CN1072354C - Beam direction microdrift detecting system - Google Patents

Abstract

The present invention relates to a micro-drift detecting system for beam directions, which is especially suitable for the detection of beam direction drift for laser recording systems with high precision; the micro-drift detecting system can also be used for the quantitative detection of vibration. The micro-drift detecting system mainly comprises two gratings with identical parameters, wherein the gratings are mutually parallel, and the centers of the gratings are put on a light axis of the system; a detected light source is put before the two gratings; a detector, a signal processor and a computer are arranged behind the two gratings. The detecting system of the present invention has the advantages of simple structure, small systemic error, direct measurement, high measuring precision (which can achieve the magnitude order of micro-radian), etc.

Description

Beam direction microdrift detecting system

The present invention relates to a kind of beam direction microdrift detecting system of beam direction high Precision Detection, be specially adapted to the detection of laser high-precision RW system beam direction drift, also can be used for detection by quantitative vibration.

In the prior art indirect method is often adopted in the detection of beam direction drift.

Prior art 1:

As shown in Figure 1, the photosurface of the light beam O direct illumination detector 2 (CCD or linear array photoelectric cell) of measured light 1 is measured its spot drift amount d by computing machine 3 sampling, calculates the direction drift value according to measured light 1 and sensitive detection parts 2 apart from p at last $\mathrm{\θ}=\frac{d}{p}$ 。But because p can not be excessive in actual applications, the precision of this method is subjected to the restriction of the resolution that detector can reach.Under the situation of p=1m, by having the detector that line element is of a size of 7～14 μ m now, its measuring accuracy only can reach 7～14 microradians, can not satisfy high-precision requirement.

Prior art 2:

As shown in Figure 2, between measured light 1 and detector 2, add telescopic system 4, carry out the angle with telescopic system 4 earlier and amplify, and then measure with said method.But according to Helmholtz's formula, when amplify at the angle, light beam will dwindle with identical multiple, influence the raising of measuring accuracy; And, add telescopic system 4 after, also very big to the influence of the energy distribution of elementary beam, this is the systematic error that is difficult to overcome.

In addition, two kinds of schemes all have another difficult problem more than: when measuring distance p, only know the photosurface of an end at detector, the other end may be difficult to accurate measurement in the inner somewhere of measured light.

Prior art 3:

As shown in Figure 3, for using the Taibo interferometer of Taibo (Talbot) effect and More (Moire) effect.Its basic structure mainly comprises two blocks of gratings 7,8, before first block of grating 7, form parallel beam by pointolite 5 emitted light beams through collimation lens 6 backs and enter grating 7, between grating 7 and grating 8, insert tested transparent substance 10, observation screen 9 is arranged after grating 8.If with 7,8 parallel placements of two blocks of gratings and dislocation mutually

Cycle then places the grating 8 at Taibo (Talbot) the plane place of grating 7 just in time to block the bright rays of the Talbot picture of grating 7, therefore forms details in a play not acted out on stage, but told through dialogues in grating 8 back.Insert tested transparent substance 10 between grating 7 and 8, will the light position by grating 7 be changed mutually, thereby form More (Moire) striped at film viewing screen, measure these stripeds, the position that can get tested transparent substance 10 distributes mutually.So the Taibo interferometer only is a kind of very delicate that the position distributes mutually of measuring.

The objective of the invention is to fully utilize the design feature of prior art 3 dexterously, the high Precision Detection system of the small drift of a kind of beam direction is provided in order to overcome the difficulty of prior art 1 and prior art 2.

Detection system of the present invention comprises that mainly being parallel to each other of two identical parameters is positioned over the locational grating 7,8 of system centre, and the center of two gratings 7,8 is just on the optical axis of system.Measured light 1 places before the grating 7, is equipped with collimating element 11 between measured light 1 and the grating 7.After grating 8, be equipped with detector 2, signal processor 12 and computing machine 3.Between grating 8 and detector 2, be equipped with beam-expanding element 13, as shown in Figure 4.If the spot size of measured light 1 emission light beam is enough big, do not need to expand again bundle, then between grating 8 and detector 2, just needn't put beam-expanding element 13, as shown in Figure 9.

Detection system as shown in Figure 4, when measured light 1 emission light beam was detected, metrological grating 7,8 was realized Tabo effect and Moire effect simultaneously; Tabo effect produces " from imaging ", and Moire effect is finished displacement and amplified.After detector 2 receives signal,, import computing machine 3 then and carry out computing and processing, draw testing result by 12 pairs of Moire fringe countings of signal processor and segmentation.

Above the said collimating element 11 that places between measured light 1 and the grating 7, can select lens, as shown in Figure 9; Or telescope assembly; Or vacancy, when promptly measured light 1 emission light beam being parallel beam, just needn't be again after measured light 1, before the grating 7 placement collimating element 11, as shown in Figure 8.

As shown in Figure 5, when parallel beam illumination grating 7, can be 1 then a series of Taibo pictures and magnification occurring thereafter.To space periodic is that the line grating talbot distance q (distance of Taibo picture and grating 7) of α satisfies

Q=m α ²/ λ (m=1,2,3 ...) λ is the wavelength of measured light 1 in (1) formula, m is a positive integer.

On the other hand, two line gratings are superimposed with each other, and the two grid line is intersected with low-angle, then can form Moire fringe, as shown in Figure 6.If the Taibo of grating 7 is α as the space periodic of grating 14 and grating 8, the grid line angle is β (β ≠ 0), then forms horizontal Moire fringe, and stripe displacement W satisfies: $W=\mathrm{\α}/2\sin \frac{\mathrm{\β}}{2}---\left(2\right)$ Promptly work as picture grating 14 along ox axle displacement α, then stripe displacement is W, and enlargement factor is $k=1/2\sin \frac{\mathrm{\β}}{2}\≈\frac{1}{\mathrm{\β}}---\left(3\right)$ When β was very little, k should be very big.The displacement amplification of Here it is Moire fringe.

As shown in Figure 7, grating 7 from imaging grating 14 and grating 8 on same plane, constitute moire grating and pay.Comparison diagram 7 (a), two kinds of situations of 7 (b) know that beam direction changes correspondingly to utilize Moire effect as the moving of grating 14,8 relative displacements, and can directly measure the displacement of having amplified.

Further theoretical analysis shows: if certain section time beam direction is along ox axle drift θ _x, then the relative displacement as grating 14, grating 8 is x=q θ _x(q is the talbot distance of grating 8 place faces) after Moire effect is amplified, produces displacement $X={\mathrm{kq\θ}}_x=\frac{q}{\mathrm{\β}}{\mathrm{\θ}}_x---\left(4\right)$ Repeatedly sampling can obtain a series of θ _xValue.θ theoretically _xShould satisfy normal distribution (Gaussian distribution), make numerical value and calculate, can provide the direction drift angle Θ of light beam along ox _xIf the no tendentiousness of beam direction drift, Θ _xBe reflected collimated light beam direction drift angle Θ.

Measure the axial direction drift of ox θ _xAfter, can be with two gratings half-twist again, measure a series of θ in that y is axial _y, can calculate drift angle Θ equally _yAt last, can according to circumstances handle two data: or ask average, or get the greater, or record respectively, or continue other direction is measured.

The advantage of detection system of the present invention:

Systematic survey beam direction drift angle of the present invention has following advantage: one, and simple in structure, optical system can only be introduced two blocks of gratings fully, and systematic error is little; Its two, measure more directly because grid line angle β and talbot distance q, can according to circumstances select, as the parameter of system, the displacement X that measures Moire fringe can calculate angle drift θ _xIts three, technical foundation is good, has suitable proven technique to utilize to the counting and the segmentation of Moire fringe; Its four, the measuring accuracy height can reach the microradian magnitude; At last, detection is shorter, easy to use with the distance of measured light 1.

Description of drawings:

Fig. 1: be the ordinary construction synoptic diagram of the detection beam direction of prior art 1 drift.

Fig. 2: utilize the angle for prior art 2 and amplify the structural representation that detects.

Fig. 3: be the structural representation of prior art 3 Taibo interferometers.

Fig. 4: be detection system basic structure synoptic diagram of the present invention.

Fig. 5: be the Tabo effect synoptic diagram.

Fig. 6: be the Moire effect synoptic diagram.

Fig. 7: for detection case is analyzed synoptic diagram.

Wherein Fig. 7 a is the situation of light beam normal incidence in grating 7, and Fig. 7 b is the situation of light beam oblique incidence in grating 7, and variation has taken place in the Taibo image position of grating 7 under two kinds of situations as can be seen.

Fig. 8: be the used detection system structural representation of embodiment 2.The beam-expanding element 13 that wherein inserts between grating 8 and the detector 2 is lens.

Fig. 9: be the used detection system structural representation of embodiment 4.Between measured light 1 and grating 7, insert a short focal length lens as collimating element 11.

Embodiment 1:

As shown in Figure 4, be the parallel beam of diameter R for the light beam of measured light 1 greater than 1mm, can allow light beam pass through grating 7,8, directly measure, do not need collimating element 11 and beam-expanding element 13, can obtain satisfied result.

If R=2mm, a=0.02mm is for guaranteeing to observe 2 Moire fringes in the visual field, the desirable 0.02rad of grid line angle β.If detector 2 selects CCD for use, its pixel dimension is 14 μ m, talbot distance q=200mm, and then the stripes not match line further segments its measuring accuracy and can reach 1.4 μ rad.

Embodiment 2:

As shown in Figure 8, if hot spot can select for use lens to insert between gratings 8 and the detector 2 as beam-expanding element 13 less than 1mm, to the Moire fringe amplification, sampling processing again can remedy the shortcoming of Moire fringe enlargement factor deficiency like this.

Embodiment 3:

As shown in Figure 4, if grating 7,8 is the orthogonal grating of identical parameters, detector 2 is selected area array CCD for use, and computing machine 3 can once be measured angle drift Θ in ox axle and oy axle two direction sampling processing _x, Θ _y

Embodiment 4:

As shown in Figure 9, the light beam of measured light 1 is the spherical wave of dispersing.If directly detect, then the adjustment process of system is complicated; Can add a short focal length lens as collimating element 11 this moment between measured light 1 and grating 7, light beam is changed into parallel beam detect.

Embodiment 5:

Detect mechanical vibration state with detection system of the present invention.Structure as shown in Figure 4, require one the emission light beam the good light source of directional stability, then can on the position of measured light 1, put this reliable and stable light source, the system of Gou Chenging can be used as new system like this.It is positioned over the place of detected vibration state, can reflects the mechanical vibration situation at this place by measurement data.

Claims (1)

1. beam direction microdrift detecting system, the grating (7 that comprises two identical parameters, 8) be on the center of the system that is placed in parallel to each other, and two gratings (7,8) center is on systematic optical axis, measured light (1) is to place on first block of grating (7) systematic optical axis before, detector (2) is to place on second block of grating (8) systematic optical axis afterwards, it is characterized in that second block of grating (8) place the distance first block of grating (7) for talbot distance q on the plane of imaging grating (14), the light beam that is incident on first block of grating (7) must be a parallel beam, or between measured light (1) and first block of grating (7), be equipped with collimating element (11), at detector (2) signal processor (12) and computing machine (3) are arranged afterwards.

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