Relationship Between Pulse Waveform Control of High Voltage Power Supply and Detection Range in Laser Radar
Laser radar, also known as lidar, has become an essential sensing technology for applications ranging from autonomous vehicles to atmospheric monitoring. The system transmits laser pulses and measures the time and intensity of returns from targets. The high voltage power supply that drives the laser transmitter determines the pulse characteristics, which directly affect the detection range and resolution.
Lidar systems operate by emitting short laser pulses and measuring the time for the pulse to travel to the target and return. The range to the target is calculated from the round trip time and the speed of light. The intensity of the return provides information about the target reflectivity. Multiple returns from a single pulse can reveal structure within the beam path, such as vegetation canopy and ground.
The laser transmitter requires a high voltage pulse to drive the laser diode or flash lamp. For laser diodes, the pulse current determines the optical power. For flash lamp pumped lasers, the pulse energy determines the optical pulse energy. The high voltage power supply must provide pulses with the required amplitude, duration, and repetition rate.
Detection range depends on the link budget, which accounts for all gains and losses in the optical path. The transmitted power is the starting point. The beam spreads as it propagates, reducing the power density. The target reflects a portion of the incident power back toward the receiver. The reflected power spreads as it returns. The receiver collects a fraction of the returned power with its aperture.
The transmitted power directly affects the detection range. Higher power enables detection of more distant or less reflective targets. The power is limited by eye safety regulations, laser damage thresholds, and power supply capabilities. The pulse waveform affects both the peak power and the energy, which have different effects on detection.
Peak power affects the signal to noise ratio for weak returns. The receiver noise includes thermal noise, shot noise, and background noise from ambient light. Higher peak power produces stronger signals relative to the noise, enabling detection of weaker returns. For photon counting receivers, higher peak power increases the photon count, improving the statistical accuracy.
Pulse duration affects the range resolution. Shorter pulses provide finer resolution, enabling discrimination of closely spaced targets. The range resolution is approximately half the pulse duration multiplied by the speed of light. However, shorter pulses require higher peak power to maintain the same energy, challenging the laser and power supply.
Pulse rise time affects the accuracy of range measurement. The leading edge of the return pulse is used for timing. A faster rise time provides a sharper timing reference, improving range accuracy. The rise time is limited by the laser response and the power supply switching speed.
Pulse repetition rate affects the data rate and the maximum unambiguous range. Higher repetition rates provide more data points per second, improving the angular resolution in scanning systems. However, the maximum unambiguous range is inversely related to the repetition rate. Returns from beyond the unambiguous range appear at incorrect ranges due to pulse ambiguity.
Pulse waveform control enables optimization for specific applications. For long range detection, maximizing pulse energy within safety limits is the priority. For high resolution mapping, minimizing pulse duration is the priority. For penetrating vegetation or seeing through obscurations, specific pulse shapes may enhance multi return detection. The power supply must support the required waveform control.
The high voltage power supply design must address multiple requirements. The output voltage must be controllable for power adjustment. The pulse timing must be precise for range accuracy. The pulse shape must be controllable for optimization. The repetition rate must be adjustable for different applications. The efficiency must be adequate for the power budget, particularly for mobile or airborne systems.
