RU2640751C2 - Device for recording sample emission in middle range of infrared spectrum - Google Patents

Abstract

FIELD: measuring equipment.SUBSTANCE: device for recording the sample emission in the middle range of the infrared spectrum comprises an external radiation source, a condenser system, the first flat mirror, a spherical mirror. An IR-array with the possibility of longitudinal and transverse displacement relative to the rays emanating from the second flat mirror is used as the recording system. The array is placed behind the focal plane of these rays. The distance from the focal plane to the receiving system is such that the diameter of the IR-emission beam coincides or is close to the size of the entrance window of the recording array.EFFECT: increased information content of the registered emission spectra and simplified device.5 dwg

Description

The proposed device relates to the field of physics - nonlinear optics, namely to spectral measuring technique, and can be used to study the structure of substances in liquid and solid states from infrared (IR) emission spectra in the middle wavelength range.

The registration of IR emission spectra from test samples began relatively recently, in the middle of the last century, when a highly sensitive IR Fourier technique appeared. In order to obtain IR emission from the samples, it was necessary to heat metal surfaces to temperatures of 100 ° C and higher. In this case, the recorded spectra were the total emission spectra of the metal substrate and the IR emission spectra of the sample. Non-heat-resistant and biological samples due to their destruction at high temperature were not used.

A useful model is known for recording the infrared emission spectrum of a sample [1], which contains an external source of monochromatic radiation, an object plane, a toroidal mirror optically coupled to an object plane and a plane mirror, which is located on the same axis as the receiving optical system of the IR-Fourier recording spectrometer.

The disadvantages of this device are the complexity of the optical and recording circuits, as well as technical procedures for servicing optics and sample preparation.

The closest solution to the technical nature and the achieved effect, selected as a prototype, is a useful model for recording the infrared spectrum of the emission of a sample [2], containing a condenser system located on the same optical axis as a radiation source and a plane mirror optically connected to the sample plane, which coupled to a spherical mirror optically coupled to a second plane mirror, from which the rays travel through a series of auxiliary optical elements to a compact recording system, including iris and sensitive IR receiver.

The disadvantage of the prototype is the slow speed of recording spectra due to the inertia of the stepper motor used for the mechanical opening of the iris diaphragm. The technical task of the solution is to simplify the scheme of the utility model, reduce its size and increase the speed of work.

The problem is achieved in that for recording the IR spectrum of the emission of the sample, a simpler optical scheme and a fundamentally different registration system is used, which is an application of a sensitive infrared matrix with 32 × pixels that fixes the angular spectral distribution of infrared radiation 31 with the possibility of longitudinal and transverse movement relative to the projection plane of the measured IR emission signal.

The invention is illustrated by the following figures:

in FIG. 1 shows a schematic optical diagram of a device;

in FIG. 2 shows a general view of an IR emission spectrometer;

in FIG. 3 shows the spectrum of polystyrene recorded in the range (600-1600 cm ^-1 ) recorded on the model of the proposed device (upper curve) and on a traditional IR-Fourier spectrometer (lower curve);

in FIG. 4 shows the spectrum of polystyrene recorded in the spectral range (1500-2800 cm ^-1 ) recorded on the model of the proposed (upper curve) and on a traditional IR-Fourier spectrometer (lower curve);

in FIG. 5 shows a block diagram of a matrix scan of an infrared emission signal:

IR lens - 9, a matrix of IR receivers - 10; matrix thermal stabilization unit - 11;

electronic control circuits - 12, 13.

The proposed model (Fig. 1) contains: a radiation source 1 (a source of coherent or incoherent light, any discharge lamp - mercury, xenon); condenser system 2; interchangeable filter - 3; the first flat mirror 4, located at an angle of 45 ° to the subject plane; 5 - a subject plane with a substrate with a test sample applied to it of any thickness, transparency, liquid or solid; a spherical mirror 6 and a second flat mirror 7; the perceiving system - matrix 8 (number of pixels 32 × 31), the computer processing the IR signal.

The proposed new solution allowed to increase the performance of the device by 100 times. This greatly expands the capabilities of this class of devices. The reduction in comparison with the number of optical-mechanical elements declared in RF patent No. 2345332 additionally increases the aperture ratio of the optical scheme of the utility model and provides an unsurpassed signal-to-noise ratio during such studies. The prototype of the IR-emission utility model is running developed software with a developed administration and security system for electronic data. The package provides data collection, their processing, including quantitative analysis and spectral search. A general view of the model of an IR emission spectrometer is shown in FIG. 2.

An important parameter of any spectral instrument is its resolution. To change the resolution and determine the exact numerical values of the spectral resolution of the utility model, mobile optical-mechanical structures were used. Changing the relative position of the IR matrix with respect to the sample along the IR beam made it possible to start the IR beam on the IR matrix or direct only a part of the radiation emanating from the sample. This makes it possible to vary the spectral resolution.

For example, if a large spectral interval falls on the IR matrix, then for a given (1064) number of pixels on the matrix, this leads to a resolution of 40 cm ⁻¹ . If you move the matrix (move further away from the intermediate focus) so that the spectral gap on the matrix decreases, then the resolution increases to 4 cm ^-1 . The shift of the IR matrix perpendicular to the direction of signal emission allows us to consider other parts of the spectrum with the same spectral resolution (4 cm ^-1 ). In FIG. Figures 3 and 4 in the upper part show examples of spectra of the same sample (polystyrene film) in different spectral ranges and with different spectral resolutions. In the spectra recorded on the proposed device (Figs. 3 and 4), the abscissa axis represents the angular size in pixels, and the ordinate axis represents the intensity of the infrared signal in arbitrary units. For comparison, below in FIG. Figures 3 and 4 show the polystyrene spectra obtained on a traditional IR Fourier spectrometer in the range 1600-600 cm ^-1 (Fig. 3) and 2800-1500 cm ^-1 (Fig. 4).

To change the spectral range, the introduction of mobile optical-mechanical elements was required. Thus, it was experimentally shown that by varying the layout of the elements of the useful layout, with the same limited set of matrix pixels, different spectral resolution can be obtained.

It can be seen that between the spectral characteristics obtained on a traditional IR Fourier spectrometer and the developed useful model, there is a certain similarity in the number and position of the peaks, as well as the intensity distribution between the peaks, which suggests that the developed model of the IR emission spectrometer is suitable for the study of samples in the infrared region.

Test measurements using the utility model were also performed on liquid samples of benzene C ₆ H ₆ and carbon tetrachloride CCL ₄ and their spectral characteristics were investigated. Both substances - benzene C ₆ H ₆ and carbon tetrachloride CCL ₄ are widely known spectroscopic objects and were used by us as standards. The comparative assignment of the bands showed a good match.

The above images in FIG. 3 and 4 show the quality of the obtained spectra and the capabilities of the utility model depending on the tasks.

The device operates as follows: spectrally broadband optical radiation from source 1 is focused by a system of condensers 2 through replaceable filters 3 onto a flat mirror 4, which reflects focused radiation onto the object plane with sample 5. Under the influence of radiation of the optical range in the sample, excitation and emission of IR quanta . IR emission is collected by a spherical mirror 6, formed into a slightly divergent beam and sent to a flat mirror 7, which then falls on the IR matrix 8, which registers the angular distribution of the spectral composition of IR radiation and visualizes the signal, which is further processed by a computer using software , which controls the matrix and records the spectra of the sample in the desired format.

The essence of the technical solution is as follows. Partially coherent low-intensity radiation from a visible light source is focused in the plane of the sample and excites molecular vibrations that induce IR emission, which, as the exciting radiation, has conical symmetry. The IR matrix is located orthogonal to the direction of the emission of infrared radiation, having the form of concentric rings of different diameters. The rings of small diameter correspond to low-frequency vibrations, and the rings of larger diameter correspond to high-frequency vibrations.

Since when using a gas discharge lamp with a polychromatic spectrum as a source of exciting radiation, all modes in the sample are excited, it is possible to detect not only IR-emission active vibrations, but also vibrations active in Raman scattering. Matrix (8) has the ability to move along the axis of the IR emission beam, and the resolution of the recorded spectra changes, as well as across the beam, and then the necessary part of the spectrum is recorded. This makes it possible, depending on the tasks, to additionally quickly take the spectrum in parts, but with an increased resolution or the entire spectrum with a lower spectral resolution.

The quality of the IR emission spectrometer depends on several factors, and one of the most important is the combination of the optical components with the matrix. They determine the image quality of the radiation source and determine the spectral resolution of the IR - emission spectrometer. A model was created and tested to record emission spectra. The visible light source is a 100 W xenon lamp, the rays from which were focused by a system of short-focus lenses with a diameter of 20 mm. A 32 × 31 pixel matrix was installed in the path of converging beams from the second plane mirror at a distance at which the size of the infrared emission beam coincided in size with the input window of the matrix 9 (Fig. 5), thereby completely using all the radiation coming from the matrix sample. In FIG. 5 shows a block diagram of an IR matrix, which contains: IR lens - 9; matrix of IR receivers - 10; matrix thermal stabilization unit - 11; electronic control circuits - 12, 13.

To increase the spectral resolution it is possible to use a matrix with a large number of pixels, but this will result in a significant increase in the cost of the utility model.

The proposed utility model, in comparison with the prototype, has the following advantages:

- it is more compact compared to the prototype, because it contains a smaller number of optical and electronic elements. In particular, the iris, stepper motor and pyroelectric receiver are not used. The pyroelectric receiver used in the registration system of the prototype does not function continuously, but only in pulsed mode so that its signal does not go beyond the dynamic range. To do this, a modulator was used - a signal chopper rotating at a frequency of 100 Hz, which complicated the model, slowed down the processing time of the useful signal by the computer, and also increased its dimensions. The dimensions of the proposed model are 300 × 200 × 100 cm;

- the model has a simpler optical design, cheaper to manufacture, more portable, the above dimensions make it convenient and portable;

- thanks to the use of the matrix, it became possible to quickly and automatically obtain survey spectra in the region of 400-3000 cm ^-1 with a resolution of about 40 cm ^-1 or to record in detail any part of the spectrum, but with a better resolution of about 4 cm ^-1 . This makes the registration of spectra faster, which simplifies and facilitates the operation of the model and creates ease of use and with fewer measurement errors.

Thus, the task has been successfully achieved.

Information sources

1. “Preliminary Studies of Laser-Induced Thermal Emission Spectroscopy of Condensed Phases”, L.T. Lin, D.D. Archibald and D.E. Honigs, Applied Spectroscopy, Volume 42, No. 3, 1988.

2. The prototype. RF patent No. 2345332 dated January 27, 2009. A device for recording the infrared spectrum of the emission of a sample. Authors Terpugov E.L., Degtyareva O.V., Khorokhorin A.I., Savransky V.V., Mitrokhin I.A., Akhmetov V.A. Application No. 2007112801.

Claims (1)

A device for recording emission of a sample in the mid-range of the infrared spectrum, containing an external radiation source and followed by a condenser system and a first plane mirror optically coupled to this system and the plane of the sample, a spherical mirror that is associated with the plane of the sample and the second plane mirror, characterized in that an IR matrix is used as a recording system with the possibility of longitudinal and transverse movement relative to the rays emanating from the second plane mirror, and It is located behind the focal plane of these rays, and the distance from the focal plane to the receiving system is such that the diameter of the infrared emission beam is the same or close to the size of the input window of the recording matrix.

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