CN105136295A - Solution method and apparatus for spectrum non-uniformity in same image of AOTF - Google Patents

Abstract

The invention relates to the technical field of AOTF spectrum imaging, and more specifically relates to a solution method and an apparatus for spectrum non-uniformity in the same image of an AOTF. The solution method is mainly used for solving spectrum non-uniformity of the same image in the imaging of the AOTF and is a method for realizing spectrum correction via subsequent data processing, and the central wavelength of AOTF diffraction corresponding to a pixel xi in the x direction of any CCD with any driving frequency f is obtained via a formula shown in the description. The solution method and the apparatus are mainly applied to spectrum imaging of the AOTF, compared with the conventional AOTF imaging spectrum, the average error of the spectrum in the same image can reduce one order of magnitude, and the spectrum measuring precision of the AOTF is obviously improved.

Description

The solution that in a kind of AOTF same width figure, spectrum is uneven and device

Technical field

The present invention relates to AOTF spectral imaging technology field, more specifically, relate to solution and device that in a kind of AOTF same width figure, spectrum is uneven, the spectrum being mainly used to solve same width figure in AOTF imaging is uneven, is a kind of method being realized middle-low alloy steels by follow-up data process.

Background technology

Acousto-optic tunable filter (Acousto-optictunablefilter, AOTF) has that volume is little, tuned speed is fast, spectral range is wide, diffraction efficiency advantages of higher.Imaging spectrometer based on AOTF is applied in remote sensing, environmental monitoring, biomedicine and food inspection.

In AOTF, spectral measurement precision plays critical effect to light spectrum image-forming quality.In practical study, for AOTF imaging spectral, when light impinges perpendicularly in AOTF, a certain fixing wavelength that its a certain driving frequency is corresponding.But the light of space diverse location target can not all vertical incidence, this just causes the incident angle entering AOTF light different, thus cause its diffraction centre wavelength of the light of different incidence angles also to change, make CCD diverse location detect the light of different diffraction wavelength.And in existing survey AOTF imaging spectral, the detection of CCD diverse location obtains: during vertical incidence, the light of wavelength corresponding to fixed drive frequency.Certain error is there is in this with regard to making the measurement of theoretical spectral measurement and actual spectrum.Pursuing today of high precision spectral measurement, thisly can not to be ignored by theoretical and the actual error brought.So propose the method that can improve AOTF spectral measurement precision by theoretical and experimental study, the method can reduce measuring error to greatest extent, for later high precision spectral measurement is laid a good foundation.

Summary of the invention

In order to overcome the problem that in prior art, in AOTF imaging, same width figure spectrum is uneven, the invention provides and a kind ofly adopt quadratic fit to revise the method for spectrum, thus improve the measuring accuracy of AOTF spectrum.

In order to solve the problems of the technologies described above, the technical solution used in the present invention is:

The solution that in a kind of AOTF same width figure, spectrum is uneven, in the spectral range and angular range of AOTF, under any driving frequency f, diffraction central wavelength lambda (f in incident angle α and this situation, α) can parabolic relation be approximately, be specially:

λ(f,α)＝Aα ²+λ ₀(f)(1)

In above formula, AOTF diffraction light centre wavelength when λ (f, α) is driving frequency is f, incident angle is α; λ ₀f () is driving frequency diffraction light centre wavelength when being f, vertical incidence AOTF; Described λ ₀f (), for carrying when AOTF dispatches from the factory, also can adopt polychromatic light vertical incidence AOTF and be recorded by high resolution spectrometer; Described A adopts following steps to obtain:

AOTF is placed on high-accuracy angle measurement unit and makes the n of AOTF in a spectral range driving frequency f respectively ₁, f ₂, f ₃... f _nlower work, for each driving frequency f _nunder, parallel polychromatic light by AOTF diffraction, and is obtained the diffraction wavelength λ (f under different incidence angles α by high resolution spectrometer _n, α), to α and λ (f _n, α) and carry out least square fitting, and require that quafric curve must be crossed [α=0, λ ₀(f _n)] point, the A obtained after matching _n, A _nfor A in (1) formula, can approximate representation be:

A _n＝Bλ ₀(f _n)+C(2)

B and C in above-mentioned (2) formula can by the n obtained above (λ ₀(f ₁), A ₁), (λ ₀(f ₂), A ₂), (λ ₀(f ₃), A ₃) ... (λ ₀(f _n), A _n) adopt least square fitting to obtain, in conjunction with above-mentioned (1) formula and (2) Shi Ke get:

λ(f,α)＝[Bλ ₀(f)+C]α ²+λ ₀(f)(3)

Because CCD is placed in the focus of imaging len, so the picture dot x of CCD _iwith the pass of the focal length F of incident angle α and imaging len be:

$\mathrm{\α}=arctan\left(\frac{il}{F}\right)---\left(4\right)$

In above formula, l is the length of side of CCD picture dot; I Wei Yi CCD center is 0 at diffraction direction picture dot x _isequence number;

In λ (f, α), λ is the function about f and α, λ (f, x _i) in λ be relevant f and picture dot x _ithe function of sequence number i, therefore can obtain the picture dot x of any driving frequency f, arbitrarily CCD by above-mentioned (4) formula (3) formula of bringing into _ithe centre wavelength of corresponding A OTF diffraction:

$\mathrm{\λ}(f,x_i)=\[{\mathrm{B\λ}}_0\left(f\right)+C\]{\arctan }^2\left(\frac{il}{F}\right)+{\mathrm{\λ}}_0\left(f\right)---\left(5\right).$

Described high-accuracy angle measurement unit is spectroscope, described spectroscope angle-measurement accuracy 1'=0.0167 °.

The solving device that in a kind of AOTF same width figure, spectrum is uneven, comprise preposition optical system, the first polaroid, diaphragm, AOTF, the second polaroid, imaging len, CCD and computing machine, described preposition optical system is made up of the first lens, the second lens and the 3rd lens, and described first lens, the second lens, the 3rd lens, the first polaroid, diaphragm, AOTF, the second polaroid, imaging len, CCD and computing machine are arranged in order.

The polarization direction of described first polaroid and the second polaroid is orthogonal.

The beneficial effect that compared with prior art the present invention has is:

The present invention adopts quadratic fit to revise the problem that in AOTF imaging, same width figure spectrum is uneven, and compared with existing AOTF imaging spectral, the average error of same width figure spectrum can reduce an order of magnitude, significantly improves the spectral measurement precision of AOTF.

Accompanying drawing explanation

Below by accompanying drawing, the specific embodiment of the present invention is described in further detail.

Fig. 1 is the basic index path of apparatus of the present invention;

Fig. 2 is AOTF angle of diffraction spectral distribution graph of the present invention;

Fig. 3 is CCD polishing wax distribution schematic diagram;

Fig. 4 is driving frequency when being 116MHz vertical incidence, reality and revised numerical value schematic diagram;

Fig. 5 is driving frequency when being 120MHz vertical incidence, reality and revised numerical value schematic diagram;

Fig. 6 is driving frequency when being 136MHz vertical incidence, reality and revised numerical value schematic diagram;

Fig. 7 is driving frequency when being 140MHz vertical incidence, reality and revised numerical value schematic diagram.

In figure: 1 be diaphragm for preposition optical system, 2 is the first polaroid, 3,4 be imaging len for AOTF, 5 is the second polaroid, 6,7 be CCD, 8 be the 3rd lens for computing machine, 9 be the first lens, 10 is the second lens, 11.

Embodiment

The invention will be further described by reference to the accompanying drawings for embodiment below.

As shown in Figure 1, the solving device that in a kind of AOTF same width figure, spectrum is uneven, comprise preposition optical system 1, first polaroid 2, diaphragm 3, AOTF4, the second polaroid 5, imaging len 6, CCD7 and computing machine 8, preposition optical system 1 is made up of the first lens 9, second lens 10 and the 3rd lens 11, measured target light is successively after preposition optical system 1, first polaroid 2 and diaphragm 3 at a distance, enter AOTF4 diffraction to filter, by the second polaroid 5, be imaged on CCD7 through imaging len 6, finally by computing machine 8 by middle-low alloy steels.

Preposition optical system 1 is compressed to by distant place measured target angle of light within the scope of the field angle of AOTF4 permission, and a kind of parallel beam is become another kind of parallel beam, sees Fig. 1.Because measured target distance AOTF imaging spectrum system is distant, add the restriction of diaphragm 3, diverse location target can be similar to and see as: under different field angle, a branch of very thin parallel beam.The namely measured target of distant place diverse location, the incident angle entering AOTF imaging spectrum system is different, and then the incident angle entering AOTF4 after preposition optical system 1 is different, is imaged on the different picture dot of CCD7, as shown in Figure 1 through imaging len 6; Again due to when fixed drive frequency, AOTF4 diffraction wavelength is relevant with the angle of incident AOTF4, and wavelength just can be revised in therefore different with CCD7 according to the focal length of imaging len 6 picture dot positions, as shown in Figure 2.

The polarization direction of described first polaroid 2 and the second polaroid 5 is completely orthogonal, mainly in order to eliminate in AOTF4 0 grade and-1 order diffraction light to the impact of AOTF light spectrum image-forming.

As shown in Figure 2, suppose that AOTF diffraction direction is x direction, because AOTF4 only has the centre wavelength of diffraction direction relevant with incident angle, the practical center wavelength of the different picture dots therefore on CCD7 as shown in Figure 3.

Due to impacts such as crystal pro cessing precision, installation accuracies, there is some difference for the AOTF that actual production goes out and theoretical meeting, therefore for the AOTF4 of reality, under each driving frequency, the relation entering AOTF4 diffraction centre wavelength and incident angle can adopt the spectrometer of High-precision angle measurement mechanism and high spectral resolution to record, due under will recording each driving frequency, diffraction centre wavelength corresponding to different incidence angles, quantities is very large, therefore adopts the mode of matching.Specific as follows: actual AOTF, due in certain spectral range and angular range, can parabolic relation be approximately for diffraction wavelength λ (f, α) in incident angle α under any driving frequency f and this situation, and about incident angle α=0 ° both sides symmetry:

λ(f,α)＝Aα ²+λ ₀(f)(1)

In above formula, AOTF4 diffraction light centre wavelength when λ (f, α) is driving frequency is f, incident angle is α; λ ₀f () is driving frequency diffraction light centre wavelength when being f, vertical incidence AOTF; λ ₀f () is also the wavelength that existing AOTF imaging spectral generally adopts, do not consider the impact of incident angle α.

Wherein, in (1) formula, λ ₀f () producer when buying AOTF can provide, or also can adopt polychromatic light vertical incidence AOTF and be recorded by high resolution spectrometer.

Wherein, (1) in formula, A can adopt high resolution spectrometer and High-precision angle measurement mechanism measurement data least square fitting to obtain, concrete grammar is: be placed on high-accuracy angle measurement unit AOTF4 (as spectroscope, angle-measurement accuracy 1'=0.0167 °), make the n of AOTF in a spectral range driving frequency f respectively ₁, f ₂, f ₃... f _nlower work, for each driving frequency f _nunder, parallel polychromatic light by AOTF diffraction, and is obtained the diffraction wavelength λ (f under different incidence angles α by high resolution spectrometer _n, α), to α and λ (f _n, α) and carry out least square fitting, and require that quafric curve must be crossed [α=0, λ ₀(f _n)] point, obtain the A in (1) formula after matching _n, see the following form 1:

Table 1 different diffraction light wavelength lambda ₀a value corresponding to (f)

Diffraction wavelength λ 0(f)/nm	617.41	600.88	585.62	571.10	557.59	545.10	533.37
								A	0.1890	0.1774	0.1634	0.1522	0.1481	0.1319	0.1198

Wherein, due to the A under different driving frequency _ndifference, but can approximate representation be:

A _n＝Bλ ₀(f _n)+C(2)

(2) B and C in formula can by the n obtained above (λ ₀(f ₁), A ₁), (λ ₀(f ₂), A ₂), (λ ₀(f ₃), A ₃) ... (λ ₀(f _n), A _n) adopt least square fitting to obtain, after matching, (2) are: A=0.000802 λ ₀(f)-0.3048.

Wherein, in conjunction with (1) formula and (2) Shi Ke get:

λ(f,α)＝[0.000802λ ₀(f)-0.3048]α ²+λ ₀(f)(3)

Wherein, vertical incidence value (i.e. current AOTF generally adopt numerical value), actual measured value and modified value driving frequency be the result of 116MHz, 120MHz, 136MHz and 140MHz respectively as shown in Figure 4, Figure 5, Figure 6 and Figure 7.

Wherein, after matching correction with not have to revise after the relative error of (i.e. current AOTF generally adopt value) contrast as shown in table 2, revised relative error compare revise before to reduce an order of magnitude.

Relative error magnitudes before and after revising under table 2 different diffraction optical wavelength

Wherein, composition graphs 2 and Fig. 3 known, the picture dot x in the x direction of CCD7 _iwith the pass of the focal length F of incident angle α and imaging len 6 be:

$\mathrm{\α}=arctan\left(\frac{il}{F}\right)---\left(4\right)$

L is the length of side of CCD picture dot, and i Wei Yi CCD center is 0 at diffraction direction (i.e. x direction) picture dot x _isequence number.

By (4) formula, (3) formula of bringing into just can obtain the picture dot x in any driving frequency f, arbitrarily the x direction of CCD _ithe centre wavelength of corresponding A OTF diffraction:

$\mathrm{\λ}(f,x_i)=\[0.000802{\mathrm{\λ}}_0\left(f\right)-0.3048\]{\arctan }^2\left(\frac{il}{F}\right)+{\mathrm{\λ}}_0\left(f\right)---\left(5\right).$

Claims (4)

1. the solution that in AOTF same width figure, spectrum is uneven, is characterized in that:

In the spectral range and angular range of AOTF, under any driving frequency f, in incident angle α and this situation, diffraction central wavelength lambda (f, α) can be approximately parabolic relation, is specially:

λ(f,α)＝Aα ²+λ ₀(f)(1)

In above formula, AOTF diffraction light centre wavelength when λ (f, α) is driving frequency is f, incident angle is α; λ ₀f () is driving frequency diffraction light centre wavelength when being f, vertical incidence AOTF; Described λ ₀f (), for carrying when AOTF dispatches from the factory, also can adopt polychromatic light vertical incidence AOTF and be recorded by high resolution spectrometer; Described A adopts following steps to obtain:

AOTF is placed on high-accuracy angle measurement unit and makes the n of AOTF in a spectral range driving frequency f respectively ₁, f ₂, f ₃... f _nlower work, for each driving frequency f _nunder, parallel polychromatic light by AOTF diffraction, and is obtained the diffraction wavelength λ (f under different incidence angles α by high resolution spectrometer _n, α), to α and λ (f _n, α) and carry out least square fitting, and require that quafric curve must be crossed [α=0, λ ₀(f _n)] point, the A obtained after matching _n, A _nfor A in (1) formula, can approximate representation be:

A _n＝Bλ ₀(f _n)+C(2)

B and C in above-mentioned (2) formula can by the n obtained above (λ ₀(f ₁), A ₁), (λ ₀(f ₂), A ₂), (λ ₀(f ₃), A ₃) ... (λ ₀(f _n), A _n) adopt least square fitting to obtain, in conjunction with above-mentioned (1) formula and (2) Shi Ke get:

λ(f,α)＝[Bλ ₀(f)+C]α ²+λ ₀(f)(3)

Because CCD is placed in the focus of imaging len, so the picture dot x of CCD _iwith the pass of the focal length F of incident angle α and imaging len be:

$\mathrm{\α}=arctan\left(\frac{il}{F}\right)---\left(4\right)$

In above formula, l is the length of side of CCD picture dot; I Wei Yi CCD center is 0 at diffraction direction picture dot x _isequence number;

In λ (f, α), λ is the function about f and α, λ (f, x _i) in λ be relevant f and picture dot x _ithe function of sequence number i, therefore can obtain the picture dot x of any driving frequency f, arbitrarily CCD by above-mentioned (4) formula (3) formula of bringing into _ithe centre wavelength of corresponding A OTF diffraction:

$\mathrm{\λ}(f,x_i)=\[{\mathrm{B\λ}}_0\left(f\right)+C\]{\arctan }^2\left(\frac{il}{F}\right)+{\mathrm{\λ}}_0\left(f\right)---\left(5\right).$

2. the solution that in a kind of AOTF according to claim 1 same width figure, spectrum is uneven, is characterized in that: described high-accuracy angle measurement unit is spectroscope, described spectroscope angle-measurement accuracy 1'=0.0167 °.

3. the solving device that in an AOTF same width figure, spectrum is uneven, it is characterized in that: comprise preposition optical system (1), first polaroid (2), diaphragm (3), AOTF (4), second polaroid (5), imaging len (6), CCD (7) and computing machine (8), described preposition optical system (1) is by the first lens (9), second lens (10) and the 3rd lens (11) composition, described first lens (9), second lens (10), 3rd lens (11), first polaroid (2), diaphragm (3), AOTF (4), second polaroid (5), imaging len (6), CCD (7) and computing machine (8) are arranged in order.

4. the solving device that in a kind of AOTF according to claim 3 same width figure, spectrum is uneven, is characterized in that: the polarization direction of described first polaroid (2) and the second polaroid (5) is orthogonal.