1. Lidar

1. Lasers used with lidar are pulse lasers which emit short laser pulses, different than continuous wave (CW) lasers which emit laser light continuously. Why are pulse lasers commonly used for lidar systems? In the lidar animation, what signal would be displayed on the screen of the oscilloscope when using a continuous wave laser?
   Answer: The return signal of a laser pulse is a time function where the time can be converted to distance. Continuous laser light does not induce a time function and hence distances cannot be retieved from such data.
2. Laser pulses are travelling with the speed of light c. Depending on the pulse length Δt they illuminate a certain distance range Δx=c·Δt along the direction of propagation. What should be the laser pulse length if the pulse shall illuminate a distance range of 0.5 m in air? Which range would be illuminated in water with the same pulse length?
   Answer:
   $\Delta t_{Luft}=\frac{\Delta x\cdot n_{Luft}}{c}\approx \frac{0.5\cdot 1.0}{3\cdot {10}^8}\approx 1.6\mathrm{n}\mathrm{s}$
   $\Delta t_{Wasser}=\frac{\Delta x\cdot n_{Wasser}}{c}\approx \frac{0.5\cdot 1.33}{3\cdot {10}^8}\approx 2.2\mathrm{n}\mathrm{s}$