Disclosure of Invention
The invention aims to solve the technical problems that an instrument is known to be capable of measuring the refractive index of one wavelength only, and if the refractive index of other wavelengths is required to be measured, a light source is required to be replaced, so that the instrument is very troublesome.
A first object of the present invention is how to achieve an improved speed of prism coupling measurement by making refractive index measurements using a broad spectrum light source and a prism coupling method.
The technical scheme adopted is as follows:
A method for measuring refractive index by coupling a wide spectrum prism includes such steps as using the wide spectrum light from wide spectrum light source to enter a semicircular prism, putting the sample to be measured on the plane of said semicircular prism, applying a certain pressure to compress, making the reflected light on the plane of said semicircular prism enter a spectrometer, collecting spectrum by said spectrometer, and calculating the spectral data by wide spectrum prism coupling algorithm to obtain the refractive index of the material to be measured.
Preferably, the spectrum shortest wavelength of the broad spectrum light source isThe longest wavelength is,Should be greater than 100nm. The broad spectrum light source has a wider emission spectrum.
For the preferred embodiments of the present invention, the spectrum emitted by the broad spectrum light source has polarized or unpolarized characteristics.
The second object of the present invention is to provide a wide spectrum prism coupling measurement device, in which a wide spectrum light source is coupled with a semicircular prism to perform refractive index measurement, and a complete measurement can be obtained without rotating an angle adjustment table, so as to improve the speed of prism coupling measurement.
The technical scheme adopted is as follows:
The utility model provides a wide spectrum prism coupling measuring device, includes semi-circular prism and the anchor clamps of fixed semi-circular prism, and semi-circular prism is including having the arc surface that receives the incident light perpendicularly and placing the plane of sample that awaits measuring, and anchor clamps have the recess that agrees with semi-circular prism mutually, and the anchor clamps top sets up incident window and exit window corresponding to the arc surface of semi-circular prism, and the plane of semi-circular prism is exposed to the anchor clamps bottom opening.
For the optimization of the technical scheme of the invention, the top surface of the semicircular prism is an arc surface, the bottom surface is a plane, and both side surfaces are semicircular.
The clamp is preferably formed by two vertical plates and a plurality of reinforcing ribs connected with the two vertical plates, and grooves are formed between the vertical plates and the reinforcing ribs in a surrounding mode, so that the mechanical strength of the clamp is improved.
According to the technical scheme, the positioning grooves for clamping the side surfaces of the semicircular prisms are formed in the inner side surfaces of the two vertical plates, so that the clamping efficiency of the semicircular prisms is improved.
According to the technical scheme, the semicircular prism and the groove are fixed by gluing, so that the clamping strength of the semicircular prism is improved, and slipping is prevented.
For the optimization of the technical scheme of the invention, two vertical plates of the clamp are provided with screw holes for connecting an external mechanism.
Compared with the prior art, the invention has the following beneficial effects:
1. The method adopts a wide spectrum light source, and can obtain one-time complete measurement without rotating an angle adjusting table.
2. The method adopts a wide spectrum light source with various wavelengths, and can obtain the refractive indexes of materials with various wavelengths.
3. The device adopts the semicircular prism, no matter what angle the sample to be measured is placed, the incident light is perpendicular to the arc surface of the semicircular prism, so that refraction does not occur, the light is always positioned at the center of the semicircle and a fixed point on the sample, the change of the measuring position is avoided, the reflected light is also perpendicular to the arc surface, different refraction light is not generated due to chromatic dispersion, and the collection of a wide spectrum is easier.
Detailed Description
The technical scheme of the present invention is described in detail below, but the scope of the present invention is not limited to the embodiments.
In order to make the contents of the present invention more comprehensible, the present invention is further described with reference to fig. 1 to 12 and the detailed description below.
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
As shown in FIG. 1, the method for measuring the refractive index by coupling the wide-spectrum prism in the embodiment comprises the steps that broadband spectrum light emitted by a wide-spectrum light source enters a semicircular prism at a certain angle, a sample to be measured is placed on the plane of the semicircular prism and is pressed by applying certain pressure, reflected light on the plane of the semicircular prism enters a spectrometer, the spectrometer collects spectrum, and spectral data is calculated through a wide-spectrum prism coupling algorithm to obtain the refractive index of a material to be measured.
In the method for measuring the refractive index by coupling the wide-spectrum prism, the angle of the semicircular prism can be adjusted by the angle adjusting table, but because the wide-spectrum light source is adopted, the wide-spectrum prism can obtain complete measurement once without rotating the angle adjusting table, the measurement time is limited by the acquisition speed of the spectrometer, if a linear array type high-speed spectrometer is adopted, the time can be shortened to be within one second, the measurement speed is greatly improved, if more precise measurement is required, or the refractive index of a material to be measured is greatly changed, the angle adjusting table can be rotated, so that the critical angle is in the spectrum, and because the wide-spectrum light source with multiple wavelengths is adopted, the refractive index of the material with multiple wavelengths can be obtained. The above-described advantages provide a great advantage over conventional methods.
In the method for measuring refractive index by coupling the broad spectrum prism of the embodiment, the broad spectrum light source has a wider emission spectrum, and the shortest spectrum wavelength isThe longest wavelength is,Should be greater than 100nm. Light sources having these characteristics are tungsten halogen lamps, xenon lamps, mercury lamps like arc lamps, or white LEDs, or supercontinuum laser sources, or mode-locked ultrashort pulse frequency comb sources.
The spectrum emitted by the broad spectrum light source has polarized or unpolarized characteristics. When the spectrum has polarization characteristics, the refractive index of the birefringent material can be measured, and when the spectrum has non-polarization characteristics, the orthogonal polarization can be selected by the broadband polarizer, and the refractive index of the birefringent material can be measured.
As shown in fig. 2, the wide-spectrum prism coupling measuring device includes a semicircular prism 1 and a jig 2 for fixing the semicircular prism. The semicircular prism 1 in the wide-spectrum prism coupling measuring device does not have straight edge characteristics such as a triangular prism, the semicircular prism 1 comprises an arc surface 11 which vertically receives incident light and a plane 12 for placing a sample to be measured, and specifically, the top surface of the semicircular prism 1 is an arc surface 11, the bottom surface of the semicircular prism is a plane 12, and two side surfaces 13 are semicircular.
As shown in fig. 3, since the light source of the present invention is a wide spectrum light source, if a straight edge prism is used, the incident light source will generate different refraction angles due to chromatic dispersion, so that there are many problems in measuring position, reflected light collection, etc. According to the semicircular prism 1, no matter what angle the sample to be measured is placed, the incident light is perpendicular to the arc surface, so that refraction does not occur, the light is always positioned at the center of a semicircle and a fixed point on the sample, and the change of the measuring position is avoided. Moreover, the reflected light is also perpendicular to the arc surface, so that different refraction light can not be generated due to dispersion, and the collection of a broad spectrum is easier. In addition, the semicircular prisms should be made of a material having a relatively large refractive index, such as rutile.
As shown in fig. 4, the semicircular prism 1 is clamped by a jig 2, and the jig 2 is made of a material which has a certain strength and is easy to process, such as metal, plastic, resin, etc.
The fixture 2 has a groove that fits with the semicircular prism 1 and has two windows for entrance and exit. The bottom of the fixture is provided with a window, the plane 12 of the semicircular prism 1 is exposed, and the fixture is attached to the sample 3 to be tested.
As shown in fig. 4 and 5, the jig 2 is composed of two upright plates 23 and a plurality of reinforcing ribs 24 connecting the two upright plates, and a groove is defined between the upright plates 23 and the reinforcing ribs 24. The semicircular prism 1 is clamped in the groove, the semicircular prism 1 can be fixed in the groove by mechanical clamping, gluing and other methods, and the groove is formed by surrounding the vertical plate 23 and the reinforcing ribs 24, so that the mechanical strength of the clamp is further improved.
As shown in fig. 5, the inner side surfaces of the two vertical plates 23 are provided with positioning grooves 231 for engaging with the side surfaces of the semicircular prism 1, thereby further improving the installation efficiency.
As shown in fig. 6 and 7, in this embodiment, the sample 3 to be measured is attached to the plane 12 of the semicircular prism 1, and a support is provided below the sample 3 to be measured, and a certain pressure is applied by air floatation, a spring, or the like to compress the sample 3 to be measured. The manner of fixing the sample 3 to be measured described here is known to the person skilled in the art.
As shown in fig. 8, in this embodiment, the fixture 2 may be placed upside down so that the sample 3 to be measured is located above the semicircular prism 1. Similarly, the fixture 2 can be placed at the side, so that light rays can be transmitted in the horizontal plane.
As shown in fig. 6, specifically, the clamp 2 is connected with the angle adjusting mechanism by a mechanical connection method, and the clamp 2 and the angle adjusting mechanism are fixed by screw holes formed on two vertical plates 23 on the clamp 2. The angle adjusting mechanism consists of a stepping motor, a servo motor and the like, and can read the current angle. The construction of the angle adjustment mechanism described herein, as well as the angular display and reading, are known to those skilled in the art.
In the method for measuring refractive index by coupling the broad spectrum prism of the embodiment, the spectrometer is realized by adopting a scanning spectrometer, a linear array fixed spectrometer, a Fourier transform spectrometer and the like. The linear array fixed type spectrometer with higher scanning speed is preferable. The spectrometer collects the light emitted by a wide-spectrum light source and reflected by a prism planeTo the point ofIs provided).
Further, in the method for measuring refractive index by coupling the broad spectrum prism in this embodiment, since the spectrum emitted by the broad spectrum light source is not flat, the value of the reflectivity cannot be directly obtained, and the spectrum needs to be calibrated and normalized. The calibration and normalization is achieved by (1) collecting the original spectrum of the broad spectrum light source, (2) dividing the measured spectrum by the original spectrum in terms of wavelength.
The method for collecting original spectrum of wide spectrum light source can be one of ① splitting wide spectrum light source by optical fiber beam splitter in advance, wherein one beam enters into spectrometer for spectrum collection, ② collecting spectrum with partial intensity by space turning by beam splitting lens and reflecting partial intensity into spectrometer, ③ rotating prism to angle with larger incidence angle without placing sample, and collecting spectrum with wide spectrum light sourceTo the point ofIs totally reflected, and the original spectrum of the reflection is collected.
The preferred method ① of the present invention. As shown in fig. 10, the Original spectrum Original is obtained by method ①, and then Normalized by dividing the measured spectrum by the Original spectrum.
Specific examples:
the process of the invention will be further described with BK7 glass as an example.
The wide spectrum light source of this example adoptsTo the point ofThe super-continuum spectrum laser light source of the system is characterized in that the wide-spectrum light source is split by an optical fiber, one beam of the light source enters a semicircular prism 1 after being collimated to collect measurement spectrum, and the other beam of the light source enters an optical fiber spectrometer to collect original spectrum.
The semicircular prism 1 is made of rutile material, the refractive index of the rutile is known, the data of the semicircular prism 1 can be fitted according to formulas (1) - (4), and parameters related to prism coupling can be given by a Fresnel formula:
for critical angles, there are
(1)
Wherein,As the critical angle is set to be the critical angle,、The refractive index of the medium in which the incident light and the outgoing light are located, respectively.
Reflectivity for P-polarization and S-polarizationAndRespectively have
(2)
(3)
Wherein,For the complex amplitude of the reflectivity of the P-polarization,For the complex amplitude of reflectivity of the S-polarization,For the electric field strength of the P-polarized reflected light,For the electric field strength of the P-polarized incident light,For the electric field strength of the S polarized reflected light,For the electric field strength of S-polarized incident light,For the refractive index of the incident medium,In order to refract the medium in refractive index,For the measured angle of incidence,Is the measured refractive angle.
And the angles of incidence and refraction follow snell's law:
(4)
The prism coupling process can be calculated according to the above formulas (1) - (4), and the refractive index and other parameters can be back-deduced.
BK7 glass was placed on the plane of the semicircular prism and abutted. Calculate and select the appropriate measured angle of incidence and rotate into place according to equation (1), in this embodimentSelect at critical angleThe vicinity includes a critical angle.
And turning on a broad spectrum light source and a spectrometer for measurement. As shown in fig. 11, an Original spectrum BK7 Original is obtained, and then a Normalized spectrum BK7 Normalized is obtained by dividing the measured spectrum by the Original spectrum.
The raw spectral data collected by the spectrometer is shown as BK7 Original in FIG. 11. As shown in FIG. 11, the original spectrum at less than about 0.6 μm, the refractive index of rutile is much greater than BK7 due to dispersion, and the semicircular prism planes produce total reflection, with a reflectivity of 1.0. In contrast, when the spectrum is greater than about 0.6 μm, the semicircular prism planes are not in the total reflection range and the reflectivity varies with wavelength.
Specifically, during measurement, the angle between the semicircular prism 1 and the incident light of the light source is adjusted, namelyIn an embodiment of the present invention,Is obtained by the formula (1) according to the above measured angle, and in general, the measured angle of incidence is selectedAt critical angleNearby. First selecting a wavelengthAt the position ofTo the point ofBetween, andIs relatively close to. Calculating wavelengthCritical angle of (2). Rotating the semicircular prism to make the incident angle be critical angleThen, measurement is performed.
The sample material to be tested is replaced by Schott glass. The above measurement steps are repeated and normalized data is obtained as shown in fig. 12. It can be seen that critical angles of Schott glass and BK7 glassWith differences. The difference represents the refractive index difference of the materials. After normalized data is obtained, curve fitting is performed by formulas (1) - (4), fitting materials atTo the point ofIs a refractive index of (c).
The above embodiments are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereto, and any modification made on the basis of the technical scheme according to the technical idea of the present invention falls within the protection scope of the present invention.