Spectral radiation brightness measuring and calibrating method of point light source

Abstract

The invention relates to the field of optical metrology testing, and particularly discloses a point light source spectral radiance measuring and calibrating method, which is implemented by the following scheme: a point light source outputs spectral radiance, and a measured light source is imaged on an entrance slit of a double-cascade monochromator through a front optical system; the double-cascade monochromator is driven by the control system to split incident polychromatic light and output monochromatic light, the photoelectric detector receives the monochromatic light and outputs current, and the current is amplified by the high-precision amplifier and then is subjected to data acquisition and processing by the PC upper computer. An integrating sphere which has the same field of view with the point light source and has known spectral radiation brightness is used as a standard light source illumination test system, the absolute spectral responsivity of the whole system is calibrated, and the spectral radiation brightness of the point light source is tested by using the calibrated absolute spectral responsivity of the whole system; according to the invention, measurement of the spectral radiance of a weak point light source in a wide band can be realized.

Description

Technical Field

[0001] The invention belongs to the field of optical metrology and testing, and mainly relates to a spectral radiation measurement and calibration method, and in particular to a spectral radiation brightness measurement and calibration method of a micrometer-level point light source. Background Art

[0002] A point light source is an idealized light wave source. It is assumed to be a point at infinity. The size of the light source can be ignored. The light waves emitted from this point propagate radially, and at an infinite distance from the light source, the light waves can be regarded as parallel light. Point light sources usually have two meanings: one is that the light source is extremely small. When the measured optical path is much larger than the size of the receiving surface and the radiation source (>>10), the radiation source can be regarded as a point source for measurement. The radiation intensity of a point light source is usually expressed in watts / solid angle (W / Sr); the spectral radiance indicates the radiation flux emitted by the light source within a unit solid angle and per unit area, and is the main physical quantity in radiometry to measure the luminous ability of a light source.

[0003] Currently, radiation calibrated radiometers are often used to measure the (spectral) radiance of light sources. However, commonly used spectral radiometers are limited by the measurement field of view and can only meet the radiance measurement requirements of light sources that can fill the field of view of the radiometer and have a large area, such as integrating sphere light sources. For point light sources with a diameter of the order of microns, existing spectral radiometry instruments cannot meet their radiance measurement requirements. Summary of the invention

[0004] In view of the difficulty of high-accuracy measurement of the spectral radiant brightness of a point light source, no relevant research has been found on the measurement of the spectral radiant brightness of a point light source with a diameter of micrometers. The purpose of the present invention is to realize the measurement of the spectral radiant brightness of a point light source based on a point light source, especially when the brightness of the light source in the ultraviolet band is weak. To achieve the above purpose, the present invention provides the following technical solutions: a method for measuring the spectral radiant brightness of a point light source, the point light source outputs the spectral radiant brightness, the measured light source is imaged onto the incident slit of a double cascade monochromator through a front optical system, the double cascade monochromator splits the incident complex light and outputs monochromatic light under the drive of a control system, the photodetector receives the monochromatic light and outputs current, after amplification by a high-precision amplifier, the PC host computer performs data acquisition and processing, the absolute spectral responsivity of the whole system can be calculated, and the spectral radiant brightness of the point light source can be obtained.

[0005] Preferably, the spectral radiance at the entrance slit of the monochromator is calculated and derived based on the geometric relationship between the point light source, the front optical system and the photodetector, and the spectral radiance at the entrance slit of the monochromator is substituted into the radiant light power on the receiving surface of the photodetector according to the radiometry theory. The corresponding output photocurrent of the system light source output radiant brightness is derived through the spectral radiance at the entrance slit of the monochromator, the radiant light power on the receiving surface of the photodetector, and the spectral responsivity of the photodetector, and it is concluded that the output current of the photoelectric system is proportional to the incident radiation brightness and the measurement bandwidth.

[0006] Preferably, a large-area photodetector is used to receive all the optical power output from the monochromator exit slit.

[0007] The above-mentioned system is calibrated, and an integrating sphere with the same field of view and known spectral radiation brightness as the point light source is used as a standard light source illumination test system. The absolute spectral responsivity of the system is calibrated, and the spectral radiation brightness of the point light source is tested using the calibrated absolute spectral responsivity of the system.

[0008] Preferably, the above method for point light source spectral radiation brightness calibration is applied to absolute calibration from ultraviolet to visible band based on different radiation standard lamps: using ultraviolet band spectral radiation brightness standard lamp to test system ultraviolet band spectral radiation brightness response; using standard integrating sphere light source to calibrate visible light band spectral radiation brightness response; after processing the normalized spectral response curves of ultraviolet and visible bands respectively, the two relative spectral distribution curves are fitted by least squares method to obtain a relative spectral curve of 200nm-800nm ​​band, and within the 200nm-800nm ​​band, the absolute spectral radiation brightness response at the visible light peak wavelength in the above relative spectral distribution curve is substituted into the relative spectral distribution curve to obtain the absolute spectral radiation brightness response of the whole band.

[0009] Compared with the prior art, the present invention has the following beneficial effects:

[0010] 1. The present invention realizes the measurement of the spectral radiation brightness of a point light source with a diameter of 100 microns, which not only fills the gap in the point light source spectral radiation testing and calibration technology, but also has the ability to measure point light sources with high precision and high accuracy.

[0011] 2. Aiming at the problem of measuring the spectral radiance of a point light source, the present invention proposes and solves a physical model of spectral radiance transmission based on geometric imaging and radiometry theory.

[0012] 3. The present invention establishes a response function relationship between the spectral radiation brightness of a point light source and the output signal of a measurement system.

[0013] 4. The present invention is a method for calibrating the absolute spectral radiation brightness of a measurement system under weak light conditions of a point light source, and proposes a method for calibrating the absolute spectral radiation brightness in the ultraviolet-visible light band based on different standard radiation light sources.

[0014] 5. The present invention normalizes the spectral response curves of the two bands of the measurement system obtained based on two standard spectral radiation sources respectively, and obtains a full-band relative spectral response curve in combination with the curve connection algorithm, thereby realizing the full-band absolute spectral radiation brightness calibration of the point light source measurement system.

[0015] 6. The point light source spectral radiation brightness measurement and calibration method of the present invention is applicable to the measurement application of wide-band point light sources in the entire ultraviolet to infrared band. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG1 is a block diagram of the principle of a point light source spectral radiance measurement system;

[0017] Figure 2 It is a schematic diagram of the geometric relationship of objects;

[0018] Figure 3 The radiation transmission optical path for measuring the spectral radiation of the light source;

[0019] Figure 4 This is a schematic diagram of the calibration principle of the spectral radiation illumination response in the ultraviolet band;

[0020] Figure 5 Schematic diagram of the calibration principle of spectral radiance responsivity in the visible light band. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0022] like Figure 1 As shown, the point light source spectral radiance measurement principle of the present invention is that the point light source outputs spectral radiance , the measured light source is imaged onto the incident slit of the monochromator M through the front optical system O. The double cascade monochromator splits the incident complex light under the drive of the control system, and the output optical power is The spectral response of monochromatic light is Photodetector D receives monochromatic light and outputs current After being amplified by a high-precision amplifier, the data is collected and processed by a PC host computer.

[0023] Derivation of the radiant light power on the receiving surface of the photodetector based on radiometric theory As shown in formula (3), the derivation process is as follows:

[0024] like Figure 2As shown, the point light source As forms a solid angle of According to the principle of radiometry, the spectral radiance is the product of the spectral radiance emitted by the light source and the solid angle, that is, . Then the point light source outputs spectral radiance With the spectral transmittance The illumination relationship generated by the front optical system at Ao is shown in formula (1):

[0025] (1),

[0026] A point light source with an area of ​​As passes through the optical system O and forms an image spot at the entrance slit of the monochromator. The ratio of the light source area As is inversely proportional to the square of the magnification, that is, S1 2 / S 2 2. Based on this geometric relationship, the spectral radiance at the monochromator entrance slit is derived: (Unit: W / m 2 The expression of μm is shown in formula (2):

[0027] (2),

[0028] Spectral radiance at the entrance slit After being split by the monochromator, the radiant light power at the exit slit is (Unit: W / μm) As shown in formula (3):

[0029] (3),

[0030] in is the incident area of ​​the monochromator, The imaging spot should fill the incident slit by limiting the height and width of the slit, that is, Since the imaging magnification of the bipolar monochromator β=1, the light power incident on the photodetector remains unchanged, and the use of a large-area photodetector can receive all the light power output by the monochromator exit slit.

[0031] The radiance output by this light source According to the optical path in Figure 3 and formulas (2) and (3), as well as the spectral responsivity of the photodetector Derive the system output photocurrent (Unit: A) and the spectral radiation brightness emitted by the measured point light source The relationship is shown in formula (4):

[0032] (4)

[0033] in:

[0034] is the spectral radiance of the light source, in w / m 2 sr μm;

[0035] A O is the area of ​​the front optical system, unit: m 2 ;

[0036] S1 is the entrance pupil distance between the light source and the optical system, unit: m;

[0037] S2 is the diameter of the optical system and monochromator, unit: m;

[0038] is the area of ​​the monochromator entrance slit, unit: m 2 ;

[0039] is the spectral reflectance in the front optical system;

[0040] is the spectral transmittance of the double cascade monochromator system;

[0041] is the dark signal output by the amplifier;

[0042] is the spectral responsivity of the photodetector D, in A / W;

[0043] The full width at half maximum (FWMH) of the spectrum of the monochromator.

[0044] Let the absolute spectral responsivity of the system be :

[0045] (5)

[0046] Formula (6) is derived from formula (5) and formula (4):

[0047] (6)

[0048] Formula 6 shows that the output current of the photoelectric system is related to the incident radiation brightness Proportional to the measurement bandwidth The absolute spectral responsivity of the system is This is achieved through spectral radiometric calibration.

[0049] Point light source spectral radiance calibration method: Use an integrating sphere standard light source illumination test system with the same field of view and known spectral radiance as the point light source to calibrate the absolute spectral responsivity of the entire system .

[0050] (7) In formula (7): is the known spectral radiance output by the integrating sphere standard light source, To measure bandwidth.

[0051] The absolute spectral responsivity of the system after calibration Test the spectral radiance of a point light source.

[0052] Since the energy of the integrating sphere standard light source in the deep ultraviolet band is weak, the uncertainty is large, the signal-to-noise ratio is small during calibration, and the existing technology cannot provide the standard spectral radiation brightness value in this band, an innovative absolute calibration method for the ultraviolet to visible band based on different radiation standard lamps is proposed. This method uses ultraviolet band spectral radiation illumination standard lamps (such as deuterium lamps, xenon lamps, etc.) to test the ultraviolet band spectral radiation illumination response of the system. ; Use standard integrating sphere light source (built-in bromine tungsten lamp) to calibrate the spectral radiation brightness response of the visible light band .

[0053] The calibration principles of ultraviolet band spectral radiance and visible light band spectral radiance brightness are as follows:

[0054] like Figure 4 As shown, the spectral irradiance responsivity in the ultraviolet band Calibration is to place the point spectral radiance lamp at the point light source position, and measure the standard spectral radiance generated at the front optical system O of the system as After passing through the system, the output current is Spectral irradiance The conversion relationship is shown in formula (8). Since the radiation intensity of the standard deuterium lamp or xenon lamp is relatively high in the ultraviolet band of 200nm~420nm, the standard deuterium lamp can be used to calibrate the spectral radiation illumination response with a high signal-to-noise ratio. Then, the absolute spectral irradiance curve is normalized using formula (9) to obtain the dimensionless relative spectral distribution curve: .

[0055] (8)

[0056] (9)

[0057] Represents the standard spectral radiance responsivity ( );

[0058] Represents the absolute spectral radiance responsivity at the peak wavelength ( );

[0059] It represents the peak normalized relative spectral distribution curve in the ultraviolet band of 200nm~420nm.

[0060] like Figure 5 As shown, the spectral radiation brightness response of the visible light band The calibration uses an integrating sphere standard light source to illuminate the front optical system O, and its output standard spectral radiation brightness is , under the illumination of the integrating sphere standard light source, the system output current is , current and spectral radiance The conversion relationship is shown in formula (10). Since the standard integrating sphere light source based on bromine tungsten lamp has a high radiation intensity in the visible light range, the standard lamp can be used to calibrate the spectral radiation brightness response with high signal-to-noise ratio. Then, the absolute spectral radiance response is normalized using formula (11) to obtain the dimensionless relative spectral distribution curve: .

[0061] (10)

[0062] (11)

[0063] Represents the standard spectral radiance responsivity ( );

[0064] Represents the absolute spectral radiance responsivity at the peak wavelength ( );

[0065] It represents the peak normalized relative spectral distribution curve in the ultraviolet band of 400nm~800nm.

[0066] After processing the normalized spectral response curves of the ultraviolet and visible bands respectively, the two relative spectral distribution curves were fitted using the least squares method to obtain a relative spectral curve of the band 200nm-800nm .

[0067] In the 200nm-800nm ​​band, the absolute spectral radiance responsiveness at the peak wavelength of visible light in the above relative spectral distribution curve is Substitute into the relative spectral distribution curve The absolute spectral radiance responsivity of the whole band is obtained :

[0068] (12),

[0069] in: It is the relative spectral response of the entire band from ultraviolet to visible.

Claims

1. A method for measuring and calibrating the spectral radiance of a point light source, characterized in that: The point light source outputs spectral radiation brightness. The measured light source is imaged onto the incident slit of the double cascade monochromator through the front optical system. The double cascade monochromator splits the incident complex light into monochromatic light under the drive of the control system. The photodetector receives the monochromatic light and outputs current. After amplification by a high-precision amplifier, the PC host computer collects and processes the data. The absolute spectral responsivity of the whole system can be calculated to obtain the spectral radiation brightness of the point light source.

2. The method for measuring and calibrating the spectral radiance of a point light source according to claim 1, characterized in that: According to the geometric relationship between the point light source, the front optical system and the photodetector, the spectral radiance at the entrance slit of the monochromator is calculated and derived. The spectral radiance at the entrance slit of the monochromator is substituted into the radiant light power on the receiving surface of the photodetector according to the radiometry theory. The corresponding output photocurrent of the system light source output radiant brightness is derived through the spectral radiance at the entrance slit of the monochromator, the radiant light power on the receiving surface of the photodetector, and the spectral responsivity of the photodetector. It is concluded that the output current of the photoelectric system is proportional to the incident radiation brightness and the measurement bandwidth.

3. The method for measuring and calibrating the spectral radiation brightness of a point light source according to claim 2, characterized in that: A large-area photodetector is used to receive all the optical power output from the monochromator exit slit.

4. The method for measuring and calibrating the spectral radiation brightness of a point light source according to claim 1, characterized in that: The above-mentioned system is calibrated, including the following steps: using an integrating sphere with the same field of view and known spectral radiation brightness as the point light source as a standard light source illumination test system, calibrating the absolute spectral responsivity of the system, and testing the spectral radiation brightness of the point light source using the calibrated absolute spectral responsivity of the system.

5. The method for measuring and calibrating the spectral radiance of a point light source according to claim 4, characterized in that: The above method for point light source spectral radiation brightness calibration is applied to absolute calibration from ultraviolet to visible band based on different radiation standard lamps: the ultraviolet band spectral radiation brightness standard lamp is used to test the ultraviolet band spectral radiation brightness response of the system; the standard integrating sphere light source is used to calibrate the visible light band spectral radiation brightness response; after processing the normalized spectral response curves of the ultraviolet and visible bands respectively, the two relative spectral distribution curves are fitted by the least squares method to obtain a relative spectral curve of the band 200nm-800nm, and within the 200nm-800nm ​​band, the absolute spectral radiation brightness response at the visible light peak wavelength in the above relative spectral distribution curve is substituted into the relative spectral distribution curve to obtain the absolute spectral radiation brightness response of the whole band.

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