A wavefront detection method for middle and far infrared wave band

Abstract

The application provides a wavefront detection method for a middle and far infrared waveband. The method converts the frequency of incident light by irradiating middle and far infrared laser on specific fluorescent material to excite fluorescence, converts the incident long wavelength optical signal into a short wavelength optical signal by using the characteristics of the fluorescent material, measures the converted short wavelength wavefront information by using a common CMOS detector, and obtains the long wavelength wavefront information of the middle and far infrared waveband through the direct correlation between the wavefront information before conversion and the wavefront information after conversion, that is, the long wavelength waveband wavefront information can be detected by using the common CMOS detector, and a specific infrared waveband detector is not needed. The application relates to a method which can detect the middle and far infrared waveband wavefront by using a common Shack-Hartmann wavefront detector. Compared with a wavefront sensor specially used for a long waveband, the long wavelength wavefront information can be directly detected by adding the fluorescent material on the transmission light path.

Description

Technical Field

[0001] This invention relates to the field of wavefront detection technology, specifically to a wavefront detection method for the mid- and far-infrared bands, which can detect infrared wavefront information using ordinary visible light wavefront detectors. Background Technology

[0002] In recent years, adaptive optics technology has undergone continuous development and transformation, creating a surge of interest in its application within the astronomical community. A crucial aspect of adaptive optics is the detection of wavefront information. Advances in stochastic techniques have expanded the detection range beyond the visible light band, with some progress made in infrared detection. However, current wavefront detection technology for the infrared band has only seen limited development. In the near-infrared (NIR) band, InGaAs cameras are commonly used for detection. However, commercially available InGaAs cameras are generally expensive, and their detection range only covers a small portion of the NIR spectrum. Another approach is to use a mercury cadmium telluride (MCT) camera as the detector, but this requires custom-made cameras, is also expensive, and is not yet widely used. Furthermore, the resolution of both detection methods is relatively low compared to visible light detectors. Therefore, this invention proposes utilizing the multiphoton absorption effect of fluorescent materials to convert infrared wavefront information into visible light information, enabling the detection of mid-to-far-infrared wavefront information using a standard CMOS camera.

[0003] As stated above, there is currently a lack of accurate and cost-effective detection methods for wavefront information in the infrared band. This invention addresses this problem by proposing a frequency up-conversion of infrared wavefront information using the multiphoton absorption effect in organic molecules, transforming long-wavelength information into short-wavelength information. This enables the detection of infrared information using ordinary wavefront detectors. This invention also relates to a method that can expand the detection spectrum and reduce detection costs. Summary of the Invention

[0004] The technical problem this invention aims to solve is that current wavefront detection methods are limited by the wavelength range of the detector's response. While ordinary CMOS detectors can accurately detect visible light, detecting wavefront information in the infrared band is more difficult. In the near-infrared (NIR) band, the commonly used approach is to use cameras specifically designed for NIR light, such as InGaAs and cadmium mercury telluride (MCT) cameras. However, these cameras are expensive and their detection range only covers a small portion of the NIR band, resulting in low cost-effectiveness and limited adoption. Therefore, finding a cost-effective and highly accurate method to detect infrared wavefront information has become a significant technical challenge.

[0005] The technical solution adopted by the present invention to solve its technical problem is: by utilizing the characteristics of some organic materials to convert the wavefront information of mid-infrared lasers in terms of frequency, the wavefront information of the infrared band can be converted into the wavefront information of the visible light band, thereby realizing the accurate detection of the wavefront information of the infrared band.

[0006] The specific technical solution is as follows:

[0007] A wavefront detection method for the mid- and far-infrared band, the method comprising the following steps:

[0008] Step (1): A long-wavelength light beam is generated by a laser. The light beam is split and focused into several laser beams after passing through a microlens array. The light beams irradiate the surface of the fluorescent material. After being irradiated by a high-power laser, the fluorescent material produces a nonlinear optical effect, resulting in multiphoton absorption and emission of fluorescence in the visible light band. The light beam completes a frequency conversion. The light beams, after being split and focused by the microlens array, will excite a light spot array pattern on the surface of the fluorescent material. The sub-apertures after the splitting satisfy that the number of pixels in a single sub-aperture is an even number.

[0009] Step (2): Fluorescence is detected by a CMOS detector, and short-wavelength wavefront information is obtained by direct slope method or mode method; the spot array pattern corresponds to the resolution of the CMOS detector.

[0010] Step (3): Based on the excited and displayed light spot array diagram and the segmented sub-aperture, obtain wavefront-related information related to the long wavelength and short wavelength, convert the wavefront-related information according to the frequency, and then use the mode method to restore the long wavelength wavefront information.

[0011] This wavefront detection method breaks through the spectral range detectable by conventional wavefront detectors, extending the detection range to the mid- and far-infrared light band. It uses only a common CMOS detector and utilizes the multiphoton absorption effect of fluorescence to excite fluorescence in the visible light band, converting the detection of mid- and far-infrared laser into the detection of visible light band light signals.

[0012] Furthermore, the fluorescent material described in step (1) can be of any shape or in any state; the cross-sectional size of the fluorescent material is larger than the size of the microlens array, and the fluorescent material is placed in front of the detector.

[0013] Furthermore, the arbitrary shape includes circles and squares; the arbitrary state includes solids and liquids.

[0014] Furthermore, the method for converting wavefront-related information in step (3) is to use the pattern method for fitting to obtain the functional relationship between the wavefront before and after conversion, so that long-wavelength wavefront information can be obtained from short-wavelength wavefront information.

[0015] Furthermore, the number of pixels within a single sub-aperture is 32x32; the wavefront-related information is the centroid position of each sub-aperture spot.

[0016] The principle of this invention is that the multiphoton absorption effect of organic materials can cause frequency upconversion of incident light, thereby stimulating the emission of short-wavelength fluorescence. Based on this principle, this invention proposes a method for generating short-wavelength fluorescence through multiphoton absorption of fluorescent materials, transforming the wavefront detection problem in the infrared band into a wavefront detection problem in the visible light band.

[0017] Compared with existing technologies, this invention excites fluorescence by irradiating a specific fluorescent material with mid-to-far-infrared laser light. This allows for frequency conversion of the incident light using the properties of the fluorescent material, transforming a long-wavelength incident light signal into a short-wavelength light signal. A common CMOS detector is then used to measure the converted short-wavelength wavefront information. By establishing a direct correlation between the wavefront information before and after conversion, the long-wavelength wavefront information in the mid-to-far-infrared band can be obtained. This invention achieves the detection of infrared band information using a common wavefront detector. The method of this invention can expand the detection spectrum and reduce detection costs. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the wavefront transmission optical path structure involved in the present invention;

[0019] Figure 2 This is a schematic diagram illustrating the correlation of wavefront phase information involved in the present invention;

[0020] Figure 3 This is a schematic diagram of the array light spots before and after conversion, as per the present invention. Detailed Implementation

[0021] like Figure 1 As shown, the specific implementation steps of the wavefront detection method for the mid- and far-infrared band of the present invention are as follows:

[0022] Step (1): A long-wavelength light beam is generated by a laser. The light beam is split and focused into several laser beams after passing through a microlens array. The several laser beams irradiate the surface of the fluorescent material. After being irradiated by a high-power laser, the fluorescent material produces a nonlinear optical effect, resulting in multiphoton absorption and emission of visible light fluorescence. The light beam completes a frequency conversion. After being split and focused by the microlens array, the light beam will excite a light spot array pattern on the surface of the fluorescent material. The sub-apertures after the split satisfy that the number of pixels in a single sub-aperture is an even number.

[0023] Fluorescent materials can take any shape, such as circular or square. They can also be in any state, such as solid or liquid. The cross-sectional size of the fluorescent material is larger than the size of the microlens array.

[0024] Step (2): Fluorescence is detected by a CMOS detector, and short-wavelength wavefront information is obtained by direct slope method or mode method; the spot array pattern corresponds to the resolution of the CMOS detector.

[0025] like Figure 3 By obtaining the detected light spot array pattern, the centroid position of each sub-aperture light spot is obtained, thus acquiring wavefront information. If the intensity distribution of the sub-region on the photodetector corresponding to the i-th sub-aperture is I... i (x, y), then the coordinates of the centroid of the far-field spot corresponding to the i-th sub-aperture are:

[0026]

[0027] In the above formula, λ is the wavelength of the beam to be measured, f is the focal length of the microlens, S is the sub-aperture area, and X... l Y l It is the coordinate of the l-th pixel, (X) c (i), Y c (i) represents the centroid coordinates of the light spot corresponding to the i-th sub-aperture. That is, the wavefront slopes (G) in the x and y directions within the i-th sub-aperture. x (i), G y (i) can be represented as:

[0028]

[0029] Taking the mode method as an example, assuming the wavefront phase distribution of the beam under test is φ(x, y), it is expanded using the first n Zernike modes:

[0030]

[0031] Where a k For the k-th Zernike mode Z k The mode coefficients are used to deduce the mode coefficients of the wavefront. Therefore, the essence of wavefront reconstruction using the mode method is to deduce the mode coefficients of the wavefront from the mathematical relationship between the measured average slope of the sub-aperture wavefront and the mode coefficients, thereby obtaining the wavefront to be measured. The relationship between the average slope of the i-th sub-aperture and the Zernike mode coefficients in the Hartmann sensor is as follows:

[0032]

[0033] Among them G x (i), G y (i) represents the average slopes of the i-th sub-aperture wavefront in the x and y directions, respectively, and Z represents the average slopes of the wavefront in the ith direction. xk (i), Z yk(i) represents the average slope of the k-th Zernike mode at the i-th sub-aperture. If the Hartmann sensor has m effective sub-apertures, then the mode recovery can be expressed as:

[0034]

[0035] The above formula can be simplified as follows:

[0036] G = Z·a

[0037] Where G represents the wavefront slope vector calculated from the centroid offset of the light spot, Z is the reconstruction matrix for mode reconstruction, which can be obtained by regional integration of the first-order partial derivative of the Zernike polynomial according to the spatial arrangement of the Hartmann sensor sub-apertures, and a is the coefficient vector of the mode to be measured. During wavefront measurement, the slope vector G can be obtained by measuring the position offset of the centroid of the sub-aperture light spot, and the generalized inverse matrix Zreconstruction matrix can be obtained using singular value decomposition. + Then the least squares solution for the mode coefficient vector a can be obtained:

[0038] a = Z + ·G

[0039] After obtaining the mode coefficient vector 'a', the wavefront to be measured can be obtained by using a linear combination of Zernike polynomials. The results are shown below. Figure 2 .

[0040] Wavefront detectors can use CMOS detectors to detect wavefront information or CCD detectors to detect it.

[0041] Step (3): Based on the excited and displayed spot array diagram and the segmented sub-apertures, obtain wavefront-related information associated with the long and short wavelengths, convert the wavefront-related information according to the frequency, and then use the mode method to restore the long-wavelength wavefront information. The method for converting the wavefront-related information is to use the mode method for fitting to obtain the functional relationship of the wavefront before and after conversion, so that the long-wavelength wavefront information can be obtained from the short-wavelength wavefront information. The specific functional relationship is explained in the same way as in step (2). Through the mode method, the least squares solution of the mode coefficients is obtained, thereby realizing the acquisition of long-wavelength information from short-wavelength information.

[0042] The principle of this invention is that the multiphoton absorption effect of organic materials can cause frequency upconversion of incident light, thereby stimulating the emission of short-wavelength fluorescence. Based on this principle, this invention proposes a method for generating short-wavelength fluorescence through multiphoton absorption of fluorescent materials, transforming the wavefront detection problem in the infrared band into a wavefront detection problem in the visible light band.

[0043] The contents not described in detail in this specification are existing technologies known to those skilled in the art.

Claims

1. A wavefront detection method for the mid- and far-infrared band, characterized in that, The method includes the following steps: Step (1): A long-wavelength light beam is generated by a laser. The beam passes through a microlens array and is split and focused into several laser beams. The several laser beams irradiate the surface of a fluorescent material. The fluorescent material is an organic fluorescent material based on the multiphoton absorption effect, used to upconvert the frequency of the incident mid- and far-infrared light. After being irradiated by a high-power laser, the fluorescent material produces a nonlinear optical effect, resulting in multiphoton absorption and emission of visible light fluorescence, thereby upconverting the frequency of the long-wavelength light beam into short-wavelength fluorescence. The beam, after being split and focused by the microlens array, will excite a light spot array pattern on the surface of the fluorescent material, and the sub-apertures after splitting satisfy an even number configuration of 32×32 pixels within a single sub-aperture. Step (2): Fluorescence is detected by a CMOS detector, and short-wavelength wavefront information is obtained by direct slope method or mode method; the spot array pattern corresponds to the resolution of the CMOS detector. Step (3): Based on the excited and displayed light spot array diagram and the segmented sub-apertures, obtain the wavefront-related information associated with the long wavelength and short wavelength, and use the mode method to fit it to obtain the functional relationship of the wavefront before and after the conversion. Thus, the long wavelength wavefront information can be obtained through the short wavelength wavefront information. The wavefront-related information is the centroid position of each sub-aperture light spot.

2. The wavefront detection method for the mid- and far-infrared band according to claim 1, characterized in that: The fluorescent material described in step (1) can be of any shape or in any state; the cross-sectional size of the fluorescent material is larger than the size of the microlens array, and the fluorescent material is placed in front of the detector.

3. The wavefront detection method for the mid- and far-infrared band according to claim 2, characterized in that: The arbitrary shape includes circles and squares; the arbitrary state includes solids and liquids.

Images