## 2 Experimental Studies  
The MICRORB\(-\)SMTPA\(-\)10020 pin adapter board made by SensL, was used in the receiver. Some important parameters for the SiPM detector used in this work are summarized in the Table 1. The printed circuit board (PCB) board houses the SiPM sensor and has through-hole pins to allow its use with standard sockets or probe clips [33]. This sensor was mounted to our designed amplifiers on the PCB board, forming a SiPM-based Rx for our experiments as shown in Figure 1. In the experiment, the optimum overvoltage in terms of gain and noise level is determined to be 10 Volt, and it remained fixed during the experiments. Therefore, the typical operating (bias) voltage is \(-33\), see Table 1. In this work, we used a standard output signal which was connected to the amplifier circuit. The fast output was also utilized in order to provide information on the number of photons detected. Although fast output gives much better accuracy of the target on ranging, we consider that fast output signal is difficult to handle in readout electronics since it has both positive and negative sides. The laser used in this work was the OSRAM SPL PL90-3, operating at a wavelength of 905 nm and providing up to 90 W of peak power. Beam divergences parallel and perpen \begin{table}
\begin{tabular}{l l} \hline \hline
**Parameters** & **SiPM (MICRORB\(-\)SMTPA\(-\)10020)** \\ \hline Microcell Size & 20 \(\upmu\)m \(\times\) 20 \(\upmu\)m \\ \hline Active Area & 1 mm \(\times\) 1 mm \\ \hline Number of Microcells & 1590 \\ \hline Microcell Fill Factor & 63\% \\ \hline Breakdown Voltage & 23 Volt \\ \hline Typical over-voltage & 10 Volt \\ \hline Photon Detection Efficiency at 905 nm & 5.6\% \\ \hline Responsivity at 905 nm at typical overvoltage & 61 kA/W \\ \hline Gain & 0.9 \(\times\) 10\({}^{6}\) \\ \hline Dark Count Rate & 2.7 MHz \\ \hline Dark Current & 0.54 \(\upmu\)A \\ \hline Rise Time\(-\)Standard Output & 1 ns \\ \hline \hline \end{tabular}
\end{table} 
Table 1: SiPM parameters from the reference [35]. Figure 1: Picture of silicon photomultiplier (SiPM) on printed circuit board (PCB) board with amplifiers. dicular to the axis of propagation were 9 and 25 degrees, respectively. The driver board of the laser was designed by us that consists of a Gallium Nitride field-effect transistors for high-speed switching and discharging capacitors to supply necessary large pulse current. Measured energy at the output of the laser diode is approximately 9 uj at 100 ns pulse width and 1 kHz repetition rate. Note that at the output of the laser rangefinder we lose almost 70% of it because of the large divergence of the laser diode which overfills the aperture. The experiment was performed by using our own prototype shown on the left side of Figure 2 and on the right is the representation of the setup. Both detector (SiPM) and laser were mounted to the platform which can be slightly adjusted for alignment. The Tx and Rx unit both had the same high precision aspheric lens with a focal length of 100 mm (AL50100-B, Thorlabs, Newton, NJ, USA) and its design wavelength was 780 nm. These lenses which have anti-reflection coating between 650 nm and 1050 nm are 50 mm in diameter with an f-number of 2. They are mounted such that their plain sides facing the laser and detector. Collimated laser beam is in line-rectangular shape and its long edge divergence is approximately 3 mrad (full angle). Receiver full angle field of view (FOV) is calculated as 10 mrad. When we consider the single pixel size, then we obtain instantaneous FOV of 0.2 mrad which corresponds to 20 cm \(\times\) 20 cm area at 1 km distance for single pixel. In one of our measurement, we used a black wooden target of size 2 by 2 m. The measured distance for this target was 1880 m. Laser spot size on this target was about 5.5 m when the full angle divergence was taken. However, angular field of view of the receiver was 18 m which is larger than the target and the laser spot. In this case the background noise increased which degraded the SNR.