RU25598U1 - INSTALLATION FOR DETERMINING THE ELECTROMAGNETIC RADIATION SPECTRUM - Google Patents

Description

Installation for determining the spectrum of electromagnetic radiation

The utility model relates to spectroscopy and can be used to study the spectral composition of electromagnetic radiation at wavelengths (frequencies), to find the spectral characteristics of emitters and objects interacting with radiation, as well as for spectral analysis

A known analogue using the principle of spectrally selective filtering. As a radiation detector, it uses a matrix photocell with an internal photoelectric effect, and the monochromator is a sealed chamber in which 4 echelettes are fixedly mounted. The light entering through the input window is successively reflected from them and monochromatized light exits from the exit slit. The chamber is connected to a pneumatic system, by means of which an increased or reduced gas pressure is created in it with high accuracy and stability. When the pressure of the gas filling the chamber changes, its refractive index changes, and a different spatial separation of the rays with different wavelengths is created. Due to this, a resolution of up to 5-10 Rev. is achieved. Sci. Instrum. 1990. Vol. 61. No. 10. P. 2546-2548.

The disadvantages of this device are the difficulty of maintaining a constant geometry of echelettes at boundary pressures, which requires the use of specific materials, and the technical complexity of holding with high accuracy pressures in a wide range, requiring the use of structurally complex and bulky additional equipment.

A known prototype that uses the principle of spectrally selective filtering, built according to a single-beam scheme and includes:

1) The radiation receiver is a photoelectron multiplier (PMT)

2) Primary collimator - a system of flat, spherical concave and convex cylindrical mirrors

3) Optical monochromator - a system of quartz prism from two concave echelettes of one plane and three concave mirrors.

4) The sources of radiation for the ultraviolet and visible regions are deuterium and halogen lamps, respectively.

5) Power sources for lamps and PMTs

6) PMT current meter - a current-to-voltage converter and a digital voltmeter with an accuracy of 0.00001 V

7) Control PC

The monochromator control mechanism is a PC-controlled system of four digital-to-analog converters, a precision servo motor, two stepper motors, two recoilless gears and an electronic echelette position indicator. A constant accelerating voltage (1000 V) from the source is supplied to the PMT, each lamp is powered from its source. The beam parallel to the light from the source after the collimator enters the monochromator through the diaphragm. Monochromatized light is directed to the entrance slit, passes through the sample under investigation, and passes through the exit slit to the PMT. The photocurrent signal from the PMT is converted to voltage and recorded by a digital voltmeter. The measured value is transmitted to the PC for registration. The device gives a spectral resolution of 0.1 nm at 250 nm. Applied Optics. 1992. Vol. 31. No. 10. P. 1557-1567.

The disadvantages of this device are high requirements for the accuracy of the manufacture of echelettes, mirrors, prisms, the positioning mechanism of the dispersing element and the resulting complexity of the design

The objective of the technical solution is to develop a compact and simple in design device for determining the spectrum of electromagnetic radiation with high resolution without the use of spectrally selective or spectral modulation filtering lasers with tunable frequency as monochromators and resonance detection methods.

A setup is proposed for determining the spectrum of electromagnetic radiation, which includes a photocell with an external photoelectric effect without secondary electron emission, two continuous-spectrum radiation sources for the ultraviolet and visible regions, a precision constant voltage source with voltage variation, a stabilized DC power supply, and a digital electrometer with sensitivity up to 10 A, casing shielding the photocell from external electromagnetic interference, primary collimator creating arallelny beam stabilized DC power supply for the radiation source, a personal computer for processing the measurement results and control the process. In this case, the positive pole of the voltage source is connected to the photocathode of the photocell, and the negative pole is connected to the anode. The studied sample is located immediately after the radiation source.

The operation of the proposed installation is based on the following principle:

An increase in the blocking voltage di leads to a decrease in the number of electrons that can leave the photocathode per unit time (photocurrent) with a constant emission spectrum, since the electric field energy of the cathode holding them in the material increases. In this case, the difference in the photocurrent forces (A1f) at the current (U) next (U + AU) voltage values is directly proportional to the radiation intensity in the frequency range from v to v + Av. This value corresponds to the difference in the integrated radiation intensities in the frequency range from UV to v and from UV. to у + Ду, where Уф is the frequency corresponding to the value of the blocking voltage by formula (1) at which photoemission of electrons from the photocathode is practically impossible, that is, the photocurrent strength is so small that it is not available for measurement, у is the frequency corresponding to voltage U, and АУ - the frequency range corresponding to the voltage step AU. When using this principle, the primary measured and determined quantities are related by the following relations

Ly Avikh + uh, (1)

Av / Lee e / h (2)

where - the frequency of the specified electromagnetic radiation, Hz,

and is the blocking voltage, B e is the charge of the eleron-ron, C h is the Planck constant, J / Hz ABY is the work function of the electron from the photocathode, J AU is the spectral resolution, Hz AU is the step of changing the blocking voltage, V

The installation diagram is shown in FIG. 1. Installation includes: 1 - two sources of a continuous spectrum, for the visible and ultraviolet regions (only one is shown in Fig. 1), 2 - a photocell with an external photoelectric effect without secondary electron emission, 3 - a collimator for directing a parallel radiation flux from the source to the studied sample, 4 - a precision source of constant voltage, with the possibility of voltage variation, 5 digital elerometer, 6 - a personal computer for processing measurement results and control the registration process, 7 - casing shielding PV, from internal current electromagnetic interference, 8 - stabilized DC power supply for the radiation source.

The proposed installation operates as follows: Diverging light from a radiation source (1) is converted by a primary collimator (3) into a parallel light beam and sent to the sample under study. The transmitted part of the world with the spectrum under study falls on the photocell (2) with an external photoelectric effect. A locking voltage (U) from a constant voltage source (4) is applied to the conclusions of the photocell from a precision constant voltage source, which varies in time with a constant or linearly increasing step. In this case, a photocurrent (1ph) arises in the photocell circuit, which monotonically decreases with increasing voltage. The current is measured by a digital electrometer (5) and the measurement results are transmitted to a PC (6) for processing. As a result, a working current-voltage characteristic (CVC) of the photocell is recorded on a PC. In the absence of the studied sample, the light enters directly onto the photocell and the control I – V characteristic is recorded. Subtraction from the working I – V characteristic of the control results in a corrected I – V characteristic corresponding to the spectrum under study and excludes spectral characteristics of the photocell and source

radiation and permanent components of the installation interference. Using the corrected CVC, the differential CVC is calculated (the dependence of A1ph / Au on U), from which the investigated spectrum of the radiation incident on the photocathode is reconstructed.

Thanks to the application of this principle and the exclusion of the optical-mechanical monochromator from the circuit, the design is greatly simplified, the dimensions are reduced and the spectral resolution of the installation is increased, compared with the prototype. For the proposed installation, as follows from formula (2), the spectral resolution (Av) is determined only by the step of changing the blocking voltage AU. So, at AU equal to 1 μV, the spectral resolution of the setup is 240 MHz, and the resolution is 4.4-10.

Claims (1)

Installation for determining the spectrum of electromagnetic radiation, including a photocell, two continuous-spectrum radiation sources for the ultraviolet and visible regions, a precision constant voltage source, a stabilized DC power supply for the radiation source, a precision direct current meter, a casing that shields the photocell from external electromagnetic interference , a primary collimator creating a parallel light beam, a personal computer for processing measurement results and control process, characterized in that a photocell with an external photoelectric effect without secondary electron emission was used, the sample under study was located immediately after the radiation source, a voltage-varying device was used as a voltage source, while the positive pole of the voltage source was connected to the photocell cathode, and the negative to the anode, a digital electrometer with a sensitivity of up to ^10-16 A. was used as a direct current meter.