CN106908144A - A kind of ultraweak starlight illumination measurement apparatus and method - Google Patents

Abstract

The invention provides an ultra-weak starlight illuminance measurement device and method, the device includes an optical lens, a beam splitter, a measurement channel I, a measurement channel II and a data processor; the optical lens is connected to the beam splitter, the measurement channel I and the measurement channel II is respectively connected between the beam splitter and the data processor; measurement channel I includes photodetector I, preamplifier I and photon counter I; measurement channel II includes monochromator, photodetector II, preamplifier II, Photon Counter II. This device uses two measurement channels to count and measure the number of photons, obtain the total photon count and at the same time obtain the photon number of monochromatic light, and can obtain the proportion of photons of different wavelengths in the total photon count, and the count is accurate at the same time, and does not need to be repeated Measure the light energy spectral distribution in the light beam at the same time, which can improve the accuracy of illuminance measurement, and can realize the measurement of ^10-13 lx ultra-weak starlight illuminance.

Description

An ultra-weak starlight illuminance measurement device and method

technical field

The invention relates to the field of starlight illuminance measurement, in particular to an ultra-weak starlight illuminance measurement device and method with low signal-to-noise ratio and high measurement accuracy.

Background technique

At present, with the development of photoelectric detection technology, higher and higher measurement requirements are put forward for the measurement of weak illuminance in the fields of space target detection, starlight navigation and biomedicine. about 10 ^-3 lx) to magnitude 7 stars (about 10 ^-9 lx), where lx is lux, the international unit of illuminance; the illuminance of space exploration targets is about 10 ^-11 lx; the fluorescence illuminance in the biomedical field is even lower , and the current low-light illuminance meter can only reach 10 ^-3 ~ 10 ^-5 lx, which is far from meeting the low-light illuminance measurement requirements in these frontier fields.

A typical illuminance meter is composed of a cosine corrector, a filter, a detector, and a data processor. It exhibits high measurement repeatability and accuracy in the measurement of strong light illumination, but the signal-to-noise ratio is extremely low in the measurement of ultra-weak starlight. , even the optical signal cannot be captured.

Contents of the invention

The object of the present invention is to provide an ultra-weak starlight illuminance measurement device and method to solve the problem of poor precision of starlight illuminance meter and inability to realize ultra-weak starlight measurement.

Specifically, the present invention provides an ultra-weak starlight illumination measurement device, comprising an optical lens (1), a beam splitter (2), a measurement channel I, a measurement channel II and a data processor (10);

The optical lens (1) is connected to the beam splitter (2), and the measurement channel I and the measurement channel II are respectively connected between the beam splitter (2) and the data processor (10);

The measurement channel I includes a photodetector I (3), a preamplifier I (4) and a photon counter I (5);

The photodetector I (3) is connected with the beam splitter (2), followed by the preamplifier I (4) and the photon counter I (5), and the photon counter I (5) and the data processor (10 ) are connected;

The measurement channel II includes a monochromator (6), a photodetector II (7), a preamplifier II (8), and a photon counter II (9);

The monochromator (6) is connected to the beam splitter (2), and the monochromator (6) is sequentially connected to the photodetector II (7), the preamplifier II (8) and the photon counter II (9), and the photon The counter II (9) is connected with the data processor (10).

Further, the optical lens (1) includes a diaphragm, and the aperture of the aperture is a circular aperture with a diameter D, and the diameter D of the aperture of the aperture is the effective diameter of the optical lens (1).

Further, the effective diameter D of the optical lens (1) is smaller than the exit pupil size D′ of the starlight simulator, and the angle of view 2β is greater than the divergence angle 2α of the incident light beam, so as to ensure that all the incident light enters the range of the optical lens for energy concentration .

Further, the beam splitter (2) has an optical aperture of 20mm×20mm×20mm, is coated with a 50% semi-reflective and semi-transparent film layer, and is coated with a 0.4 μm-0.8 μm optical anti-reflection film on the incident and exit surfaces of the light, and a single surface transmits The efficiency is not lower than 98%. The beam splitter (2) divides the incident light beam into two paths, and reduces the loss of the incident light beam as much as possible, that is, reduces reflected light and increases transmitted light.

Further, the monochromator (6) has a spectral range of 0.4 μm to 0.8 μm, a spectral resolution of 2 nm±1, a wavelength position repeatability of ±1 nm, and an NA value of 0.4. Adjusting the monochromator (6) can obtain Monochromatic light of different wavelengths in different spectral ranges.

In particular, a method for measuring ultra-weak starlight illumination of the measuring device, comprising the following steps:

Step 1. The incident light beam passes through the optical lens (1) to collect the luminous flux, and the incident light beam is divided into two paths through the beam splitter (2);

Step 2. The incident light beam converges on the photosensitive surface of the photodetector I (3) for photoelectric conversion and outputs an electrical signal; the other path enters the monochromator (6) for dispersion and light splitting to obtain a monochromatic light beam with a wavelength of λ. Light;

Step 3: The photodetector Ⅰ (3) amplifies the output electrical signal through the preamplifier Ⅰ (4); then the photon counter Ⅰ (5) counts the photons with high precision, counting the number of photons of the incident light, Get the total number of photon counts;

Step 4: The monochromatic light after dispersion and splitting converges on the photosensitive surface of the photodetector II (7) for photoelectric conversion, converting the optical signal into an electrical signal; the photodetector II (7) passes the output electrical signal through the front Place the amplifier II (8) to amplify; then count the photons through the photon counter II (9) to obtain the number of photons with a wavelength of λ, and measure the light energy spectral distribution in the beam to be measured;

Step 5, adjusting the monochromator (6), then monochromatic light of different wavelengths can be obtained, repeating steps 3 and 4;

Step 6: The measured values of photon counter I (5) and photon counter II (9) are transmitted to the data processor (10) as input data, and the illuminance is obtained by using the mathematical model of ultra-weak starlight illuminance.

Further, the mathematical model of ultra-weak starlight illumination is:

Among them, E—illuminance;

A—absolute spectral efficiency value of monochromatic light (wavelength 507nm) under scotopic conditions;

h—Planck's constant;

c—the speed of light in vacuum;

M—the total amount of photon counts counted by the photon counter I (5);

S—the area of the entrance pupil of the optical lens, which refers to the area of the aperture of the diaphragm, specifically S=(ΠD ² )/4;

η _λ - the visual function of monochromatic light with wavelength λ;

λ—wavelength of incident light;

k _λ —the proportion coefficient of the number of photons with a wavelength of λ in the total photon count.

Further, the k _λ is the ratio of the number of photons with a wavelength λ counted by the photon counter II (9) to the total number of photons counted by the photon counter I (5).

Particularly, the restrictive conditions when measuring device and measuring method of the present invention are used are:

(1) The effective caliber D of the optical lens (1) is smaller than the exit pupil size D′ of the starlight simulator, the angle of view 2β is larger than the divergence angle of the incident light beam by 2α, and the deviation is controlled within the range of ±20%β;

(2) The illuminance of the measured light is uniform on the measured area, and this area covers the entrance pupil area (S) in the ultra-weak starlight illuminance measurement device;

(3) The measured illuminance measurement is a non-transient measurement, that is, the light source can be continuously and stably lit for a long time.

The invention provides an ultra-weak starlight illuminance measurement device and method, which uses two measurement channels to count and measure the photon number, and obtains the photon number of monochromatic light while obtaining the total photon count, and can obtain the difference in the total photon count. The ratio of wavelength photons can be counted accurately at the same time, and there is no need to repeat the measurement. At the same time, the light energy spectral distribution in the beam can be measured, which can improve the measurement accuracy of illuminance, and can realize the measurement of 10 ^-13 lx ultra-weak starlight illuminance.

Description of drawings

The drawings are for the purpose of illustrating specific embodiments only and are not to be considered as limitations of the invention, and like reference numerals refer to like parts throughout the drawings.

Fig. 1 is a schematic diagram of the overall structure of the ultra-weak starlight illuminance measuring device of the present invention.

In the figure: 1-optical lens, 2-beam splitter, 3-photodetector Ⅰ, 4-preamplifier Ⅰ, 5-photon counter Ⅰ, 6-monochromator, 7-photodetector Ⅱ, 8-front Place amplifier Ⅱ, 9-photon counter Ⅱ, 10-data processor.

detailed description

The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

The invention provides a device and method for measuring ultra-weak starlight illumination. Weak starlight refers to starlight with an illuminance within the range of 10 ^-8 to 10 ^-9 lx, and ultra-weak starlight refers to starlight with an illuminance lower than 10 ^-9 lx .

As shown in Fig. 1, the measurement device includes an optical lens (1), a beam splitter (2), a measurement channel I, a measurement channel II and a data processor (10).

The optical lens (1) is connected with the beam splitter (2), and the measurement channel I and the measurement channel II are respectively connected between the beam splitter (2) and the data processor (10).

Measurement channel I includes photodetector I (3), preamplifier I (4) and photon counter I (5).

The photodetector I (3) is connected to the beam splitter (2), followed by the preamplifier I (4) and the photon counter I (5), and the photon counter I (5) is connected to the data processor (10) connect.

The measurement channel II includes a monochromator (6), a photodetector II (7), a preamplifier II (8), and a photon counter II (9).

The monochromator (6) is connected to the beam splitter (2), and the monochromator (6) is sequentially connected to the photodetector II (7), the preamplifier II (8) and the photon counter II (9), and the photon counter II (9) is connected with the data processor (10).

During the measurement, the starlight simulator is used to emit the incident light beam, the diameter of the exit pupil of the starlight simulator is D′, and the divergence angle of the emitted incident light beam is 2α. The optical lens (1) aggregates the energy of the incident light, and the beam splitter (2) splits the incident light. After the beam splitting, one path of the incident light is processed by the measurement channel I to measure the total photon number of the incident light, and the photon count is obtained. total amount; another routing monochromator (6) separates the incident light to obtain the monochromatic light with a wavelength of λ, and counts the number of photons of the monochromatic light with a wavelength of λ in the incident light by the measurement channel II to obtain the wavelength is the photon number of λ.

The effective aperture of the optical lens (1) is 20mm±0.02mm, the effective focal length is 100mm±0.1mm, and the viewing angle 2β is 2°±0.1°, which should be larger than the divergence angle of the incident light beam by 2α. The optical lens (1) adopts a cooker-type three-piece lens, including three lenses. The radius of curvature of the front surface of the first lens is 49.43mm, the thickness is 6.3±0.1mm, the radius of curvature of the rear surface is -352.18mm, and the lens material is SK16. The distance between the front surface of the second lens and the back surface of the first lens is 11.3±0.1mm, the radius of curvature of the front surface of the second lens is -46.86mm, the thickness is 7.2±0.1mm, and the radius of curvature of the back surface is 44.35 mm, the lens material is F2. The distance between the front surface of the third lens and the back surface of the second lens is 7.2±0.1mm, the radius of curvature of the front surface of the third lens is 119.08mm, the thickness is 7.5±0.1mm, the radius of curvature of the back surface is -40.7mm, and the back surface The distance from the focal plane of the optical lens is 83.7±0.1mm, and the optical material is SK16. The diaphragm is located between the second lens and the third lens. The distance between the front surface of the diaphragm and the rear surface of the second lens is 7.2±0.1mm. The aperture of the diaphragm is a circular hole with a diameter of D=20mm. The diameter D of the aperture is the effective aperture of the optical lens (1), which should be smaller than the exit pupil diameter D′ of the starlight simulator. The optical surfaces of the three lenses are all coated with 0.4μm-0.8μm optical anti-reflection film, and the transmittance of a single optical lens is not less than 95%. This lens is conducive to the collection of ultra-weak starlight radiation energy, and it can realize the measurement of ^10-15 lx illuminance with the subsequent photodetector estimation.

The beam splitter (2) is a 45° beam splitting prism, which is composed of two 45° right-angled triangular prisms, with an optical glue layer in the middle. The optical aperture is 20mm×20mm×20mm, the angle between the middle optical bonding layer and the incident light is 45°±0.1°, coated with 50% semi-reflective and semi-transparent film layer, and coated with 0.4μm～0.8μm optical anti-reflection film on the light incident and exit surfaces , The transmittance of the lens is not less than 98%. The optical material of the beam splitter is fused silica optical glass.

The photodetector Ⅰ (3) adopts the R2949 photomultiplier tube of Japan Hamamatsu Company, cooperates with the electric refrigerator C9144, the dark count rate is less than 15photons/s, the side window opening is 6mm×6mm, and the front end is equipped with a visual function _ηλ filter The chip can remove the spectrum other than 0.4μm ~ 0.8μm.

Preamplifier I (4) adopts SR445A high-speed preamplifier from SRS Company of the United States, the bandwidth is not less than 350MHz, and the input noise is not more than 2.8nV/Hz.

Photon counter Ⅰ (5) adopts SR400 photon counter from SRS Company in the United States, the counting rate can reach 200MHz, the counting channel is equipped with a gate generator, and the time setting range is 5ns～1s. In one scan, SR400 can be programmed to achieve a cycle of 1 to 2000 counting cycles, and the built-in RS-232 interface and GPIB interface are convenient for controlling the device and retrieving data.

The role of the monochromator (6) is to disperse the light beam into monochromatic light for spectral analysis. The selected monochromator has a spectral range of 0.4 μm to 0.8 μm, a spectral resolution of 2nm±1, a wavelength position repeatability of ±1nm, and an NA value of is 0.4.

The photodetector II (7) adopts the R2949 photomultiplier tube of Hamamatsu Company in Japan, cooperates with the electric refrigerator C9144, the dark count rate is less than 15photons/s, the side window opening is 6mm×6mm, and the front end is equipped with a visual function _ηλ filter The chip can remove the spectrum other than 0.4μm ~ 0.8μm.

The preamplifier II (8) adopts SR445A high-speed preamplifier from SRS Company of the United States, the bandwidth is not less than 350MHz, and the input noise is not more than 2.8nV/Hz.

Photon counter II (9) adopts SR400 photon counter from SRS Company of the United States, the counting rate can reach 200MHz, the counting channel is equipped with a gate generator, and the time setting range is 5ns～1s. In one scan, SR400 can be programmed to achieve a cycle of 1 to 2000 counting cycles, and the built-in RS-232 interface and GPIB interface are convenient for controlling the device and retrieving data.

The data processor (10) processes the two-way output data, that is, calculates the illuminance according to the ultra-weak starlight illuminance mathematical model:

Among them, E—illuminance, unit lx;

A—absolute spectral efficiency value of monochromatic light (wavelength 507nm) under scotopic conditions, lm;

h—Planck's constant, J/s;

c—the speed of light in vacuum, m/s;

M—the total amount of photon counts counted by the photon counter I (5);

S—the entrance pupil area of the optical lens, m ² , refers to the area of the aperture of the diaphragm, specifically S=(ΠD ² )/4;

η _λ - the visual function of monochromatic light with wavelength λ;

λ—wavelength of incident light, m, its value range is 0.4μm～0.8μm, so λ ₁ =0.4μm, λ _n =0.8μm;

k _λ —the proportion coefficient of the number of photons with a wavelength of λ in the total photon count, specifically the number of photons with a wavelength of λ counted by the photon counter II (9) and the number of photons with a wavelength of λ counted by the photon counter I (5) The ratio of the total number of photon counts.

The measuring method using this device specifically comprises the following steps:

Step 1. The incident light beam passes through the optical lens (1) to collect luminous flux, and the incident light beam is divided into two paths through the beam splitter (2).

Step 2: The incident light beam converges on the photosensitive surface of the photodetector I (3) for photoelectric conversion, and the incident light beam enters the monochromator (6) for dispersion and light splitting to obtain monochromatic light with a wavelength of λ.

Step 3: The photodetector Ⅰ (3) amplifies the output electrical signal through the preamplifier Ⅰ (4) to increase the amplitude of the signal; The number of photons is counted to obtain the total number of photon counts.

Step 4: The monochromatic light after dispersion and splitting converges on the photosensitive surface of the photodetector II (7) for photoelectric conversion, converting the optical signal into an electrical signal; the photodetector II (7) passes the output electrical signal through the front Put the amplifier II (8) to amplify the amplitude of the signal; then pass the photon counter II (9) to count the photons with high precision to obtain the number of photons with a wavelength of λ, which is compared with the total number of photons counted in step 4 , to obtain the proportion of photons of different wavelengths in the total photon count, and measure the light energy spectral distribution in the light beam to be measured, so as to improve the measurement accuracy of illuminance.

Step 5. Adjust the monochromator (6) to obtain monochromatic light with different wavelengths, and repeat steps 3 and 4.

Step 6: The measured values of photon counter I (5) and photon counter II (9) are transmitted to the data processor (10) as input data, and the illuminance is obtained by using the mathematical model of ultra-weak starlight illuminance.

In summary, the present invention provides a device and method for measuring ultra-weak starlight illuminance. The device uses two measurement channels to count and measure the number of photons, obtain the total amount of photon counts and obtain the photon number of monochromatic light at the same time. Obtain the proportion of photons of different wavelengths in the total photon count, and count accurately at the same time, without repeated measurement, and measure the light energy spectral distribution in the light beam at the same time, which can improve the accuracy of illuminance measurement and can achieve 10 ^-13 lx ultra-weak starlight illuminance Measurement.

Although the present invention has been described in detail in conjunction with preferred embodiments, those skilled in the art should understand that various modifications are allowed without departing from the spirit and essence of the present invention, and they all fall into the present invention. within the scope of protection of the claims.

Claims (8)

1. An ultra-weak starlight illuminance measuring device, characterized in that it comprises an optical lens (1), a beam splitter (2), a measurement channel I, a measurement channel II and a data processor (10); The optical lens (1) is connected to the beam splitter (2), and the measurement channel I and the measurement channel II are respectively connected between the beam splitter (2) and the data processor (10); The measurement channel I includes a photodetector I (3), a preamplifier I (4) and a photon counter I (5); The photodetector I (3) is connected with the beam splitter (2), followed by the preamplifier I (4) and the photon counter I (5), and the photon counter I (5) and the data processor (10 ) are connected; The measurement channel II includes a monochromator (6), a photodetector II (7), a preamplifier II (8), and a photon counter II (9); The monochromator (6) is connected to the beam splitter (2), and the monochromator (6) is sequentially connected to the photodetector II (7), the preamplifier II (8) and the photon counter II (9), and the photon The counter II (9) is connected with the data processor (10). 2. a kind of ultra-weak starlight illuminance measuring device according to claim 1, is characterized in that, described optical lens (1) comprises an aperture, and the aperture of aperture is the circle through hole of diameter D, and this aperture The diameter D of the light-through hole is the effective diameter of the optical lens (1). 3. A kind of ultra-weak starlight illuminance measuring device according to claim 2, characterized in that, the effective aperture D of the optical lens (1) is smaller than the exit pupil size D' of the starlight simulator, and the field angle 2β is larger than the incident light beam The divergence angle 2α. 4. A kind of ultra-weak starlight illuminance measuring device according to any one of claims 1-3, characterized in that, the optical aperture of the beam splitter (2) is 20mm × 20mm × 20mm, coated with a semi-reflective and semi-permeable film 0.4μm-0.8μm optical anti-reflection film is coated on the light incident and exit surfaces, and the transmittance of a single surface is not less than 98%. 5. A kind of ultra-weak starlight illuminance measuring device and method according to any one of claim 4, characterized in that, the monochromator (6) has a spectral range of 0.4 μm to 0.8 μm, a spectral resolution of 2 nm ± 1, and a wavelength The position repeatability is ±1nm, and the NA value is 0.4. 6. A method for measuring ultra-weak starlight illumination using the measuring device described in claim 1-5, characterized in that, comprising the following steps: Step 1. The incident light beam passes through the optical lens (1) to collect the luminous flux, and the incident light beam is divided into two paths through the beam splitter (2); Step 2. The incident light beam converges on the photosensitive surface of the photodetector I (3) for photoelectric conversion and outputs an electrical signal; the other path enters the monochromator (6) for dispersion and light splitting to obtain a monochromatic light beam with a wavelength of λ. Light; Step 3: The photodetector Ⅰ (3) amplifies the output electrical signal through the preamplifier Ⅰ (4); then the photon counter Ⅰ (5) counts the photons with high precision, counting the number of photons of the incident light, Get the total number of photon counts; Step 4: The monochromatic light after dispersion and splitting converges on the photosensitive surface of the photodetector II (7) for photoelectric conversion, converting the optical signal into an electrical signal; the photodetector II (7) passes the output electrical signal through the front Place the amplifier II (8) to amplify; then count the photons through the photon counter II (9) to obtain the number of photons with a wavelength of λ, and measure the light energy spectral distribution in the beam to be measured; Step 5, adjusting the monochromator (6), then monochromatic light of different wavelengths can be obtained, repeating steps 3 and 4; Step 6: The measured values of photon counter I (5) and photon counter II (9) are transmitted to the data processor (10) as input data, and the illuminance is obtained by using the mathematical model of ultra-weak starlight illuminance. 7. The ultra-weak starlight illuminance measurement method according to claim 6, characterized in that, the ultra-weak starlight illuminance mathematical model is: $\mathrm{<span\; class="notranslate">\; E.</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; A</span>}\mathrm{<span\; class="notranslate">\; h</span>}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; S</span>}}{<span\; class="notranslate">\; \&Integral;</span>}_{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}^{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}}{\mathrm{<span\; class="notranslate">\; \&eta;</span>}}_{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; \&lambda;</span>}$ Among them, E—illuminance; A—absolute spectral efficiency value of monochromatic light (wavelength 507nm) under scotopic conditions; h—Planck's constant; c—the speed of light in vacuum; M—the total amount of photon counts counted by the photon counter I (5); S—the area of the entrance pupil of the optical lens, which refers to the area of the aperture of the diaphragm, specifically S=(ΠD ² )/4; η _λ - the visual function of monochromatic light with wavelength λ; λ—wavelength of incident light; k _λ —the proportion coefficient of the number of photons with a wavelength of λ in the total photon count. 8. the ultra-weak starlight illuminance measurement method according to claim 7, is characterized in that, described k _λ is the number of photons of λ and the number of photons counted by photon counter I (5) for the wavelength obtained by photon counter II (9) The resulting ratio of the total number of photon counts.