CN110501826B - Method for improving light beam quality based on phase carrier - Google Patents
Method for improving light beam quality based on phase carrier Download PDFInfo
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- CN110501826B CN110501826B CN201810482946.4A CN201810482946A CN110501826B CN 110501826 B CN110501826 B CN 110501826B CN 201810482946 A CN201810482946 A CN 201810482946A CN 110501826 B CN110501826 B CN 110501826B
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
- G02F1/13306—Circuit arrangements or driving methods for the control of single liquid crystal cells
Abstract
A method for improving near-field light beam quality based on phase carrier only needs to set a reflection type phase type spatial light modulator in a light path and load a rectangular phase carrier with proper spatial frequency on the reflection type phase type spatial light modulator, so that the problem of contradiction between the size of a blocked hole in a spatial filter and the size of a filter can be solved, the filtering effect is ensured, and the near-field light beam quality is improved. The invention has the characteristics of simple structure and convenient operation.
Description
Technical Field
The invention relates to the technical field of laser, in particular to a method for improving near-field light beam quality based on a phase carrier.
Background
In a high-power laser system, in the transmission process of a light beam of hundreds of meters, various amplitude modulation and phase modulation can be introduced into a near-field light beam due to the quality of an optical element, dust in the environment, pollution particles and the like, so that the quality of the light beam of the system is reduced, the probability of damage to the optical element is increased, and the operation and maintenance cost of the system is also increased. These modulations are mainly classified into three types, modulation caused by a single local mask, non-periodic random distribution modulation, and periodic modulation. Wherein the periodic modulation introduces side lobes to the far field, which correspond to the spatial frequency of the periodic modulation, in addition to the periodic modulation to the near field. Under a high-flux operation environment, when the nonlinear effect of a medium is considered, the spatial frequency of certain periodic modulation can be subjected to nonlinear rapid growth, a small-scale self-focusing phenomenon is caused, and damage to a subsequent optical element can be excited. The spatial filter is the most commonly used method for filtering out periodic modulation, and its structural diagram is shown in fig. 1, and it is composed of two lenses and a filtering aperture. However, in a high-power laser system, in order to obtain a better filtering effect, the radius of a set filtering aperture is usually very small, and when the filtering aperture is too small, besides introducing a low-frequency diffraction ring to an output near field, a side lobe of periodic modulation and an aperture edge material are easily caused to act at a focal plane to generate a hole blocking problem, which is an important factor influencing the improvement of the load capacity of a high-power laser. The size of the small filtering hole is increased, so that the problem of hole blocking can be avoided to a certain extent, the requirement of filtering is reduced, and an ideal filtering effect cannot be achieved. In 2004 Bagnoud V and Zuegel J D [ see Bagnoud V, Zuegel J D. independent phase and amplitude control of a laser beam by use of a single-phase-only light modulator [ J ]. Optics letters,2004,29(3):295-297] proposed the use of a rectangular phase carrier method to control the amplitude and phase of a near-field beam, thereby shaping the beam. However, the last loaded rectangular phase carrier distribution requires the superposition of two one-dimensional rectangular phase carriers of different spatial frequencies and does not take into account the periodically modulated light beam.
Disclosure of Invention
The invention aims to provide a method for improving the quality of a near-field light beam based on a phase carrier, which only needs to arrange a reflection type phase spatial light modulator in a light path and load a rectangular phase carrier with spatial frequency on the reflection type phase spatial light modulator, so that the problem of the contradiction between the size of a blocked hole in a spatial filter and the size of a filter is solved, the filtering effect is ensured, and the quality of the near-field light beam is improved.
In order to achieve the above object, the technical solution of the present invention is as follows:
a method for improving beam quality based on a phase carrier, the method comprising the steps of:
1) the spatial filter is composed of a first lens, a filtering aperture and a second lens, a first reflector, a second reflector, a polaroid and a beam splitter prism are sequentially arranged in a light path of a periodic modulation light beam in front of the spatial filter, the beam splitter prism divides incident light into transmitted light and reflected light, a detector is arranged in the direction of the reflected light, a reflective phase type spatial light modulator is arranged in the direction of the transmitted light, the beam splitter prism, a third reflector and the spatial filter are sequentially arranged in the direction of the reflected light of the reflective phase type spatial light modulator, the output end of the detector is connected with the input end of a computer, the output end of the computer is connected with the control end of the reflective phase type spatial light modulator, so that the polarization direction of the polaroid is consistent with the long axis direction of a liquid crystal panel of the reflective phase type spatial light modulator, the reflective phase type spatial light modulator is positioned on the front focal plane of the first lens, and the distance from the beam splitter prism to the detector is equal to the distance from the beam splitter prism to the reflective phase type spatial light modulator;
2) the detector detects the light intensity distribution and phase distribution of the light beam, i.e. the light intensity distribution I of the incident light beam at the reflective phase type spatial light modulator0(x0,y0) And phase distribution
And inputting the data into the computer;
3) the computer simulates an ideal Gaussian beam according to the light intensity distribution of the incident beam to serve as the light intensity distribution I of the target beamt(x0,y0) The target wavefront is free of aberrations;
4) according to the light intensity distribution I of the incident beam at the reflective phase type spatial light modulator0(x0,y0) Phase distribution
And the light intensity distribution I of the target beamt(x0,y0) Determining the lower bound of the phase amplitude of the rectangular phase carrier
And upper limit of
The variation with position is:
the phase distribution of the rectangular phase carrier is then represented by:
in the formula, T is the period of the rectangular phase carrier, and n is the number of periods contained in the total width of the rectangular phase carrier;
5) the computer converts the phase distribution of the rectangular phase carrier into a corresponding gray scale map and loads the gray scale map onto the reflective phase type spatial light modulator;
6) after the periodic modulation light beam is processed by the structure, the output light with high light beam quality is output from the spatial filter.
Since the distance from the beam splitter prism to the detector is equal to the distance from the beam splitter prism to the reflective phase-type spatial light modulator, the intensity distribution and the phase distribution of the light beam detected by the detector are the intensity distribution and the phase distribution of the light beam in the near field at the reflective phase-type spatial light modulator.
And the computer converts the phase distribution of the rectangular phase carrier into a corresponding gray-scale image, loads the gray-scale image onto the reflective phase type spatial light modulator, and filters high-order light which is diffracted after passing through the reflective phase type spatial light modulator by using a filtering small hole.
Compared with the prior art, the invention has the beneficial effects that:
according to the invention, a rectangular phase carrier is added on the front focal plane of the first lens of the spatial filter, and when the spatial periodic modulation cannot be effectively filtered by a small filtering hole, effective filtering is realized on the near-field light beam, so that the light beam quality of the near-field light beam is improved;
in a high-power laser system, when the filtering small hole is not blocked and a low-frequency diffraction ring introduced to an output near field cannot be set too small, the filtering effect is reduced, the filtering effect can be improved by using the method provided by the invention, and the problem of the contradiction between the blocking size of the filtering small hole and the filtering size is solved;
in short, the invention can solve the contradiction between the size of the hole blockage in the spatial filter and the filtering size, ensure the filtering effect and improve the near-field light beam quality only by arranging the reflection type phase type spatial light modulator in the light path and loading a rectangular phase carrier wave with proper spatial frequency on the reflection type phase type spatial light modulator. The invention has the characteristics of simple structure and convenient operation.
Drawings
Fig. 1 is a schematic structural diagram of a conventional spatial filter;
FIG. 2 is a schematic structural diagram of a method for improving beam quality based on a phase carrier according to the present invention;
FIG. 3 is a diagram of a phase carrier based beam quality enhancement measurement apparatus of the present invention;
fig. 4 is a one-dimensional average power spectral density curve diagram corresponding to the laser near-field optical beam before and after the phase carrier is loaded in the embodiment of the present invention, where (a) the phase carrier wave is loaded before and (b) the phase carrier wave is loaded after.
Detailed Description
The invention is further illustrated with reference to the following figures and examples, which in turn should not be construed as limiting the scope of the invention.
Referring to fig. 2, fig. 2 is a schematic structural diagram of a method for improving beam quality based on a phase carrier according to the present invention, and it can be seen from the diagram that the method for improving beam quality based on a phase carrier according to the present invention includes the following steps:
1) the spatial filter is composed of a first lens 2, a filtering aperture 3 and a second lens 4, a first reflector 6, a second reflector 7, a polarizer 8 and a beam splitter prism 9 are sequentially arranged in the light path of the periodic modulation light beam 1 in front of the spatial filter, the beam splitter prism 9 splits incident light into transmitted light and reflected light, a detector 10 is arranged in the direction of the reflected light, a reflective phase type spatial light modulator 11 is arranged in the direction of the transmitted light, the beam splitter prism 9, a third reflector 12 and the spatial filter are sequentially arranged in the direction of the reflected light of the reflective phase type spatial light modulator 11, the output end of the detector 10 is connected with the input end of a computer 13, the output end of the computer 13 is connected with the control end of the reflective phase type spatial light modulator 11, so that the polarization direction of the polarizer 8 and the long axis direction of the liquid crystal panel of the reflective phase type spatial light modulator 11 are connected The reflective phase type spatial light modulator 11 is positioned on the front focal plane of the first lens 2, and the distance from the beam splitter prism 9 to the detector 10 is equal to the distance from the beam splitter prism 9 to the reflective phase type spatial light modulator 11;
2) the detector 10 is used to detect the light intensity distribution and phase distribution of the light beam, i.e. the light intensity distribution I of the incident light beam at the reflective phase type spatial light modulator 110(x0,y0) And phase distribution
And input into said computer 13;
3) the computer 13 fits an ideal Gaussian beam according to the light intensity distribution of the incident beam as the light intensity distribution I of the target beamt(x0,y0) The target wavefront is free of aberrations;
4) according to the light intensity distribution I of the incident light beam at the reflective phase type spatial light modulator 110(x0,y0) Phase distribution
And the light intensity distribution I of the target beamt(x0,y0) Determining the lower bound of the phase amplitude of the rectangular phase carrier
And upper limit of
The variation with position is:
the phase distribution of the rectangular phase carrier is then represented by:
in the formula, T is the period of the rectangular phase carrier, and n is the number of periods contained in the total width of the rectangular phase carrier;
5) the computer 13 converts the phase distribution of the rectangular phase carrier into a corresponding gray scale map, and loads the gray scale map onto the reflective phase type spatial light modulator 11;
6) after the periodic modulation light beam 1 is subjected to the structure and the processing, the output light with high beam quality is output from the spatial filter.
FIG. 3 is a diagram of an embodiment of the method and the measuring device thereof of the present invention, in which a CCD14 is placed at the back focal plane of the second lens 4 for detecting the intensity distribution of the emergent light beam, in this embodiment, the amplitude modulation degree of the periodically modulated light beam 1 is 0.1, and the spatial frequency is 12mm-1The cut-off frequency of the filter aperture 3 in the spatial filter is 13.35mm-1It cannot transmit 12mm of light beam-1The focal lengths of the first lens 2 and the second lens 4 are both 17.5cm, and the beam splitter prism 9 is 5: 5, a common non-polarization beam splitter prism, a reflective phase type spatial light modulator 11 adopts a pure phase spatial light modulator with the model of LETO and 1920 multiplied by 1080 pixels, and a photoelectric coupling detector CCD14 adopts a black and white CCD with large and constant DH-SV1411GM and 1392 multiplied by 1040 pixels;
2) detecting the light intensity distribution and the phase distribution of the light beams by using a detector, namely the light intensity distribution and the phase distribution of the incident light beams at the position of the reflective phase type spatial light modulator;
3) fitting an ideal Gaussian beam according to the light intensity distribution of the incident beam by using a computer to serve as the light intensity distribution of the target beam, wherein the target wavefront does not contain aberration;
4) according to the light intensity distribution I of the incident beam at the reflective phase type spatial light modulator0(x0,y0) Phase distribution
And the light intensity distribution I of the target beamt(x0,y0) Determining a lower bound for the phase amplitude of the rectangular phase carrier
And upper limit of
The variation with position is:
the phase distribution of the rectangular phase carrier can be represented by:
where T is the period of the rectangular phase carrier, and n is the number of periods included in the total width of the rectangular phase carrier, in this embodiment, the period T of the rectangular phase carrier is set to 2 reflective phase type spatial light modulator pixels, and the number of n is 960.
5) The reflective phase type spatial light modulator 11 controls the electrode voltage by using the gray scale data of the gray scale image drawn by the computer 13, thereby controlling the change of the light beam phase by the single liquid crystal pixelThe phase and gray scale data are linearly related (see: Xugui quan, Von Shatong, Nie Saiping, et al. phase modulation characteristics test of reflective spatial light modulators [ J ]]The laser technology, 2009,33(6):571-, as can be seen from comparison with FIG. 4(b), the spatial frequency is 12.4mm-1The intensity drops by an order of magnitude and to near the background value.
Experiments show that the problem of the contradiction between the size of a blocked hole in a spatial filter and the size of a filter can be solved, the filtering effect is ensured, and the near-field light beam quality is improved only by arranging the reflective phase type spatial light modulator in a light path and loading a rectangular phase carrier wave with proper spatial frequency on the reflective phase type spatial light modulator. The invention has the characteristics of simple structure and convenient operation.
The foregoing is only an embodiment of the present invention, and it should be noted that those skilled in the art can make any modification, replacement or improvement without departing from the principle and implementation of the present invention, and the modification, replacement or improvement is included in the protection scope of the present invention.
Claims (1)
1. A method for improving beam quality based on a phase carrier, the method comprising the steps of:
1) the spatial filter consists of a first lens (2), a filtering pinhole (3) and a second lens (4), a first reflecting mirror (6), a second reflecting mirror (7), a polarizing plate (8) and a light splitting prism (9) are sequentially arranged in a light path of a periodic modulation light beam (1) in front of the spatial filter, the light splitting prism (9) divides incident light into transmission light and reflection light, a detector (10) is arranged in the direction of the reflection light, a reflection phase type spatial light modulator (11) is arranged in the direction of the transmission light, the light splitting prism (9), a third reflecting mirror (12) and the spatial filter are sequentially arranged in the direction of the reflection light of the reflection phase type spatial light modulator (11), the output end of the detector (10) is connected with the input end of a computer (13), the output end of the computer (13) is connected with the control end of the reflection phase type spatial light modulator (11), the polarization direction of the polarizer (8) is consistent with the long axis direction of the liquid crystal panel of the reflective phase type spatial light modulator (11), the reflective phase type spatial light modulator (11) is positioned on the front focal plane of the first lens (2), and the distance from the beam splitter prism (9) to the detector (10) is equal to the distance from the beam splitter prism (9) to the reflective phase type spatial light modulator (11);
2) the detector (10) is used for detecting the light intensity distribution and the phase distribution of the light beam, namely the light intensity distribution I of the incident light beam at the position of the reflective phase type spatial light modulator (11)0(x0,y0) And phase distribution
And input into said computer (13);
3) the computer (13) fits an ideal Gaussian beam according to the light intensity distribution of the incident beam to be used as the light intensity distribution I of the target beamt(x0,y0) The target wavefront is free of aberrations;
4) according to the light intensity distribution I of the incident light beam at the reflective phase type spatial light modulator (11)0(x0,y0) Phase distribution
And the light intensity distribution I of the target beamt(x0,y0) Determining the lower bound of the phase amplitude of the rectangular phase carrier
And upper limit of
The variation with position is:
the phase distribution of the rectangular phase carrier is then represented by:
in the formula, T is the period of the rectangular phase carrier, and n is the number of periods contained in the total width of the rectangular phase carrier;
5) the computer (13) converts the phase distribution of the rectangular phase carrier into a corresponding gray scale map and loads the gray scale map onto the reflective phase type spatial light modulator (11);
6) after the periodic modulation light beam (1) is subjected to the structure and the processing, the output light with high beam quality is output from the spatial filter.
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| US8198564B2 (en) * | 2008-09-09 | 2012-06-12 | Electro Scientific Industries, Inc. | Adaptive optic beamshaping in laser processing systems |
| GB2504257A (en) * | 2012-03-20 | 2014-01-29 | Isis Innovation | Adaptive optics for combined pulse front and phase front control |
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| CN103048791A (en) * | 2013-01-18 | 2013-04-17 | 苏州大学 | Method for producing partially coherent Airy beams |
| CN105264428A (en) * | 2013-06-06 | 2016-01-20 | 浜松光子学株式会社 | Adjustment method for adaptive optics system, adaptive optics system, and storage medium storing program for adaptive optics system |
| CN104852269A (en) * | 2015-05-26 | 2015-08-19 | 山西大学 | Device and method for accurately modulating pulse laser phase |
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Non-Patent Citations (3)
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