A lidar based on UV laser is developed to observe air quality in Beijing. The initial laser wavelength is 1064 nm, and an emission wavelength of 355 nm is obtained after the second-harmonic generation and third-harmonic generation. The output energy is 30 mJ/pulse, and the pulse width is 7 ns. Echo signals are collected by a 304.8 mm diameter Newtonian telescope. With high-power ultraviolet laser excitation, the intensity of atmospheric pollutants is studied by the laserinduced fluorescence (LIF). The Mie scattering is detected simultaneously and both signals are detected by the photomultiplier tubes (PMT). The system is calibrated by a series of experiments. The aerosol extinction coefficient retrieved by Mie signal from this system agrees well with that from another lidar with a laser wavelength of 532 nm. The fluorescence efficiency of atmospheric pollutants are obtained by calculating the fluorescence-to-Mie ratio (FMR). The time and spatial resolution of the system are 5 s and 7.5 m, respectively. The continuous change of air quality over a period of time is studied by the mean value of FMR. Many observations are carried out under different air quality conditions, and the experimental results are in good agreement with the results of the ground observation station. In summary, this method based on UV laser is feasible in the field of atmospheric remote sensing and have potential applications in the field of air quality monitoring.
We have designed and demonstrated an all-fiber laser which can switch the operation mode between the pulsed mode and the continuous mode. Under the pulsed operation mode, the maximum output pulse energy is measured to be 120 μJ with a pulse width of 400 ns. The pulse width is continuously adjustable between 100 ns and 600 ns. Under continuous operation mode, the maximum output power is 2 W. Switching between these two operation modes can be done with simple instructions within several milliseconds. Large-mode-area (LMA) fiber amplifiers are adopted to support the high peak power. The LMA fiber amplifiers are coiled in a circle with a diameter of 25 cm and the high order transverse mode are suppressed by the bending loss. The M squared factors of the designed laser are 1.204 on x-axis and 1.293 on y-axis. This laser is optimized for coherent Doppler lidar system that can detect at both the near (within several tens of meters) and far distance (more than a dozen kilometers).
In this paper, the laser-induced fluorescence (LIF) technology is utilized for rapid assessment of the purity of quartz glass, especially for the screening of high-purity quartz glass. A 355 nm laser was applied as excitation source to induce the fluorescence signal of the quartz glass samples. The fluorescence signal is then transmitted to the spectrometer through an optical fiber for spectral acquisition. Because only the impurities in quartz glass induce fluorescence, purity quartz glasses does not have a distinct fluorescence signals or fluorescence peaks. The purity evaluation of high-purity quartz glass can be achieved by analyzing the obtained signals. The standard deviation and the ratio of the maximum to minimum values of the signals were calculated to indicate the intensity of the fluorescent peak of the signal. The thresholds were then set to distinguish between high-purity and low-purity quartz glasses. The method has the advantages of high speed, high precision and high reliability, and is of great significance for the rapid screening of quartz glass with high purity requirements.
Compared to scanner imaging ladar, non-scanning LADAR plays a more prominent role in the militarily imaging
scenarios. Non-scanning LADAR has many advantages, such as structure simplicity, high reliability, imaging efficiency
and etc. However the range accuracy is low. This paper proposes a technique to use a designed delay line module in the
APD array LADAR systems, which could significantly improve the range accuracy in all channels. A semiconductor
laser is used as light source. A 5×5 APD array detector is adopted as the sensitive unit. A 25 channel parallel amplifier
circuit is designed to process the signal with bandwidth 240 MHz . Field Programmable Gate Array (FPGA) is used to
process these 25 signals paralleled, with a delay line module designed, to significant improve the ranging accuracy .The
clock frequency of FPGA is 400MHz with accuracy 2.5ns. The delay lines module are used to measure part of pulse
flying time, which is shorter than the clock cycle and could not be directly measured by the clock, and that is the cause of
the ranging accuracy. Every delay cell is 46picoseconds , total timing accuracy is less than 500picoseconds. By using
above technique, a short distance imaging experiment is presented and get the 5 ×5 pixels range image. The result is
analyzed together with the factors, which influence the accuracy of ranging image, it shows the ranging accuracy of each
pixel is 10cm. And some advanced methods are proposed to improve the accuracy of the system in the future.
KEYWORDS: Signal to noise ratio, LIDAR, Sensors, Semiconductor lasers, Amplifiers, Avalanche photodetectors, Signal detection, Target detection, Photodetectors, 3D acquisition
Active multi-spectral detection technology is used to acquire the information of the targets,such as spectrum, distance,
intensity, and location and so on. So the active multi-spectral detection technology becomes one of the main trends of
development of detection system in the future. Based on the analyzing the theory of streak tube lidar active multi-spectral
detection system, we design a wavelength conversion circuit which can be applied to implement wavelength conversion
in the streak tube lidar in the active multi-spectral detection. Through the O-E-O conversion mode, the wavelength of
laser echo signal which contains the target information is transformed into another wavelength which represents the
spectral peak response wavelength of the stripe tube photocathode. The simulation results show that when the input laser
echo signal wavelength is 1.55um, and the after-converted wavelength is 0.85um , the photon conversion efficiency can
reach 2.2×106 ,the signal to noise ratio can reach 19.3dB. And when the target distance or the signal bandwidth
increases, the signal to noise ratio(SNR) will decrease accordingly.
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