber mirror diameter and chamber among the present invention, for example when the used about 30mm of chamber mirror diameter and chamber are about 2m, can measure the reflectivity of 1 high reflection measurement mirror when spending incident, and the full test angle can be spent near 90.Continuous laser adopts the solid state laser or the gas laser of continuous semiconductor laser instrument or diode pumping, the continuous laser of square wave or sine wave modulation is by the drive current of semiconductor laser modulation or voltage, perhaps adopts acousto-optic modulator, electrooptic modulator, chopper modulation continuous laser beam to realize.The modulating frequency variation range is 10Hz～2MHz.

Have dual mode to determine the reflectivity of high reflective cavity mirror and test mirrors simultaneously:

Mode one: frequency curve match.At first, measure the amplitude of straight chamber output signal first harmonic and phase place change curve with modulating frequency

$A_1\left(f\right)=a_1\sqrt{\frac{1}{1+{\left(2\mathrm{\π}{\mathrm{f\τ}}_1\right)}^2}},---\left(1\right)$

φ ₁(f)＝-atan(2πfτ ₁) (2)

Insert test mirrors 9 then and constitute folded cavity, amplitude and phase place when measuring folded cavity under the respective frequencies

$A_2\left(f\right)=a_2\sqrt{\frac{1}{1+{\left(2\mathrm{\π}{\mathrm{f\τ}}_2\right)}^2}},---\left(3\right)$

φ ₂(f)＝-atan(2πfτ ₂). (4)

The amplitude of two kinds of chamber type respective frequencies is divided by and obtains quotient of amplitudes

$R_A\left(f\right)=\frac{A_2\left(f\right)}{A_1\left(f\right)}=a\sqrt{\frac{1+{\left(2\mathrm{\π}{\mathrm{f\τ}}_1\right)}^2}{1+{\left(2\mathrm{\π}{\mathrm{f\τ}}_2\right)}^2}},---\left(5\right)$

Quotient of amplitudes with the variation tendency of modulating frequency as shown in Figure 3, factor a=1 wherein, promptly amplitude is by low frequency value normalization.The phase place of two kinds of chamber type respective frequencies is subtracted each other and is obtained phase difference value

Δφ(f)＝φ ₂(f)-φ ₁(f)＝atan(2πfτ ₁)-atan(2πfτ ₂)，(6)

Phase difference value with the variation tendency of modulating frequency as shown in Figure 4.After obtaining quotient of amplitudes and phase difference value delta data, have three kinds of match modes can both obtain cavity mirrors reflectivity and test mirrors reflectivity with modulating frequency:

A. by quotient of amplitudes R _A(f) the change curve match with modulating frequency obtains straight chamber ring-down time τ ₁With folded cavity ring-down time τ ₂, again by

${\mathrm{\τ}}_1=-\frac{L}{c\ln R},---\left(7\right)$

${\mathrm{\τ}}_2=-\frac{L}{c\ln \left({\mathrm{RR}}_x\right)},---\left(8\right)$

Calculate cavity mirrors reflectivity R and test mirrors reflectivity R _x, L is chamber long (needing to measure), c is the light velocity (known constant).Perhaps with (7) (8) formula substitutions (5) (6) formula, by quotient of amplitudes R _A(f) the change curve match with modulating frequency directly obtains cavity mirrors reflectivity R and test mirrors reflectivity R _xBelow all direct matches or calculate cavity mirrors reflectivity R and test mirrors reflectivity R _xMode, all can first match or calculate straight chamber ring-down time τ ₁With folded cavity ring-down time τ ₂, calculate reflectivity by ring-down time again.For simplicity, only mention the former below.

B. obtain cavity mirrors reflectivity R and test mirrors reflectivity R by phase difference value Δ φ (f) with the change curve match of modulating frequency _x

C. by quotient of amplitudes R _A(f) and phase difference value Δ φ (f) obtain cavity mirrors reflectivity R and test mirrors reflectivity R with the change curve match of modulating frequency _x

Mode two: directly calculate.At first, measure and calculate R by mode one described step _A(f) and Δ φ (f) in the value of two Frequency points, set up about τ ₁, τ ₂(or R, R _x) system of equations, calculate cavity mirrors reflectivity R and test mirrors reflectivity R again _xTwo kinds of approach are specifically arranged:

A. by the value of Δ φ (f) at two Frequency points

$\left\{\begin{array}{c}\mathrm{\&Delta;\&phi;}\left(f_1\right)=a\tan \left(2\mathrm{\&pi;}{\mathrm{<figure-callout\; id="1"\; label="f"\; filenames="C20061011436300111.png"\; state="\{\{state\}\}">f</figure-callout>}}_1{\mathrm{\&tau;}}_1\right)-a\tan \left(2\mathrm{\&pi;}{\mathrm{<figure-callout\; id="1"\; label="f"\; filenames="C20061011436300111.png"\; state="\{\{state\}\}">f</figure-callout>}}_1{\mathrm{\&tau;}}_2\right)\\ \mathrm{\&Delta;\&phi;}\left(f_2\right)=a\tan \left(2\mathrm{\&pi;}{\mathrm{<figure-callout\; id="2"\; label="f"\; filenames="C20061011436300111.png"\; state="\{\{state\}\}">f</figure-callout>}}_2{\mathrm{\&tau;}}_1\right)-a\tan \left(2\mathrm{\&pi;}{\mathrm{<figure-callout\; id="2"\; label="f"\; filenames="C20061011436300111.png"\; state="\{\{state\}\}">f</figure-callout>}}_2{\mathrm{\&tau;}}_2\right)\end{array}\right.---\left(9\right)$

Calculate straight chamber ring-down time τ ₁With folded cavity ring-down time τ ₂, calculate cavity mirrors reflectivity R and test mirrors reflectivity R by (7) (8) formula again _xPerhaps, directly calculate cavity mirrors reflectivity R and test mirrors reflectivity R with (7) (8) formula substitutions (9) formula _xWherein a kind of special circumstances are (2n+1) f ₂=(2m+1) f ₁, m, n are nonnegative integer and m ≠ n.In this case, need not to change the modulating frequency of function generator, only need phase place, can calculate cavity mirrors reflectivity and test mirrors reflectivity by lock-in amplifier record optical cavity output signal 2n+1 time and 2m+1 subharmonic.

B. by quotient of amplitudes R _A(f) at two Frequency point f ₁, f ₂Value and phase difference value Δ φ (f) Frequency point f therein ₁Or f ₂(get f herein ₁) value

$\left\{\begin{array}{c}{R}_A\left(f_1\right)=a\sqrt{\frac{1+{\left(2\mathrm{\&pi;}{\mathrm{<figure-callout\; id="1"\; label="f"\; filenames="C20061011436300111.png"\; state="\{\{state\}\}">f</figure-callout>}}_1{\mathrm{\&tau;}}_1\right)}^2}{1+{\left(2\mathrm{\&pi;}{\mathrm{<figure-callout\; id="1"\; label="f"\; filenames="C20061011436300111.png"\; state="\{\{state\}\}">f</figure-callout>}}_1{\mathrm{\&tau;}}_2\right)}^2}}\\ \mathrm{\&Delta;\&phi;}\left(f_1\right)=a\tan \left(2\mathrm{\&pi;}{\mathrm{<figure-callout\; id="1"\; label="f"\; filenames="C20061011436300111.png"\; state="\{\{state\}\}">f</figure-callout>}}_1{\mathrm{\&tau;}}_1\right)-a\tan \left(2\mathrm{\&pi;}{\mathrm{<figure-callout\; id="1"\; label="f"\; filenames="C20061011436300111.png"\; state="\{\{state\}\}">f</figure-callout>}}_1{\mathrm{\&tau;}}_2\right)\\ R_A\left(f_2\right)=a\sqrt{\frac{1+{\left(2\mathrm{\&pi;}{\mathrm{<figure-callout\; id="2"\; label="f"\; filenames="C20061011436300111.png"\; state="\{\{state\}\}">f</figure-callout>}}_2{\mathrm{\&tau;}}_1\right)}^2}{1+{\left(2\mathrm{\&pi;}{\mathrm{<figure-callout\; id="2"\; label="f"\; filenames="C20061011436300111.png"\; state="\{\{state\}\}">f</figure-callout>}}_2{\mathrm{\&tau;}}_2\right)}^2}}\end{array}\right.---\left(10\right)$

Calculate straight chamber ring-down time τ ₁, folded cavity ring-down time τ ₂And amplitude factor a, calculate cavity mirrors reflectivity R and test mirrors reflectivity R by (7) (8) formula again _xPerhaps, directly calculate cavity mirrors reflectivity R, test mirrors reflectivity R with (7) (8) formula substitutions (10) formula _xAnd amplitude factor a.Equally as previously mentioned, f ₁, f ₂Can select the different odd subfrequency of same modulating frequency.

Claims (12)

1, a kind of method of determining high reflective cavity mirror and test mirrors reflectivity simultaneously is characterized in that realizing by following steps:

(1) with the continuous laser of square wave or sine wave modulation, incide stable resonator or confocal resonator that two identical plano-concave high reflective cavity mirrors are formed, survey the amplitude A of straight chamber output signal first-harmonic ₁(f) and phase ₁(f);

(2) holding chamber is long constant, adds high reflection measurement mirror and constitute folded cavity between two identical plano-concave high reflective cavity mirrors, measures the amplitude A under the folded cavity corresponding modulating frequency ₂(f) and phase ₂(f);

(3) be divided by by the amplitude of straight chamber and two kinds of chambeies of folded cavity type corresponding modulating frequency and phase place is subtracted each other and obtained quotient of amplitudes R respectively _A(f) and phase difference value Δ φ (f);

(4) by the quotient of amplitudes R of two kinds of chamber type corresponding modulating frequencies _A(f) and phase difference value Δ φ (f), determine straight chamber ring-down time τ by the frequency curve match ₁With folded cavity ring-down time τ ₂, calculate cavity mirrors reflectivity R and test mirrors reflectivity R _x, perhaps by the quotient of amplitudes R of two kinds of chamber type corresponding modulating frequencies _A(f) and phase difference value Δ φ (f), determine cavity mirrors reflectivity R and test mirrors reflectivity R by direct calculating _x

2, the method for determining high reflective cavity mirror and test mirrors reflectivity simultaneously according to claim 1, it is characterized in that: the continuous laser in the described step (1) adopts the continuous solid body laser instrument of continuous semiconductor laser instrument, continuous wave gas laser or diode pumping.

3, the method for determining high reflective cavity mirror and test mirrors reflectivity simultaneously according to claim 1, it is characterized in that: the square wave in the described step (1) or the continuous laser of sine wave modulation are drive current or the voltage by semiconductor laser modulation, perhaps adopt acousto-optic modulator, electrooptic modulator, chopper modulation continuous laser beam to realize.

4, the method for determining high reflective cavity mirror and test mirrors reflectivity simultaneously according to claim 1, it is characterized in that: the modulating frequency variation range of described step (1) is 10Hz～2MHz.

5, the method for determining high reflective cavity mirror and test mirrors reflectivity simultaneously according to claim 1, it is characterized in that: described step (4) medium frequency curve-fitting method is: adopt quotient of amplitudes R _A(f) with the change curve match of modulating frequency, determine straight chamber ring-down time τ simultaneously ₁With folded cavity ring-down time τ ₂

6, the method for determining high reflective cavity mirror and test mirrors reflectivity simultaneously according to claim 1, it is characterized in that: described step (4) medium frequency curve-fitting method is: adopt the change curve match of phase difference value Δ φ (f) with modulating frequency, determine straight chamber ring-down time τ simultaneously ₁With folded cavity ring-down time τ ₂

7, the method for determining high reflective cavity mirror and test mirrors reflectivity simultaneously according to claim 1, it is characterized in that: described step (4) medium frequency curve-fitting method is: quotient of amplitudes R _A(f) and phase difference value Δ φ (f) with the change curve match of modulating frequency, determine straight chamber ring-down time τ simultaneously ₁With folded cavity ring-down time τ ₂

8, the method for determining high reflective cavity mirror and test mirrors reflectivity simultaneously according to claim 1, it is characterized in that: direct calculation method is in the described step (4): according to phase difference value Δ φ (f) at any two Frequency point f ₁, f ₂, wherein comprise (2n+1) f ₂=(2m+1) f ₁, m, n is the value of nonnegative integer and m ≠ n, establishes an equation directly to calculate, and determines straight chamber ring-down time τ simultaneously ₁With folded cavity ring-down time τ ₂, calculate cavity mirrors reflectivity R and test mirrors reflectivity R again _x, perhaps according to phase difference value Δ φ (f) at any two Frequency point f ₁, f ₂, wherein comprise (2n+1) f ₂=(2m+1) f ₁, m, n are the value of nonnegative integer and m ≠ n, directly calculate cavity mirrors reflectivity R and test mirrors reflectivity R _x

9, the method for determining high reflective cavity mirror and test mirrors reflectivity simultaneously according to claim 1, it is characterized in that: direct calculation method is in the described step (4): according to quotient of amplitudes R _A(f) at two Frequency point f ₁, f ₂Value and phase difference value Δ φ (f) value of a Frequency point therein, establish an equation and directly calculate, determine straight chamber ring-down time τ simultaneously ₁With folded cavity ring-down time τ ₂, calculate cavity mirrors reflectivity R and test mirrors reflectivity R again _x, perhaps according to quotient of amplitudes R _A(f) at two Frequency point f ₁, f ₂Value and phase difference value Δ φ (f) value of a Frequency point therein, directly calculate cavity mirrors reflectivity R and test mirrors reflectivity R _x

10, the method for determining high reflective cavity mirror and test mirrors reflectivity simultaneously according to claim 1 is characterized in that: the high reflection measurement mirror test incident angle in the described step (2) is the 1-85 degree.

11, the method for determining high reflective cavity mirror and test mirrors reflectivity simultaneously according to claim 1 is characterized in that: two identical plano-concave high reflective cavity mirrors in the described step (1), and concave surface plating high-reflecting film, and concave surface constitutes straight chamber relatively.

12, the method for determining high reflective cavity mirror and test mirrors reflectivity simultaneously according to claim 1 is characterized in that: amplitude and the phase place of surveying straight chamber and folded cavity in described step (1) and the step (2) by lock-in amplifier.

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