Mod/demod method suitable for large caliber laser scintilloscope

Abstract

The invention discloses a modulation and demodulation technique applicable to a heavy caliber laser isotope scanner. The heavy caliber laser isotope scanner is equipment used for measuring the structure constant of the atmospheric refractive index. Digital logic devices are used to compose a multi-resonant trigger circuit to output square signals with an adjustable frequency and a duty factor to control a laser to send out high-frequency carrier laser. when the carrier signals are transmitted through atmospheric turbulence, the turbulence modulates the amplitude of the carrier signals; a modulated wave is received by a reflecting telescope and is converted by a photomultiplier; background stray light and other direct current noise components are filtered out via a catholic grounding power supply circuit and by coordinating with a capacitance coupling signal output circuit; subsequently output direct current amplitude-modulated signals without the background are outputted after being amplified by a transconductance amplifier (TIA); the signals are coupled to AC square signals of plus-minus symmetry by a capacitance; DC signals only including high frequency peaks are obtained via an absolute value detector; a low-pass filter circuit with a very small RC time constant to filter out the high frequency peaks to accomplish signals demodulation and obtain turbulence pulsating signals. The application of modulation and demodulation technique improves the signal to noise ratio of the heavy caliber laser isotope scanner and the capacity of resisting disturbance and measuring accuracy of the device; therefore, the performance of the device is more stable. The method is also applicable to other fields where photomultipliers are used for feeble signals detection.

Description

technical field [0001] The invention relates to the fields of atmospheric detection and photoelectric detection, in particular to a modulation and demodulation method of a large-aperture laser scintillator suitable for measuring the structural constant of the refractive index of the atmosphere. Background technique [0002] Atmospheric refractive index structure constant C n 2 It is a quantitative description of the intensity of optical turbulence and one of the most important parameters reflecting the optical characteristics of atmospheric turbulence. n 2 The optical measuring instrument, based on the aperture averaging effect of the flicker effect of light transmission, uses a laser point light source to emit, after atmospheric transmission, it is collected by the receiving telescope, and the path-averaged atmospheric refractive index structure constant is calculated according to the detected light intensity fluctuations. Since optical transmission experiments need to b...

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Problems solved by technology

In the experimental research and engineering application of laser atmospheric transmission, the commonly used methods to improve the signal-to-noise ratio are: use a narrow-band interference filter before the detector, and only the incident light in a small wavelength range near the central wavelength can pass through the filter. Light of other wavelengths is filtered out, but there is always radiation of the same wavelength as the signal light in nature, so for weak light detection, even if interference filters are used, a high signal-to-noise ratio cannot be obtained; a telescope is used as a receiver The device, placing the detector near the focal point, can improve the light collection ability on the one hand, and on the other hand, taking advantage of the relatively small field of view of the telescope, only the light parallel to the optical axis can reach the detector, and the rest of the light is absorbed by the inner wall of the lens barrel. Absorbed and unable to reach the detector, thereby improving the signal-to-noise ratio, but with the increase of the receiving aperture, the signal light is enhanced, and the incident background light is also increased; In the subsequent data processing, the background data is subtracted from the data including the signal and the background, and only the signal data is retained, thereby improving the measurement accuracy. However, due to the large difference in the background radiation between day and night, the instrument is required to have a wide dynamic linear range, which increases system design and Complexity of Mathematical Calculations

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