CN102095498A - High-accuracy Fourier transformation measuring method of scanning type - Google Patents

Abstract

The invention relates to a high-accuracy Fourier transformation measuring method of a scanning type, belonging to the technical fields of computer measurement and photoelectrons. Through using an embedded monolithic computer, a phase-locked doubling circuit and an LCD (Liquid Crystal Display), the method comprises the following steps of: amplifying and doubling the frequency of an interference signal of reference light to be a pulse signal with higher frequency to trigger the analog-to-digital conversion of an embedded computer on the interference signal of measured light; then, carrying out Fourier transformation to acquire and display signal spectrogram on the LCD; comparing with the frequency spectrum of the reference light signal, calculating the accuracy value of the center frequency of each measured spectrum line and displaying on the LCD; and triggering the analog-to-digital conversion of the interference signal of the reference light according to the interference signal of the reference light to fully counteract time base errors brought by an unstable motor speed in signal acquisition so that the center frequency of the spectrum is accurately calculated. The embedded computer finishes signal acquisition, Fourier transformation and pattern and digit display so that the spectrograph electronic system has small size, low cost and high accuracy.

Description

A kind of method of scan-type high precision Fourier transform measure spectrum

Technical field

The present invention is a kind of method of scan-type high precision Fourier transform conversion measure spectrum, belong to computer measurement and photoelectron technology field, can be used to measure multimode laser output mode, the centre frequency of each pattern is carried out precision measurement, also be used for the luminous or reflective spectral distribution of Measuring Object and typical characteristic spectral line frequency (wavelength) is calculated exact value, important effect is arranged at spectral investigation and material composition analysis field.

Background technology

In laser technology and spectroscopy applications field, laser instrument longitudinal mode, each pattern center frequency value accurately are important parameters very to technician and slip-stick artist.Especially in the material field of detecting, luminous or be excited the precision measurement of reflective spectrum and be the object analysis composition, distinguish the gordian technique of trace element to object.

In spectral measurement and spectral analysis research field, generally adopt grating spectrum, grating spectrum resolution is lower.The Fourier transform spectrometer adopts computing machine, and spectral resolution is higher.

Summary of the invention

The objective of the invention is to overcome the above-mentioned shortcoming of existing spectrometer, a kind of method of scan-type high precision Fourier transform measure spectrum is provided, use this method to measure tested light frequency, eliminated the influence of motor speed to measuring accuracy, simultaneously, also improved measuring accuracy, and can expand to infrared measurement range and visible-range.

Technical scheme of the present invention is as follows: the method for the measure spectrum among the present invention is to realize by scanner, described scanner comprises michelson interferometer optical path part and circuit part, described circuit part comprises first amplifier, second amplifier, comparer, frequency multiplier, processor and the display device that is connected with processor, wherein: first amplifier, comparer, frequency multiplier, processor connects successively, the output terminal of second amplifier directly links to each other with processor by pole changer, and the output terminal of first amplifier also directly links to each other with processor by this pole changer;

Use the tested light frequency of above-mentioned spectrometer measurement, its step is as follows:

1) will be by photometry and reference light input michelson interferometer optical path, reference light after interfering through michelson interferometer optical path and received by first photelectric receiver, 5 second photelectric receivers 8 respectively by photometry, and convert thereof into digital data transmission and handle to circuit part;

2) electric signal of first photelectric receiver output is successively by inputing to processor A D sampling trigger end behind first amplifier, comparer, the frequency multiplier, and the electric signal of second photelectric receiver, 8 outputs directly inputs to the AD sampled signal input end of processor after by second amplifier;

3) adjust switch, the output terminal of first amplifier directly is connected with processor, processor is gathered the voltage signal of NUM point of reference light, and NUM must be more than or equal to 2 ²⁰, and the signal after will gathering handles the frequency spectrum that obtains reference light, this frequency spectrum delivered to display device show, reads the position N of the pairing point of peak value of reference light from the frequency spectrum that shows _r(N _rThe N of expression reference light, literary composition is seen below in the explanation of N), according to formula Calculate with reference to light frequency, wherein: f _sIt is the sample frequency of reference light;

4) adjust switch, second amplifier directly is connected with processor, being amplified the back by the electric signal of photometry through second amplifier is gathered by processor, reference optical signal is successively through inputing to the AD sampling trigger end of processor behind first amplifier, comparer, the frequency multiplier, gather the trigger pip of tested light signal as processor, processor is gathered by the voltage signal of the NUM of photometry point, its sample frequency f _sIdentical with the sample frequency and the number of samples of reference light with number of samples NUM, the tested light signal that processor will collect is handled and is obtained the tested frequency spectrum of examining light, and delivers to the display device demonstration;

5) read by the position N of the pairing point of the peak value of photometry from the tested optical spectrum that shows _u(N _uExpression is by the N of photometry, and literary composition is seen below in the explanation of N), according to formula

Calculate tested light frequency.

Spectrum measurement method among the present invention and motor speed are irrelevant, below its principle are described:

The measurement light path that the present invention uses adopts interfere type, based on the Michelson principle of interference: the two-beam mutual superposition, produce interference fringe, the waveform of the reference laser of comparison given frequency and the tested interference of light signal of unknown frequency, utilize embedded computer to gather the simulating signal of fringe intensity, and do Fourier transform and can obtain by the spectrum of photometry accurate Calculation core frequency values.

Be reduced to monochromatic light by photometry, interfere back signal intensity I _Out(t) be:

$I_{\mathrm{out}}\left(t\right)=\frac{I_0}{2}[1+\cos \left(\frac{{2\mathrm{\πf}}_u{\mathrm{\υ}}_0}{c}t\right)]---\left(1\right)$

I ₀Be the amplitude of tested interference of light stripe signal intensity, υ ₀Be motor speed, f _uBe tested light frequency, c is the light velocity.The frequencies omega of tested optical interference signals _u:

ω _u＝2πf _uυ ₀/c (2)

As accompanying drawing 2.Reference light amplifies the reference optical signal that first photo-detector 5 receives, obtain pulse signal after the frequency multiplication through treatment circuit, this pulse signal is the analog-to-digital trigger pip of tested optical interference signals, as reference laser is carried out the collection of interference signal, obtain the interference signal frequencies omega of reference light _r:

ω _r＝2πf _rυ ₀/c (3)

In the following formula: f _rBe with reference to light frequency, ω _rBe a fixed value, when spectral measurement begins, demarcate and to obtain.According to (2), (3) formula, can obtain:

$f_u=\frac{{\mathrm{\ω}}_u}{{\mathrm{\ω}}_r}{f}_r---\left(4\right)$

By (4) formula as can be seen, the frequency accuracy of tested interference of light signal only depends on reference light precision, irrelevant with motor speed.Have the function of the calculating of spectrum demonstration and spectrum line peak center frequency, measuring accuracy maintains six precision.

Again, light frequency f is by position N, sampling number NUM and the sample frequency f of the pairing point of peak value _sDecision.

$f=\frac{N}{\mathrm{NUM}}{f}_s---\left(5\right)$

The implication of N is seen accompanying drawing 4, and the pairing horizontal ordinate of counting of expression peak value promptly peak value occurs at N some place.

This be because when sampling number be NUM, when sample frequency is fs, its precision is

Light frequency is exactly the position N of the pairing point of peak value and the product of precision.

Corresponding to tested light frequency, have so

$f_u=\frac{N_u}{\mathrm{NUM}}{f}_s---\left(6\right)$

In the following formula: N _uBy the position of the pairing point of the peak value of photometry;

For the reference light frequency, have

$f_r=\frac{N_r}{\mathrm{NUM}}{f}_s---\left(7\right)$

In the following formula: N _rIt is the position of the pairing point of peak value of reference light;

By (6), (7) formula,

$f_u=\frac{N_u}{N_r}{f}_r---\left(8\right)$

For (8) formula, N _rCan be by measuring f _rFor the reference light frequency known, tested optical frequency point position N _uCan directly read from the image that outputs to liquid crystal display LCD, substitution (8) formula is tried to achieve tested light frequency f _uValue.

High-accuracy measurement of the research field of spectral analysis and measurement and laser or metering field need the more spectral measurement and the demonstration of high precision, wider scope, traditional grating spectrum reaches capacity, the present invention adopts embedded computer, make and measure intellectuality, precision improves a lot, showing the light frequency of spectrum and spectral line peak correspondence simultaneously with liquid crystal display, is the multi-wavelength measuring system of a light.

1. the present invention adopts embedded computer, and by the number conversion of external trigger control internal mode, the demonstration of the spectrum that computed fast fourier transform realizes also shows spectral line peak center frequency computation part.Circuit diagram 2 of the present invention is made up of embedded monolithic computing machine, phase locking frequency multiplying circuit and LCD.The interference signal of reference laser carries out frequency multiplication through amplifying, adopt phaselock technique, becomes the higher pulse signal of frequency and goes to trigger the analog to digital conversion of embedded computer to tested optical interference signals, carries out Fourier transform then and obtains the signal spectrogram and show on LCD.Frequency spectrum with reference optical signal compares again, can calculate the exact value of the centre frequency of the tested spectrum line of each bar, and show on LCD.Trigger the analog to digital conversion of tested optical interference signals according to the reference light interference signal, can offset the motor speed non-stabilized zone fully and come the signals collecting time base error, make that the spectral centroid frequency computation part is accurate.By embedded computer finish signals collecting, Fourier transform, the figure numeral shows, make that spectrometer electronic system volume is little, cost is low, stable, precision is high.

2. in order to guarantee that measuring accuracy is 10 ^-6More than, the DATA REASONING of each Fourier transform all guarantees to gather by the analog to digital conversion of photometry 2 ²⁰The fixed numbers that point (being the NUM value) is above.And calculate frequency spectrum fast in the inner FFT technology that adopts of embedded computer, and show.

3. amplify the analog to digital conversion of the signal triggering embedded computer behind the phase locking frequency multiplying by the reference light interference signal, offset the error that motor speed brings fully, reach sampled data points recited above after, embedded computer calculates frequency spectrum, and shows.

4. the reference laser frequency values of measuring according to timing signal can entirely accurate calculate by each core frequency values of photometry.Reference laser is that Frequency Stabilized Lasers, frequency values are known, and the NUM value is known, by determining to be presented at the frequency position N of the frequency spectrum on the LCD _uValue draws with (8) formula accurate Calculation.

5. the present invention adopts the Michelson interfere type, solves the not high problem of resolution, and can expand to infrared measurement range and visible-range.In addition, reference optical signal control sample frequency is that reference optical signal and tested light signal are synchronous, can offset the error that the motor speed shakiness is brought fully.

Description of drawings

The light path principle figure of Fig. 1 spectrometer;

The signals collecting of Fig. 2 spectrometer and processing block scheme;

Fig. 3 spectrometer measurement shows implements circuit diagram;

The implication synoptic diagram of the position N of the pairing point of Fig. 4 peak value;

Among the figure: 1, reference laser, 2, spectroscope, 3, first catoptron, 4, first prism of corner cube, 5, first photelectric receiver, 6, second catoptron, 7, second prism of corner cube, 8, second photelectric receiver, 9, removable prism objective table, ← reference light light path ← by the photometry light path

Embodiment

The present invention will be further described below in conjunction with accompanying drawing.

According to the Michelson principle, the spectrometer light path layout as shown in Figure 1.Wherein the canonical reference light source adopts frequency stabilized laser, and the degree of stability of its frequency has determined the spectral measurement precision of spectrometer.Reference laser is identical with the light path that is formed interference fringe by photometry separately.Be example only, the forming process of interference signal is described with the reference light.1 ° of reference light source output beam, through spectroscope 2, be divided into transmitted light 1 ' and reflected light 2 ' at the A point, transmitted light 1 ' is through first catoptron 3, enter movable first corner cube reflector 4, turn back to first catoptron 3 from first corner cube reflector 4 again, reflected light 1 through 3 " get back to spectroscopical B place and reflex to first photelectric receiver 5; Simultaneously reflected light 2 ' is behind second catoptron 6 and second corner cube reflector 7, again through 6 reflected light 2 " also turn back to B place, light beam 1 " and 2 " converge at the B point, interfere, by 5 receptions of first photo-detector, as the collection point of the interference signal of reference signal.

By photometry optical splitting point B place, close luminous point at the A place, interference signal is received by second photo-detector 8.When spectrometer was worked, drive motor dragged removable prism objective table 9 and comes and goes translation vertically, made reference laser and was produced optical path difference by photometry, interfered phenomenon, and first photodetector 5 and second photodetector 8 can receive interference signal.

Through treatment circuit with the signal of first photo-detector 5 amplify, frequency multiplication obtains pulse signal, this pulse signal is the analog-to-digital trigger pip of tested optical interference signals, can offset the inhomogeneous of in scanning process motor speed like this.Obtain by the spectrum of photometry through data acquisition and Fourier transform.

The canonical reference light source adopts 633nm inner chamber type He-Ne laser instrument, utilizes two longitudinal mode thermal control frequency-stabilizing methods to carry out frequency stabilization, and the degree of stability of its wavelength is 10 ^-8Magnitude, repdocutbility is better than 2 * 10 ^-7Removable prism is a prism of corner cube, be fixed on the guide rail, prism of corner cube can come and go and move around, and making on the win photodetector 5 and second photodetector 8 and producing interferometric fringe signal is respectively reference laser (Ref_Laser) and by photometry (Unkn_Light).Optoelectronic switch is installed at two ends at guide rail, detects the commutation action of prism, is monitored by embedded computer simultaneously.

Circuit as shown in Figure 3, U1 is DSP (TMS320F2812) digital signal processor, U2 is the LCD display driver chip, LCD is 10 cun of a RS485 interface colored liquid crystal displays, the resolution 800*640 of showing; U3 is the phase locking frequency multiplying chip, is 16 times of reference laser interference signal (Ref_Laser) by the feasible square-wave signal frequency of exporting from 9 pin of U3 of 16 frequency divisions of U4.This square-wave signal frequency has determined by the sample frequency of photometry.

The spectral measurement process is as follows:

Gate S1 selects by photometry.After 149 pin (external interrupt 1 signal) of DSP obtain the commutation actuating signal of prism, begin to start the analog to digital conversion that external interrupt 2 (151 pin of U1) removes to trigger ADC0 (tested optical interference signals).In order to guarantee precision, sampling number NUM must be more than or equal to 2 ²⁰AD translation data number reaches 2 ²⁰Stop the AD conversion, carry out the FFT computing, the frequency spectrum that obtains is exactly a spectrum, and this spectrum is exported to LCD by RS485 and shown, reads the pairing frequency of peak value position from the spectrum that shows.

Definite process of spectrum line centre wavelength is as follows:

At first, demarcate: S1 selects the reference light of given frequency.Repeat the DSP program process of " spectral measurement process ", from the spectrum that shows, read the pairing frequency of reference light FFT maximal value position, be designated as N _r

Then, S1 selects by photometry.Repeat the DSP program process of " spectral measurement process ", from the spectrum that shows, read, be designated as N by the pairing frequency of photometry FFT maximal value position _uThrough type (8) formula calculates the pairing frequency of spectrum line (wavelength), and shows on LCD.

The actual measurement effect: machine debugging is good, adopts the 532nm green glow to carry out actual test respectively as tested Frequency Stabilized Lasers, and reference light is the 633nm Frequency Stabilized Lasers, degree of stability 10 ^-8, preceding 7 632.9914nm of vacuum medium wavelength.Once gather the simulating signal of 1048576 tested interference of light, spectrum can clear being presented on the LCD, and single longitudinal mode 532nm green glow spectral line bearing accuracy is as 532.2452nm, precision 10 ^-6Measuring rate per 2 seconds 1 time can show spectrum and spectral line center line wavelength value simultaneously.

Claims (1)

1. the method for a scan-type high precision Fourier transform measure spectrum, it is characterized in that, this method realizes by scanner, described scanner comprises michelson interferometer optical path part and circuit part, described circuit part comprises first amplifier, second amplifier, comparer, frequency multiplier, processor and the display device that is connected with processor, wherein: first amplifier, comparer, frequency multiplier, processor connects successively, the output terminal of second amplifier directly links to each other with processor by pole changer, and the output terminal of first amplifier also directly links to each other with processor by this pole changer;

Use the tested light frequency of above-mentioned spectrometer measurement, its step is as follows:

1) will be by photometry and reference light input michelson interferometer optical path, reference light after interfering through michelson interferometer optical path and received by first photelectric receiver (5) second photelectric receivers (8) respectively by photometry, and convert thereof into digital data transmission and handle to circuit part;

2) electric signal of first photelectric receiver output is successively by inputing to processor A D sampling trigger end behind first amplifier, comparer, the frequency multiplier, and the electric signal of second photelectric receiver (8) output directly inputs to the AD sampled signal input end of processor after by second amplifier;

3) adjust switch, the output terminal of first amplifier directly is connected with processor, processor is gathered the voltage signal of NUM point of reference light, and wherein NUM is more than or equal to 2 ²⁰, and the signal after will gathering handles the frequency spectrum that obtains reference light, this frequency spectrum delivered to display device show, reads the position N of the pairing point of peak value of reference light from the frequency spectrum that shows _r, according to formula

Calculate with reference to light frequency, wherein: f _sIt is the sample frequency of reference light;

4) adjust switch, second amplifier directly is connected with processor, being amplified the back by the electric signal of photometry through second amplifier is gathered by processor, reference optical signal is successively through inputing to the AD sampling trigger end of processor behind first amplifier, comparer, the frequency multiplier, gather the trigger pip of tested light signal as processor, processor is gathered by the voltage signal of the NUM of photometry point, its sample frequency f _sIdentical with the sample frequency and the number of samples of reference light with number of samples NUM, the tested light signal that processor will collect is handled and is obtained the tested frequency spectrum of examining light, and delivers to the display device demonstration;

5) read by the position N of the pairing point of the peak value of photometry from the tested optical spectrum that shows _u, according to formula

Calculate tested light frequency.

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