Experimental Study on Km-Range Long-Distance Measurement Using Silicon Photomultiplier Sensor with Low Peak Power Laser Pulse  
[PERSON]  
1 Avionic Department, 5 th Main Maintenance Factory Directorate, Ankara 06990, Turkey;  
[EMAIL_ADDRESS] (C.C. ); [EMAIL_ADDRESS] (M.T.) [PERSON]  
2 Department of Advanced Technology, Graduate School of Natural and Applied Science, Gazi University, Ankara 06500, Turkey; [EMAIL_ADDRESS]  
[PERSON]  
3 Physics Department, Polatli Science and Letter Faculty, Ankara Haci Bayram Veli University, Polatli, Ankara 06570, Turkey 3* 3  
The cost and performance of Si-based systems make 0.9 \(\upmu\)m wavelength the preferred operation band for detectors. In ToF-based systems, the maximum range depends on many factors that include laser power, beam quality, Tx and Rx optics, detector choice, signal processing, etc. In such systems, the net effect is determined by the detection unit where all optical and electrical noise manifests itself as a signal to noise ratio (SNR). Noise in the photodetector is dominated by the readout electronics noise which can be eliminated by amplifying the current in the detector through the avalanche process. APDs with high internal gain are widely used for applications where high speed and low power detection are required such as visible light optical communications based on Si-APD [10] and laser rangefinders [11; 12]. In general, APD working in linear mode, that is biased below the breakdown voltage, requires large reverse bias of around 100-200 V in a Silicon APD which are characterized by their gain, quantum efficiency, excess noise, and bandwidth. Improvement in SNR is generally achieved by the process of avalanche multiplication of the photo-generated carriers. However, this multiplication process also creates excess noise in the APD as the gain increases. Therefore, fluctuations in the avalanche multiplication process, the excess noise, generated by the high reverse bias and temperature dependent gain limit the useful range of the gain. When APD is biased above breakdown voltage, it is working in the so-called Geiger mode which was introduced in 1989 [13]. In such a condition, the difference between bias voltage and breakdown voltage is called over-voltage. In this sense, single-photon avalanche diodes (SPAD) are APDs but designed to work above breakdown. The physical characteristics of SPADs are well defined in the literature [14; 15; 16; 17; 18]. SPAD arrays are also known as SiPMs which consist of microcell densities from a few hundreds to a few thousands per mm\({}^{2}\), depending on the size of the microcell. Due to its array structure, a SPAD has low fill factor and currently smaller active areas when compared to APDs. Moreover, because of quenching circuits they become blind (known as dead time) for a while (about 10's of nanoseconds) when the photon arrives. In ultra-low light applications especially, SPADs offer superior performance to the conventional APDs. In analog SiPMs, each SPAD is connected to its own passive quenching circuits. Naturally, one of the potential applications of SiPMs is the single photon detection for the purpose of photon counting, photon timing and photon imaging [17]. To our knowledge, long-range capability or test of SiPM with low energy laser in real environment is not reported in the literature. The existing studies [1; 2; 19] mainly cover the higher energy laser applications using SiPM. LiDAR has become an increasingly important technology not only in the areas of automotive, 3D-imaging and rangefinder application but also in the atmospheric sciences because of its ability to characterize the atmosphere. Laser light scattered by air molecules and aerosol particles that are suspended are detected by the receivers so that backscatter coefficient profiles can be determined. These aerosols are the indication of atmospheric pollution.