CN106404695B - Spectrophotometer - Google Patents

Abstract

The spectrophotometer provided by the invention has the advantages of large dynamic measurement range, high measurement precision and high repeatability precision, so that the spectrophotometer has a wider application prospect.

Description

Spectrophotometer

technical field

The present invention relates to a photometer, in particular to a spectrophotometer, which has an ultra-large dynamic measurement range and ultra-high measurement accuracy.

Background technique

则待测样品的透射率T可按照公式 (1.1)计算：The core technology of spectrophotometer is to measure the transmittance and reflectance of light at a specific wavelength or within a certain wavelength range, which is widely used in physics, chemistry, biology, medicine, materials science, environmental science, as well as in chemical industry, medicine, environment Detection, metallurgy and other modern industrial production and management departments have obtained a wide range of important applications. At present, the spectrophotometer generally adopts the measurement framework of the double optical path photometry, as shown in Figure 1, which mainly includes a polychromatic light source 1, a monochromator 2, a diaphragm 3, a polarizer 4, a beam splitter 5, an attenuation plate 6, a focusing Lens 7, reference light detector 8, sample holder 9, sample 10, focusing lens 11, test light detector 12. The polychromatic light emitted by the polychromatic light source 1 passes through the monochromator 2 to form the monochromatic light required for the measurement. The monochromatic light passes through the diaphragm 3 and the polarizer 4 to form the linearly polarized light required for the measurement, and the linearly polarized light passes through the beam splitting. After the detector 5, a beam of measurement light and a beam of reference light are formed. The reference light is collected by the reference photodetector 8 after passing through the attenuation plate 6 and the focusing lens 7, and the test light is received by the test photodetector after passing through the sample 10 and the focusing lens 11. . In the existing spectrophotometer, the measurement method and measurement principle of the sample transmittance are as follows: first, when the sample is not placed in the measurement beam and the reference beam, the reference beam and the test beam are used to simultaneously collect the light of the reference beam and the test beam. Intensity, denoted as I ₁ and I ₂ respectively, then place the sample to be tested in the test optical path, and use the reference photodetector and the test photodetector to simultaneously collect the light intensities of the reference beam and the test beam, respectively denoted as and

Then the transmittance T of the sample to be tested can be calculated according to formula (1.1):

Use a monochromator to gradually change the wavelength λ of the incident light, and measure the transmittance of the sample at different wavelengths in turn to obtain the transmission spectrum T(λ) of the sample to be measured.

However, the existing commonly used spectrophotometers mainly have the following shortcomings:

(1) High transmittance and high reflectivity cannot be measured accurately. Due to the limitations of the existing spectrophotometer measurement principle and measurement accuracy, the highest transmittance and highest reflectivity can be measured in general at 99.8%, but for samples with higher transmittance and reflectivity, such as reflectivity higher than 99.9% The high-reflection film and the anti-reflection film with a transmittance higher than 99.9% cannot be accurately measured by the current spectrophotometer.

(2) Ultra-low transmittance and ultra-low reflectivity cannot be accurately measured. When measuring low transmittance and low reflectivity (such as optical components with R < 4%), the existing spectrophotometer generally selects fused silica glass with known theoretical reflectivity as the reference sample, so that the low transmittance can be measured. The relative measurement accuracy of optical elements with low reflectivity and low reflectivity is improved to 1%, but the lowest transmittance and reflectivity that can be measured by this method is about 0.5%, for optical elements with lower transmittance and reflectivity, such as residual reflectivity The anti-reflection coating below 0.1% and the high-reflection coating with residual transmittance below 0.1% cannot be accurately measured by the current spectrophotometer.

(3) The measurement accuracy of transmittance and reflectivity is not high. For the transmittance and reflectivity of common optical components, the measurement accuracy of existing spectrophotometers is about 0.2% to 0.5%, while in many applications, the measurement accuracy of transmittance and reflectivity is required to be better than 0.1%, which makes Current spectrophotometers cannot meet these testing needs.

SUMMARY OF THE INVENTION

In order to solve the problems existing in the existing spectrophotometer, the present invention provides a spectrophotometer, which has the characteristics of a large dynamic measurement range and high measurement accuracy and repeatability.

The technical solution of the present invention is as follows:

A spectrophotometer is characterized by comprising a light source module, a reference light module, a photoelectric detection module, a resonant cavity module and a sample module:

The light source module includes a tunable laser and a pulsed laser. The laser output direction of the tunable laser is followed by a laser power adjustment device, a monochromator, a first beam splitter, a diaphragm, a polarizer and a chopper. The laser output direction of the pulsed laser is the first beam splitter, diaphragm, polarizer and chopper;

The reference light module includes a second beam splitter, and the second beam splitter is arranged on the output optical path of the light source module. The second beam splitter divides the incident beam into a reflected beam and a transmitted beam, and the second beam splitter divides the incident beam into a reflected beam and a transmitted beam. The reflected beam of the beamer, that is, the propagation direction of the reference laser beam is an attenuator, a first focusing lens and a reference light detector placed at the focus of the first focusing lens in sequence;

The resonant cavity module consists of a first convex lens, a small aperture diaphragm placed at the focal position of the first convex lens, a second convex lens with a focal point located at the small aperture diaphragm, cavity mirror M1 and cavity mirror M2 in order from the incident light to the outgoing light. , the first convex lens, the aperture diaphragm and the second convex lens form a mode matching unit, and the cavity mirror M1 and the cavity mirror M2 coated with the high reflection film form an optical resonant cavity;

The sample module is composed of a sample clamping and attitude adjustment device and a sample to be tested;

The photoelectric detection module includes a third beam splitter, the third beam splitter is arranged in the transmitted beam direction of the second beam splitter, and the third beam splitter divides the incident beam into a reflected beam and a transmitted beam. The beam, the reflected beam direction of the third beam splitter is a mirror, a second focusing lens, an integrating sphere, a photodetector and a lock-in amplifier in sequence, the integrating sphere is placed at the focus of the second focusing lens, and the The transmitted beam direction is the first convex lens of the resonant cavity module;

The laser output direction of the optical resonant cavity is followed by a third focusing lens, an ultrafast photodetector and an oscilloscope, and the ultrafast photodetector is located at the focus of the third focusing lens.

When using photometry to measure the transmittance, reflectivity, ultra-low transmittance and ultra-low reflectivity of ordinary optical components, tunable lasers and monochromators are mainly used to provide light sources for the measurement system. The pulsed laser provides a pulsed laser source for the measurement, while the tunable laser and the monochromator provide the indicator laser for the measurement, and the indicator laser is used for the adjustment and assembly of the resonator. The function of the laser power adjustment device is to adjust the power of the test laser correspondingly according to the specific measurement object, so that the light intensity collected by the test photodetector is in the optimal linear working range of the optical power meter. The polarizer provides the beam with the required polarization state for the measurement object, and the function of the chopper is to modulate the measurement laser into a laser beam with a certain natural frequency during ordinary photometric measurement.

The reference light module mainly includes an adjustable attenuator, a first focusing lens and a photodetector. The attenuator mainly adjusts the intensity of the reference beam according to the intensity of the test beam, so as to match the intensity of the test beam and the reference beam. , and they are all in the best linear working area of the detector. The purpose of the first focusing lens is to focus the reference beam into a smaller spot and improve the measurement accuracy of the detector. The reference optical module is mainly used in the double-path photometric measurement. , real-time monitoring of laser power, which can eliminate the measurement error caused by laser power drift to photometry.

The resonant cavity module is mainly composed of a first convex lens, a pinhole aperture, a second convex lens, a cavity mirror M1 and a cavity mirror M2. The first convex lens, the pinhole aperture and the second convex lens form a mode matching unit, which is mainly used for pulsed laser light. The mode matching of the cavity mirror M1 and the cavity mirror M2 coated with the high reflection film constitute an optical resonant cavity.

The sample module is mainly composed of a sample fixing device and a sample to be tested. The sample adjustment mechanism (including linear motion and pitch and yaw adjustment functions) ensures that the system can accurately position and adjust the attitude of the components.

The photoelectric detection module is mainly composed of the second focusing lens, integrating sphere, test photodetector, lock-in amplifier, third focusing lens, ultrafast photodetector and oscilloscope. In ordinary photometric measurement technology, the test light is reflected or transmitted by the sample and then focused by the focusing lens, irradiated on the integrating sphere, and finally collected by the test photodetector. In the resonant cavity measurement technology, the test light passes through the focusing lens. After focusing, it is irradiated on the ultrafast photodetector, and the final signal is received by the oscilloscope.

The working principle of the present invention is as follows:

1. Measurement method of ordinary transmittance and ordinary reflectivity (0.5%-99.8%)

和

则光学元件的透射率T可按照公式 (1.1)计算得到。The measurement principle and measurement method of ordinary transmittance and ordinary reflectivity are as follows: first turn on the tunable laser, grating monochromator, chopper and reference photodetector, test photodetector and lock-in amplifier, turn off the pulsed laser, and then measure In the process, the test beam is directly collected by the test photodetector, and then the light intensity signal values of the reference light and the test light are simultaneously collected by the data collector, denoted as I ₁ and I ₂ respectively, and then the optical glass to be tested is placed in the In the test optical path, the transmitted beam is irradiated on the test photodetector, and the light intensity signal values of the reference light and the test light are simultaneously collected by the data collector, which are recorded as

and

Then the transmittance T of the optical element can be calculated according to formula (1.1).

2. Measurement method of high transmittance and high reflectivity (99.8%-99.999%)

The measurement principle and measurement method of high transmittance and high reflectivity are as follows: firstly turn on the tunable laser, grating monochromator, ultrafast detector and oscilloscope, pulse laser, when there is no sample in the cavity, after the pulse laser enters the resonator, The output signal of the optical cavity can be expressed as:

Among them, I(t) is the measured light intensity signal changing with time t, I ₀ is the initial value of light intensity, t

is the time variable, and τ is the ring-down factor of the resonator, which can be expressed as:

where n is the refractive index of the medium in the cavity, L is the cavity length, c is the speed of light, α is the absorption coefficient in the cavity, and R is the overall reflectivity of the cavity. When the medium in the cavity is air, the refractive index n is approximately 1. According to the ring-down time calculated by the ultrafast photodetector and the oscilloscope, the average reflectivity of the cavity mirror is calculated as follows:

In the formula, R ₁ is the reflectivity of the cavity mirror M1, and R ₂ is the reflectivity of the cavity mirror M2.

When the incident laser and the resonator mode are matched, and the incident laser pulse is short, the decay signal decays mono-exponentially. In order to measure the high reflectivity of the sample, the sample to be tested is usually placed in the resonator to form a folded cavity, and two measurements are performed separately. In this case, the ring-down signal of the resonator is obtained, and then the curve measured in the two cases is fitted according to the single exponential decay function, that is, the corresponding ring-down factors τ ₁ and τ ₂ are obtained, and the The reflectivity is:

3. Measurement method of low transmittance and low reflectivity (0.001%-0.5%)

和测试光的光强信号值

则光学元件的透射率 T按照公式(1.6)计算：The measurement principle and measurement method of low transmittance and low reflectivity are as follows: first turn on the tunable laser, grating monochromator, chopper and reference photodetector, test photodetector and lock-in amplifier, turn off the pulsed laser, A reference sample (with a reflectivity of R ₀ ) is placed in the beam, and an attenuator is placed in the reference optical path. During the measurement process, the test beam is directly collected by the test photodetector, and then the reference beam is simultaneously collected by the data collector. The strong signal value I ₁ and the light intensity signal value I ₂ of the test light are then removed, the reference sample is removed, the optical glass to be tested is placed in the test optical path, the transmitted beam is irradiated on the test photodetector, and the data collector is used to simultaneously collect Light intensity signal value of reference light

and the light intensity signal value of the test light

Then the transmittance T of the optical element is calculated according to formula (1.6):

Compared with the existing spectrophotometer, the present invention has the following advantages:

(1) Large dynamic measurement range

The system of the invention adopts the scheme of combining the ordinary photometric method and the resonant cavity measurement method, and utilizes the optical component that dynamically adjusts the reflectivity of itself, so that the measurement system has a large dynamic measurement range (0.001%-99.999%), and the system can not only Accurate measurement of high transmittance (99.8%＜T＜99.999% and high reflectivity (99.8%＜R＜99.999%), also can be used for ordinary transmittance (0.5%＜T＜99.8%) and ordinary reflectance It can also measure ultra-low transmittance (0.001% < T < 0.5%) and ultra-low reflectance (0.001% < R < 0.5%), which is Significantly expand the application field and scope of the instrument.

(2) Ultra-high measurement accuracy and repeatability

The invention adopts dual optical path autocorrelation technology, which not only successfully eliminates the influence of light source power fluctuations on the measurement results, but also significantly improves the noise and anti-interference ability of the system, and can significantly eliminate ambient stray light, dark current and preamplifier drift. The influence of reflectivity measurement results, the absolute measurement accuracy of ordinary transmittance and ordinary reflectivity reaches 0.1%, the relative measurement accuracy of ultra-low transmittance and ultra-low reflectivity is better than 1%, and the absolute measurement accuracy of high transmittance and high reflectivity Accuracy reaches 0.001%.

Description of drawings

FIG. 1 is a schematic diagram of the measurement optical path of a conventional spectrophotometer.

FIG. 2 is a schematic diagram of the optical path when the spectrophotometer of the present invention measures the transmission element.

FIG. 3 is a schematic diagram of the optical path when the spectrophotometer of the present invention measures the reflective element.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and embodiments, but the protection scope of the present invention should not be limited by this.

Example 1:

Fig. 2 is the optical path schematic diagram when the spectrophotometer of the present invention measures the transmission element, as can be seen from the figure, the spectrophotometer of the present invention comprises a light source module, a reference light module, a photoelectric detection module, a resonant cavity module and a sample module:

The light source module includes a tunable laser 13 and a pulsed laser 16. The laser output direction of the tunable laser 13 is followed by a laser power adjustment device 14, a monochromator 15, a first beam splitter 17, a diaphragm 18, and a polarizer. 19 and the chopper 20, the laser output direction of the pulsed laser 16 is the first beam splitter 17, the diaphragm 18, the polarizer 19 and the chopper 20;

The reference light module includes a second beam splitter 21. The second beam splitter 21 is arranged on the output optical path of the light source module. The second beam splitter 21 divides the incident beam into a reflected beam and a transmitted beam. The reflected beam of the second beam splitter 21, that is, the reference laser beam propagation direction is the attenuation plate 22, the first focusing lens 23 and the reference light detector 24 placed at the focal point of the first focusing lens 23 in sequence;

The resonant cavity module is, from the incident light to the outgoing light, a first convex lens 27, a small aperture diaphragm 28 placed at the focal position of the first convex lens 27, a second convex lens 29 with a focal point at the small aperture diaphragm 28, and a cavity mirror. M1 30 and the cavity mirror M233, the first convex lens 27, the aperture stop 28 and the second convex lens 29 form a mode matching unit, and the cavity mirror M1 30 and the cavity mirror M2 33 coated with a high reflection film form an optical resonant cavity ;

The sample module is composed of a sample clamping and attitude adjusting device 31 and a sample to be tested 32;

The photoelectric detection module includes a third beam splitter 25, the third beam splitter 25 is arranged in the transmitted beam direction of the second beam splitter 21, and the third beam splitter 25 divides the incident beam into The reflected light beam and the transmitted light beam, in the direction of the reflected light beam of the third beam splitter 25 are the mirror 26, the second focusing lens 34, the integrating sphere 35, the photodetector 36 and the lock-in amplifier 37 in sequence, and the integrating sphere 35 is placed in the At the focal point of the second focusing lens 34, in the direction of the transmitted beam is the first convex lens 27 of the resonator module;

The laser output direction of the optical resonator is the third focusing lens 38, the ultrafast photodetector 39 and the oscilloscope 40 in sequence, and the ultrafast photodetector 39 is located at the focus of the third focusing lens 38.

Example 2:

FIG. 3 is a schematic diagram of the optical path when the spectrophotometer of the present invention measures the reflective element. As can be seen from the figure, the spectrophotometer of the present invention includes a light source module, a reference light module, a photoelectric detection module, a resonant cavity module and a sample module:

The light source module includes a tunable laser 13 and a pulsed laser 16. The laser output direction of the tunable laser 13 is followed by a laser power adjustment device 14, a monochromator 15, a first beam splitter 17, a diaphragm 18, and a polarizer. 19 and the chopper 20, the laser output direction of the pulsed laser 16 is the first beam splitter 17, the diaphragm 18, the polarizer 19 and the chopper 20;

The reference light module includes a second beam splitter 21. The second beam splitter 21 is arranged on the output optical path of the light source module. The second beam splitter 21 divides the incident beam into a reflected beam and a transmitted beam. The reflected beam of the second beam splitter 21, that is, the reference laser beam propagation direction is the attenuation plate 22, the first focusing lens 23 and the reference light detector 24 placed at the focal point of the first focusing lens 23 in sequence;

The resonant cavity module is, from the incident light to the outgoing light, a first convex lens 27, a small aperture diaphragm 28 placed at the focal position of the first convex lens 27, a second convex lens 29 with a focal point at the small aperture diaphragm 28, and a cavity mirror. M1 30 and the cavity mirror M233, the first convex lens 27, the aperture diaphragm 28 and the second convex lens 29 form a mode matching unit, and the cavity mirror M1 30 and the cavity mirror M2 33 coated with a high reflection film form an optical resonant cavity ;

The sample module is composed of a sample clamping and attitude adjusting device 31 and a sample to be tested 32, and the sample to be tested 32 is a reflective element;

The photoelectric detection module includes a third beam splitter 25, the third beam splitter 25 is arranged in the transmitted beam direction of the second beam splitter 21, and the third beam splitter 25 divides the incident beam into The reflected light beam and the transmitted light beam, in the direction of the reflected light beam of the third beam splitter 25 are the mirror 26, the second focusing lens 34, the integrating sphere 35, the photodetector 36 and the lock-in amplifier 37 in sequence, and the integrating sphere 35 is placed in the At the focal point of the second focusing lens 34, in the direction of the transmitted beam is the first convex lens 27 of the resonator module;

In the laser output direction of the optical resonator, that is, the direction of the reflected light through the sample to be tested 32 is the third focusing lens 38, the ultrafast photodetector 39 and the oscilloscope 40 in sequence, and the ultrafast photodetector 39 is located at The third focusing lens 38 focuses.

The specific embodiments described above further describe the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above-mentioned specific embodiments are only specific embodiments of the present invention, and are not intended to limit the present invention. Within the spirit and principle of the present invention, any modifications, equivalent replacements, improvements, etc. made should be included within the protection scope of the present invention.

Claims (1)

1. The utility model provides a spectrophotometer which characterized in that includes light source module, reference light module, photoelectric detection module, resonant cavity module and sample module:

the light source module comprises a tunable laser (13) and a pulse laser (16), wherein a laser power adjusting device (14), a monochromator (15), a first beam splitter (17), a diaphragm (18), a polaroid (19) and a chopper (20) are sequentially arranged in the laser output direction of the tunable laser (13), and the first beam splitter (17), the diaphragm (18), the polaroid (19) and the chopper (20) are arranged in the laser output direction of the pulse laser (16);

the reference light module comprises a second beam splitter (21), the second beam splitter (21) is arranged on an output light path of the light source module, the second beam splitter (21) divides an incident light beam into a reflected light beam and a transmitted light beam, and an attenuation sheet (22), a first focusing lens (23) and a reference light detector (24) placed at the focus of the first focusing lens (23) are sequentially arranged in the propagation direction of the reflected light beam, namely the reference laser beam, of the second beam splitter (21);

the resonant cavity module comprises a first convex lens (27), a small hole diaphragm (28) arranged at the focus position of the first convex lens (27), a second convex lens (29) with the focus positioned at the small hole diaphragm (28), a cavity mirror M1(30) and a cavity mirror M2(33) in sequence from incident light to emergent light, wherein the first convex lens (27), the small hole diaphragm (28) and the second convex lens (29) form a mode matching unit, and a cavity mirror M1(30) and a cavity mirror M2(33) which are plated with high-reflection films form an optical resonant cavity;

the sample module consists of a sample clamping and posture adjusting device (31) and a sample (32) to be detected;

the photoelectric detection module comprises a third beam splitter (25), the third beam splitter (25) is arranged in the direction of a transmitted beam of the second beam splitter (21), the third beam splitter (25) divides an incident beam into a reflected beam and a transmitted beam, a reflector (26), a second focusing lens (34), an integrating sphere (35), a light detector (36) and a lock-in amplifier (37) are sequentially arranged in the direction of the reflected beam of the third beam splitter (25), the integrating sphere (35) is arranged at the focus of the second focusing lens (34), and a first convex lens (27) of the resonant cavity module is arranged in the direction of the transmitted beam;

and a third focusing lens (38), an ultrafast photoelectric detector (39) and an oscilloscope (40) are sequentially arranged in the laser output direction of the optical resonant cavity, and the ultrafast photoelectric detector (39) is positioned at the focus of the third focusing lens (38).

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