Introduction
to Laser Radar
Introduction
to Laser Radar
Laser radars, also referred to as ladar or lidar, use pulsed infrared laser light (invisible to the eye) instead of continuous microwaves to detect targets. Lasers are extremely pure (coherent) lightwaves, similar to only one (pure) color of light. Note that white light consists of multiple wavelengths (colors) with random (non-coherent) phases. Theodore Maiman of Hughes Aircraft Company (California) built the first working laser using a ruby rod pumped by a flash lamp in May of 1960. Police traffic laser radars use solid-state diodes to generate laser light.
| LASER | - | Light Amplification by Stimulated Emissions of Radiation | |
| LADAR | - | LAser Detection And Ranging | |
| LIDAR | - | LIght Detection And Ranging | |
| RADAR | - | RAdio Detection And Ranging |
Laser radars transmit pulsed infrared laser light to measure target range. The time it takes for a pulse to travel (at the speed of light) from the ladar to the target and back is used to compute range. The change in range over time is used to calculate speed. Laser radars typically (depending on model) required 0.3 to 0.7 seconds to get one speed reading. Typically tens to hundreds of pulses are used to calculate one speed reading.Laser radar apertures (light antennas) are optical focusing devices (lenses, prisms, and/or mirrors) used to collimate laser energy into a narrow beam. Some models use the same aperture for transmit and receive; some use separate apertures (one for transmit and one for receive). Some multiple apertures are side-by-side, others on one on top of the other (usually top transmits).
Laser radars use a semiconductor diode (typically 3 diodes) to generate infrared laser light. Police light radars emit infrared laser energy around 904 nm wavelength (in the infrared band). While the transmit pulse is relatively narrow, on the order of nanometers (nm), detectors can react to wavelengths on the order of 10's to 100's or more nanometers.
Laser radars operate from a stationary position only (no moving mode) and measure speed of approaching traffic, receding traffic, or both directions. Most lidars indicated traffic direction being measured , typically a plus (+) indicates approaching traffic and a minus (-) indicates receding traffic. Besides displaying speed and direction, most models also display range. Most models also have a range only mode, for measuring the range of objects.
Government Regulations
The FCC regulates radiated emissions from high speed circuits such as processing circuits inside a lidar, but not light frequencies (wavelengths). The Federal Drug Administration (FDA) Center for Devices and Radiological Health (CDRH) regulates laser products sold in the United States. Police laser radars are Class 1 devices (by American National Standards Institute definition) and considered eye-safe based on current medical knowledge -- even so it is probability a good idea NOT to stare (or look) at a laser aperture while transmitting, especially on/in beam at close range.
