CN101126676B - Laser beam switching timing optimization method for high reflection rate measurement - Google Patents

Abstract

The utility model discloses a method optimizing the sequence of opening and closing laser beam in measuring high reflectivity, belonging to the technical filed of measuring the parameters of optical elements. The optimization of the sequence of opening and closing the laser beam is achieved in two ways: squared modulation frequency and duty ratio are optimized so as to maximize the average amplitude of the optical cavity output signal of square wave trailing edge; when the amplitude of the optical cavity output signal is larger than the set threshold value, the threshold value triggers circuitto shut off the laser beam and the rising edge of next square wave cycle reopens the laser beam. The utility model has an advantage of improving the signal-to-noise ratio of decaying signal by optimi zing the sequence of opening and closing the laser beam so as to improve the precision of measuring the reflectivity.

Description

The timing optimization method that is used for the laser beam switching of high reflection rate measurement

Technical field

The present invention relates to a kind of method of measuring optical component parameter, relate to a kind of timing optimization method that is used for the laser beam switching of high reflection rate measurement especially.

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.Chinese patent application numbers 98114152.8, publication number CN1242516A, the patent of invention in open January 26 2000 date discloses " a kind of measuring method of high specular reflectivity of reflector ", adopt pulse laser system to make light source, incide the optical resonator that two high reflective mirrors are formed, receive the optical cavity index and decline and swing signal, determine respectively straight chamber ring-down time τ-and folded cavity ring-down time τ＜, calculate the reflectivity R of mirror to be measured.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 restricted; And, because employed pulse laser system cost height is unfavorable for promoting the use of.Chinese patent application numbers 200610011254.9, publication number CN1804572A, open 2006 date purpose application for a patent for invention in July 19 provides " a kind of measuring method of reflectance ratio of high reflected mirror "; " Chinese laser " that publish in September, 2006, Gong Yuan, Li Bincheng, the 33rd volume the 9th phase 1247-1250 page or leaf, disclose the method for a kind of " continuous laser optical cavity ring-down method is accurately measured high reflectance ", they have all proposed a kind ofly to make the high reflectivity measurement method of light source with the continuous semiconductor laser instrument, use the square-wave frequency modulation continuous laser, the amplitude that adopts phase-lock mode to survey output signal declines and swings and phase delay, thereby obtains optical cavity ring-down time and reflectance ratio of high reflected mirror.Swing the coupling efficiency in chamber to declining not high for laser power in this method.Chinese patent application numbers 200610165082.0, publication number CN1963435A, the patent of invention disclosed " method for measuring reflectance ratio of high reflected mirror " in open May 16 2007 date and the application for a patent for invention " high reflectivity measurement method of based semiconductor laser instrument self-mixing effect " of Chinese patent application 200710098755.X are controlled from first chamber mirror reflection by simple mechanical device or optical component and are returned the back to the feedback light light intensity of laser instrument, semiconductor laser output spectrum characteristic is changed, increase substantially laser beam and be coupled into to decline and swing the efficient of optical cavity, make to occur the very big spiking of amplitude in the optical cavity output signal.This spiking is used for obtaining index and declines and swing signal, and match obtains the reflectivity of chamber mirror and test mirrors.This method energy high-acruracy survey high reflectance, and cost is low, the device simple.Yet though the position that spike occurs in one-period is relatively stable, the particular location that occurs has certain random character, and amplitude fluctuation is bigger, signal to noise ratio (S/N ratio) and the reduction of high reflection rate measurement precision that making declines swings signal.

Summary of the invention

The technical problem to be solved in the present invention: overcome the deficiencies in the prior art, a kind of timing optimization method that is used for the laser beam switching of high reflection rate measurement is provided, this method is used for determining the highest moment of the maximum sharpness frequency of occurrences, turn-off laser beam constantly and write down the exponential damping signal at this, swing the signal to noise ratio (S/N ratio) of signal thereby improving declines, and further improve the high reflection rate measurement precision.

Technology of the present invention is dealt with problems: be used for the timing optimization method of the laser beam switching of high reflection rate measurement, it is characterized in that being realized by one of following scheme:

(1) with function generator or function square-wave frequency modulation semiconductor laser exciting current or the voltage that card is exported takes place, semiconductor laser is opened or turn-offed to square wave rising edge and negative edge correspondence respectively.Determine the moment of optical cavity output signal peak swing appearance and the time interval between the square wave rising edge

On this basis, optimize square-wave frequency modulation frequency f and/or dutycycle P and make optical cavity output signal peak swing be in the square wave negative edge, thereby turn-off laser beam, while triggering collection exponential damping signal, elapsed time Δ t ₂After, open laser beam again by the square wave rising edge of next cycle, repeat said process and realize declining swinging the duplicate measurements of signal and high reflectance.

(2) by the square-wave frequency modulation laser beam of threshold triggers circuit output, the rising edge of square wave and negative edge are corresponding respectively to be opened or the shutoff laser beam.When optical cavity output amplitude during greater than pre-set threshold, the threshold triggers circuit turn-offs its output current fast and forms negative edge and turn-off laser beam, triggering collection exponential damping signal simultaneously, elapsed time Δ t ₃After, open laser beam again by the square wave rising edge of next cycle, repeat said process and realize declining swinging the duplicate measurements of signal and high reflectance;

Described scheme (1) and scheme (2) are by one of following approach laser beam switching:

(1) realizes opening or turn-offing laser beam with the exciting current or the voltage of square-wave frequency modulation semiconductor laser;

(2) laser instrument itself is not modulated, and laser beam is exported continuously, at laser instrument and decline to swing between the chamber and insert electric light or acoustooptic switch, realizes opening or turn-offing laser beam with the exciting current or the voltage of square-wave frequency modulation photoswitch.

The initial value scope of square wave modulating frequency f is 1Hz～1MHz before optimizing in described scheme (1) and the scheme (2).

The initial value scope of dutycycle P is 10000: 1～1: 100 before optimizing in described scheme (1) and the scheme (2).

In the described scheme (1)

Be a plurality of Δ t ₁Assembly average, Δ t ₁The moment that peak swing occurs in the expression one-period and the time interval between this cycle square wave rising edge.

Described scheme (1) has following three kinds of forms to realize the optimization of modulating frequency and dutycycle by the timing optimization that control modulating frequency f and/or dutycycle P realize laser beam switching:

(1) modulating frequency f remains unchanged, and dutycycle P becomes $p=\stackrel{\&OverBar;}{\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="S2007101224086E00011.png,S2007101224086E00031.png"\; state="\{\{state\}\}">t</figure-callout>}}_1}/\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="S2007101224086E00011.png,S2007101224086E00021.png"\; state="\{\{state\}\}">t</figure-callout>}}_2,$ Wherein $\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="S2007101224086E00011.png,S2007101224086E00021.png"\; state="\{\{state\}\}">t</figure-callout>}}_2=T-\stackrel{\&OverBar;}{\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="S2007101224086E00011.png,S2007101224086E00031.png"\; state="\{\{state\}\}">t</figure-callout>}}_1},$ T＝1/f；

(2) modulating frequency f becomes $f=P/\left[(1+P)\stackrel{\&OverBar;}{\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="S2007101224086E00011.png,S2007101224086E00031.png"\; state="\{\{state\}\}">t</figure-callout>}}_1}\right],$ Dutycycle P remains unchanged, and wherein the initial value of dutycycle satisfies $\stackrel{\&OverBar;}{\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="S2007101224086E00011.png,S2007101224086E00031.png"\; state="\{\{state\}\}">t</figure-callout>}}_1}/10000\mathrm{\&tau;}<P<\stackrel{\&OverBar;}{\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="S2007101224086E00011.png,S2007101224086E00031.png"\; state="\{\{state\}\}">t</figure-callout>}}_1}/5\mathrm{\&tau;};$

(3) modulating frequency f becomes $f=1/(\stackrel{\&OverBar;}{\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="S2007101224086E00011.png,S2007101224086E00031.png"\; state="\{\{state\}\}">t</figure-callout>}}_1}+\mathrm{\&Delta;}{t}_2),$ Dutycycle P becomes $P=\stackrel{\&OverBar;}{\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="S2007101224086E00011.png,S2007101224086E00031.png"\; state="\{\{state\}\}">t</figure-callout>}}_1}/\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="S2007101224086E00011.png,S2007101224086E00021.png"\; state="\{\{state\}\}">t</figure-callout>}}_2,$ Δ t wherein ₂Be the integral multiple of ring-down time τ, i.e. Δ t ₂=k τ, τ does not swing signal and determines that roughly the k value is determined on a case-by-case basis by carrying out declining of timing optimization, and scope is 5＜k＜10000.

Threshold value in the described scheme (2) is set by the threshold triggers circuit, adjustable between 5mV～5V, initial value is an optical cavity output signal peak-peak, can not trigger within a certain period of time as if the threshold value that is provided with and turn-off then automatic small size the downward modulation till triggering of threshold value of laser beam.

Square wave in the described scheme (2) is generated by threshold triggers circuit itself or takes place to input to the threshold triggers circuit after card generates and by exporting after the threshold triggers circuit conversion by function generator or function.

Δ t in the described scheme (2) ₃Determine by following dual mode:

(1) the square-wave frequency modulation frequency remains unchanged, the Δ t in each cycle ₃The time interval that is carved into when triggering between the rising edge of next square-wave cycle is determined Δ t ₃Turn-off laser beam Δ t constantly because of triggering ₁Change and passive change, i.e. Δ t ₃=1/f-Δ t ₁

(2) Δ t ₃Remain unchanged, value is the integral multiple of ring-down time τ, i.e. Δ t ₃=k τ, τ does not swing signal and determines that roughly the k value is determined on a case-by-case basis by carrying out declining of timing optimization, and scope is 5＜k＜10000.This moment, the square-wave frequency modulation frequency was turn-offed laser beam Δ t constantly because of triggering ₁Change and passive change, i.e. f=1/ (Δ t ₃+ Δ t ₁).

The present invention compared with prior art has following advantage:

(1) turn-off laser beam and write down the exponential damping signal in the highest moment of the optical cavity output signal maximum sharpness frequency of occurrences, having improved declines swings Signal-to-Noise, helps further improving the high reflection rate measurement precision.

(2) mode (1) does not need trigger circuit, installs simplyr than mode (2), can effectively reduce system cost.

Description of drawings

Fig. 1 the present invention is based on the synoptic diagram that the straight chamber high reflection rate measurement device embodiment of card takes place function;

Fig. 2 for of the present invention without timing optimization input square wave (a) and optical cavity output signal (b) and carry out input square wave (c) and optical cavity output signal (d) behind the timing optimization by scheme (1);

Fig. 3 is a folded cavity configuration synoptic diagram of the present invention;

Optical cavity ring-down signal and the matched curve of Fig. 4 for surveying behind the timing optimization of the present invention;

Fig. 5 is the straight chamber high reflection rate measurement device synoptic diagram that the present invention is based on the threshold triggers circuit;

Fig. 6 for of the present invention without timing optimization input square wave (a) and carry out input square wave (b) and optical cavity output signal (c) behind the timing optimization by scheme (2);

Embodiment

Embodiment 1:

Embodiment 1 describes unlatching of the present invention in detail and turn-offs the timing optimization scheme (1) of laser beam.Fig. 1 the present invention is based on the straight chamber high reflection rate measurement device synoptic diagram that card takes place function.As shown in Figure 1, card 1, light source 2, spatial filtering and telescopic system 3, plano-concave high reflective mirror 4,5, lens 6, detector 7, data collecting card 8 and computing machine 9 compositions take place by function in measurement mechanism.Thick line among the figure is represented light path, and fine rule represents that signal wire links to each other.

Card 1 output two-way square-wave signal takes place in function, and one road square-wave signal is used to modulate the exciting current or the voltage of continuous semiconductor laser instrument 2, makes the laser output power square-wave frequency modulation, and square wave rising edge and negative edge be corresponding opening and closing laser beam respectively.Another road square-wave signal is used for trigger data acquisition card 8 record exponential damping signal after the square wave negative edge turn-offs laser beam.Spatial filtering and telescopic system 3 are made up of two lens and a pin hole, be used for laser beam reshaping with light source 2 output become basic mode and with the optical cavity pattern match, also can not adopt spatial filtering and telescopic system 3, promptly directly laser beam is coupled into optical cavity without pattern match.Two identical plano-concave high reflective mirrors 4,5, its concave surface plating high-reflecting film, reflectivity is greater than 99%, and concave surface constitutes straight chamber relatively.Laser beam is repeatedly reflection back output in the chamber, is received by detector 7 after lens 6 are assembled.Detector 7 converts light signal to electric signal.Turn-off laser beam simultaneously with the square wave negative edge, trigger pip trigger data acquisition card 8 writes down the exponential damping signals, and carries out data processing and storage by computing machine 9.Turn-off beam separation time Δ t ₂After open laser output again.Repeat above-mentioned steps and swing the repeatedly duplicate measurements of signal and high reflectance to realize declining.Card 1 takes place function and data collecting card 8 is directly controlled by computing machine 9 by pci bus.

Shown in Fig. 2 (a), before the timing optimization, card 1 output modulating frequency takes place function is f=1kHz, and dutycycle is 1: 1 a square-wave signal, and the cycle is 1/f=1ms.Corresponding optical cavity output signal is shown in Fig. 2 (b).Modulating frequency span before the timing optimization is 1Hz～1MHz, and the span of dutycycle P is 10000: 1～1: 100, and both make the square wave low duration greater than 5 times of ring-down times at the while value.Swing signal though the square wave negative edge closes can record to decline behind the laser instrument, because without timing optimization, it is generally less that the declining of negative edge swung signal amplitude, and signal to noise ratio (S/N ratio) is low, is unfavorable for the high-acruracy survey high reflectance.

The position that peak swing occurred in each cycle in the optical cavity ring-down signal is relatively stable, but certain random character is also arranged.Use Δ t ₁The moment that peak swing occurs in the expression one-period and the time interval between this cycle square wave rising edge, the Δ t in each cycle ₁Slightly different.Fig. 2 (b) has marked the position Δ t that one of them cycle peak swing occurs ₁

Represent a plurality of Δ t ₁Assembly average, also be the highest position of the peak swing frequency of occurrences, be used for optimizing modulating frequency and dutycycle.

The timing optimization mode (1) of unlatching of the present invention and shutoff laser beam has following three kinds of forms to realize the optimization of modulating frequency and dutycycle by the timing optimization that control modulating frequency f and dutycycle P realize laser beam switching:

(1) modulating frequency f remains unchanged, and dutycycle P becomes $P=\stackrel{\&OverBar;}{\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="S2007101224086E00011.png,S2007101224086E00031.png"\; state="\{\{state\}\}">t</figure-callout>}}_1}/\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="S2007101224086E00011.png,S2007101224086E00021.png"\; state="\{\{state\}\}">t</figure-callout>}}_2,$ Wherein $\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="S2007101224086E00011.png,S2007101224086E00021.png"\; state="\{\{state\}\}">t</figure-callout>}}_2=T-\stackrel{\&OverBar;}{\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="S2007101224086E00011.png,S2007101224086E00031.png"\; state="\{\{state\}\}">t</figure-callout>}}_1},$ T＝1/f；

(2) modulating frequency f becomes $f=P/\left[(1+P)\stackrel{\&OverBar;}{\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="S2007101224086E00011.png,S2007101224086E00031.png"\; state="\{\{state\}\}">t</figure-callout>}}_1}\right],$ Dutycycle P remains unchanged, and wherein the initial value of dutycycle satisfies $\stackrel{\&OverBar;}{\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="S2007101224086E00011.png,S2007101224086E00031.png"\; state="\{\{state\}\}">t</figure-callout>}}_1}/10000\mathrm{\&tau;}<P<\stackrel{\&OverBar;}{\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="S2007101224086E00011.png,S2007101224086E00031.png"\; state="\{\{state\}\}">t</figure-callout>}}_1}/5\mathrm{\&tau;};$

(3) modulating frequency f becomes $f=1/(\stackrel{\&OverBar;}{\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="S2007101224086E00011.png,S2007101224086E00031.png"\; state="\{\{state\}\}">t</figure-callout>}}_1}+\mathrm{\&Delta;}{t}_2),$ Dutycycle P becomes $P=\stackrel{\&OverBar;}{\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="S2007101224086E00011.png,S2007101224086E00031.png"\; state="\{\{state\}\}">t</figure-callout>}}_1}/\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="S2007101224086E00011.png,S2007101224086E00021.png"\; state="\{\{state\}\}">t</figure-callout>}}_2,$ Δ t wherein ₂Be the integral multiple of ring-down time τ, i.e. Δ t ₂=k τ, τ does not swing signal and determines that roughly the k value is determined on a case-by-case basis by carrying out declining of timing optimization, and scope is 5＜k＜10000.

Embodiment 1 adopts the optimization method of above-mentioned second kind of modulating frequency and dutycycle, and dutycycle is 1: 1, promptly $\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="S2007101224086E00011.png,S2007101224086E00021.png"\; state="\{\{state\}\}">t</figure-callout>}}_2=\stackrel{\&OverBar;}{\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="S2007101224086E00011.png,S2007101224086E00031.png"\; state="\{\{state\}\}">t</figure-callout>}}_1},$ As Fig. 2 (c) (d) shown in.Survey the Δ t in a plurality of cycles earlier ₁, and ask its assembly average

The modulating frequency that card output square wave takes place control function becomes it $f=1/2\stackrel{\&OverBar;}{\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="S2007101224086E00011.png,S2007101224086E00031.png"\; state="\{\{state\}\}">t</figure-callout>}}_1}.$ When this modulating frequency, signal averaging amplitude maximum is swung in declining of square wave negative edge trigger data acquisition card record.Swing signal input computing machine 9 by declining of data collecting card 8 records, match obtains straight chamber ring-down time τ ₁, as shown in Figure 3.By R=1-L/c τ ₁Calculate cavity mirrors reflectivity.Insert level crossing 10 to be measured, form folded cavity, as shown in Figure 4.Repeat said process, match obtains folded cavity ring-down time τ ₂, by R _x=exp (L/c τ ₁-L/c τ ₂) calculate flat mirror reflects rate to be measured.

Embodiment 2:

Embodiment 2 describes unlatching of the present invention in detail and turn-offs the timing optimization scheme (2) of laser beam.Fig. 5 is the straight chamber high reflection rate measurement device synoptic diagram that the present invention is based on the threshold triggers circuit.As shown in Figure 5, measurement mechanism is made up of light source 2, spatial filtering and telescopic system 3, plano-concave high reflective mirror 4,5, lens 6, detector 7, data collecting card 8, computing machine 9 and threshold triggers circuit 11.Thick line among the figure is represented light path, and fine rule represents that signal wire links to each other.

Embodiment 2 measurement mechanisms and Chinese patent application numbers 200610165082.0, publication number CN1963435A, the examples measure device of the patent of invention disclosed " method for measuring reflectance ratio of high reflected mirror " in open May 16 2007 date is identical, but embodiments of the invention 2 focus on illustrating the timing optimization method based on the laser beam switching of threshold triggers circuit.Light source 2 adopts the continuous semiconductor laser instrument.Spatial filtering and telescopic system 3 are made up of two lens and a pin hole, be used for laser beam reshaping with light source 2 output become basic mode and with the optical cavity pattern match, also can not adopt spatial filtering and telescopic system 3, promptly directly laser beam is coupled into optical cavity without pattern match.Two identical plano-concave high reflective mirrors 4,5, its concave surface plating high-reflecting film, reflectivity is greater than 99%, and concave surface constitutes straight chamber resonator cavity relatively.Laser beam is repeatedly reflection back output in resonator cavity, is received by detector 7 after lens 6 are assembled.Detector 7 converts light signal to electric signal, and outputs to data collecting card 8 and threshold triggers circuit 11 simultaneously.Threshold triggers circuit 11 is used for the size of comparison preset threshold and optical cavity output amplitude.When optical cavity output amplitude during greater than preset threshold, threshold triggers circuit 11 turn-off laser beam and simultaneously trigger data acquisition card 8 records turn-off exponential damping signal after the laser beam.Data collecting card 8 record exponential damping signals are also sent into computing machine 9 and are handled.Turn-off beam separation time Δ t ₃After open laser output again.Repeat above-mentioned steps and swing the repeatedly duplicate measurements of signal and high reflectance to realize declining.

In the present embodiment 2, exciting current or the voltage quick closedown laser output of threshold triggers circuit 11 by changing semiconductor laser, thus obtain the exponential damping signal.Also can and decline to swing and insert electric light or acoustooptic switch between the chamber, open or turn-off laser beam by threshold triggers circuit control photoswitch exciting current or voltage at laser instrument.

In the present embodiment 2, the square wave before the timing optimization is directly generated by the threshold triggers circuit, is used for the exciting current of semiconductor laser modulation, when the optical cavity output amplitude is turn-offed the exciting current of semiconductor laser during greater than threshold value.Square wave also can generate back input threshold triggers circuit by function generator (or function blocks), again by the exciting current modulation signal of threshold triggers circuit output as semiconductor laser.Square-wave frequency modulation frequency span is 1Hz～1MHz, and the span of dutycycle P is 10000: 1～1: 100, and both make the square wave low duration greater than 5 times of ring-down times at the while value.

Shown in Fig. 6 (a), before the timing optimization, threshold triggers circuit output modulating frequency is f=1kHz, and dutycycle is 1: 1 a square-wave signal, and the cycle is 1/f=1ms.It is 153mV that the threshold triggers circuit is provided with threshold value.When the optical cavity output signal during apart from the about 0.29ms of rising edge amplitude surpass threshold value, the threshold triggers circuit turn-offs the semiconductor laser exciting current fast, forms the square wave negative edge, shown in Fig. 6 (b).Negative edge obtains optical cavity exponential damping signal after turn-offing laser beam, shown in Fig. 6 (c).Dotted line is represented the threshold value that is provided with among Fig. 6 (c).Turn-off laser beam simultaneously with negative edge, threshold triggers circuit triggers data collecting card record exponential damping signal, and send into computing machine and carry out match and obtain ring-down time and reflectivity result.The processing of deamplification and chamber mirror, flat mirror reflects rate computation process to be measured are identical with embodiment 1.As experience a period of time Δ t ₃After, the rising edge of next square-wave cycle is opened laser beam, repeats above-mentioned steps and swings the repeatedly duplicate measurements of signal and high reflectance to realize declining.

The square-wave frequency modulation frequency remains unchanged in the present embodiment 2, f=1kHz.Because the particular location that each cycle spike occurs has certain random character, so the triggering in each cycle moment Δ t ₁Different.Δ t ₃The time interval that is carved into when triggering between the rising edge of next square-wave cycle is determined, so Δ t ₃Turn-off laser beam Δ t constantly with triggering ₁Change and passive change, i.e. Δ t ₃=1/f-Δ t ₁Also can be in the following ways: Δ t ₃Remain unchanged, value is the integral multiple of ring-down time τ, i.e. Δ t ₃=k τ, τ does not swing signal and determines that roughly the k value is determined on a case-by-case basis by carrying out declining of timing optimization, and scope is 5＜k＜10000.This moment, the square-wave frequency modulation frequency was turn-offed laser beam Δ t constantly because of triggering ₁Change and passive change, i.e. f=1/ (Δ t ₃+ Δ t ₁).

Claims (9)

1. the timing optimization method that is used for the laser beam switching of high reflection rate measurement, it is characterized in that: adopt function generator or function that the square-wave frequency modulation semiconductor laser of card output takes place, square wave rising edge and negative edge are corresponding respectively to be opened or the shutoff semiconductor laser, determines the moment of optical cavity output signal peak swing appearance and the time interval between the square wave rising edge

On this basis, optimize square-wave frequency modulation frequency f and dutycycle P or optimization square-wave frequency modulation frequency f or dutycycle P and make optical cavity output signal peak swing be in the square wave negative edge, thereby turn-off laser beam, while triggering collection exponential damping signal, elapsed time Δ t ₂After, open laser beam again by the square wave rising edge of next cycle, repeat said process and realize declining swinging the duplicate measurements of signal and high reflectance.

2. the timing optimization method that is used for the laser beam switching of high reflection rate measurement according to claim 1 is characterized in that: described employing square-wave frequency modulation semiconductor laser is realized by following approach: exciting current or voltage with the square-wave frequency modulation semiconductor laser realize opening or turn-offing laser beam.

3. the timing optimization method that is used for the laser beam switching of high reflection rate measurement according to claim 1, it is characterized in that: the initial value scope of described square-wave frequency modulation frequency f is 1Hz～1MHz, and the initial value scope of described dutycycle P is 10000: 1～1: 100.

4. the timing optimization method that is used for the laser beam switching of high reflection rate measurement according to claim 1 is characterized in that: the moment that described optical cavity output signal peak swing occurs and the time interval between the square wave rising edge

Be a plurality of Δ t ₁Assembly average, Δ t ₁The moment that peak swing occurs in the expression one-period and the time interval between this cycle square wave rising edge.

5. the timing optimization method that is used for the laser beam switching of high reflection rate measurement according to claim 1 is characterized in that: described optimization square-wave frequency modulation frequency f and dutycycle P or optimization square-wave frequency modulation frequency f or dutycycle P have one of following three kinds of forms to realize:

(1) modulating frequency f remains unchanged, and dutycycle P becomes

Wherein

T=1/f;

(2) modulating frequency f becomes

Dutycycle P remains unchanged, and wherein the initial value of dutycycle satisfies

(3) modulating frequency f becomes

Dutycycle P becomes

Δ t wherein ₂Be the integral multiple of ring-down time τ, i.e. Δ t ₂=k τ, τ does not swing signal and determines that roughly the k value is determined on a case-by-case basis by carrying out declining of timing optimization, and scope is 5＜k＜10000.

6. the timing optimization method that is used for the laser beam switching of high reflection rate measurement, it is characterized in that: by the square-wave frequency modulation laser beam of threshold triggers circuit output, the rising edge of square wave and negative edge are corresponding respectively to be opened or the shutoff laser beam, when optical cavity output amplitude during greater than pre-set threshold, the threshold triggers circuit turn-offs its output current fast and forms negative edge shutoff laser beam, while triggering collection exponential damping signal, elapsed time Δ t ₃After, open laser beam again by the square wave rising edge of next cycle, repeat said process and realize declining swinging the duplicate measurements of signal and high reflectance;

Described Δ t ₃Determine by following dual mode:

(1) the square-wave frequency modulation frequency remains unchanged, the Δ t in each cycle ₃The time interval that is carved into when triggering between the rising edge of next square-wave cycle is determined Δ t ₃Turn-off laser beam Δ t constantly because of triggering ₁Change and passive change, i.e. Δ t ₃=1/f-Δ t ₁

(2) Δ t ₃Remain unchanged, value is the integral multiple of ring-down time τ, i.e. Δ t ₃=k τ, τ does not swing signal and determines that roughly k value is determined on a case-by-case basis by carrying out declining of timing optimization, and scope is 5＜k＜10000, and this moment, the square-wave frequency modulation frequency was turn-offed laser beam moment Δ t because of triggering ₁Change and passive change, i.e. f=1/ (Δ t ₃+ Δ t ₁).

7. the timing optimization method that is used for the laser beam switching of high reflection rate measurement according to claim 6 is characterized in that: the initial value scope of described square-wave frequency modulation frequency f is 1Hz～1MHz.

8. the timing optimization method that is used for the laser beam switching of high reflection rate measurement according to claim 6, it is characterized in that: described threshold value is set by the threshold triggers circuit, adjustable between 5mV～5V, initial value is an optical cavity output signal peak-peak, can not trigger within a certain period of time as if the threshold value that is provided with and turn-off then automatic small size the downward modulation till triggering of threshold value of laser beam.

9. the timing optimization method that is used for the laser beam switching of high reflection rate measurement according to claim 6 is characterized in that: described square wave is generated by threshold triggers circuit itself or takes place to input to the threshold triggers circuit after card generates and by exporting after the threshold triggers circuit conversion by function generator or function.

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