High-precision spectral measurement
Schematic diagram of spectrum measurement (F:SSI OE300 1 optical chopper), G: grating spectrometer, B: photoelectric probe, D: Pr: Rb glass sample, C: sample box, E: tungsten bromide lamp source, H: computer, etc.
The light source emitted by tungsten bromide lamp is modulated by chopper OE300 1 and becomes light with certain frequency information, which becomes monochromatic light after passing through grating spectrometer. This monochromatic light hits the sample, and according to the structural characteristics of the sample, it will absorb the light with a specific wavelength, and then hit the probe B and convert it into an electrical signal. This weak electrical signal is detected by the lock-in amplifier.
TDLAS technology
Tunable diode laser absorption spectroscopy (TDLAS) technology is a detection technology that can measure the concentration, temperature field and even velocity field of gas components in industrial applications. TDLAS According to Bill-Lambert Law, when laser passes through gas molecular medium, as long as the wavelength of laser is equal to the energy level transition of any molecule, it will absorb some light. The relationship between the intensity of emergent light and the intensity of incident light is as follows:
Where is the absorption coefficient of the medium per unit length; Is the effective absorption length; Is the number of molecules per unit volume (i.e. concentration); Is the absorption cross section of the molecule, which is a Gaussian function of wavelength. After frequency modulation, and
As can be seen from the above formula, there are high-order absorption components in the absorption of laser by molecules. In the signal detection path, the second harmonic detection of the modulated signal is realized by phase detection at the frequency of 1f, 2f or 3f, and the first, second or third derivatives of the Gaussian function are obtained respectively.
In this kind of laser phase-locked system, the key part is to use the phase-locked amplifier to realize the bidirectional detection of the measured gas and the reference gas at the same time, and even to detect the measured gas, the reference gas and the laser background in three directions. The multi-channel harmonic measurement function of OE 1022 can solve this problem smoothly.
Quantum efficiency detection of solar cells
There are two kinds of quantum efficiency of solar cells.
External quantum efficiency (EQE): the ratio of the number of charge carriers in a solar cell to the number of photons with certain energy incident on the surface of the solar cell from the outside.
Internal quantum efficiency (IQE): the ratio of the number of charge carriers in a solar cell to the number of photons with certain energy that are not reflected by the solar cell and pass through the solar cell.
The quantum efficiency detection system of solar cells includes dual-channel lock-in amplifier, chopper and monochromator. The detection light emitted by the monochromator is divided into two beams, one of which is converted into photocurrent and input to the lock-in amplifier for comparison; The other path irradiates the solar cell, and the photocurrent generated by it is measured by the other path of the lock-in amplifier. The quantum efficiency of solar cells can be calculated by measuring the ratio of two channels and combining with related formulas.
Scanning tunneling spectroscopy
Scanning tunneling spectrum, that is, I-V or dI/dV-V test is done at a certain position on the surface of the sample, and the scanning tunneling spectrum with characteristic peaks is obtained. Under the characteristic peak voltage, the average current is kept constant, so that the needle tip is scanned in the X and Y planes, and the change of dI/dV with X and Y is measured, and the scanned tunnel spectrum image is obtained. The electronic and chemical properties of the surface are shown in I-V and dI/dV-V spectra.
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