What is Lidar and How Does It Work?

History

In 1960, Theodore H. Maiman announced the build of a red coherent light pushed from a ruby crystal, which was the first laser. Nearly 30 years later in 1989, the first law enforcement speed measurement laser device was patented. 

Lidar & Laser

Lidar is an acronym. It stands for “light detection and ranging.” Laser is also an acronym, standing for “light amplification by Stimulated Emission of Radiation. Lidar devices are designed to measure speed through energy produced through a laser device. The term lidar is used when describing a device used for down the road speed measurement, currently only designed for stationary use. 

The science

The technology behind the laser is fairly complicated. When put in its most simple form, laser energy is created by energizing a lassing medium, a piece of active material, which has been placed in a sandwich between mirrors. 

The atoms of the medium are placed into an excited state from an outside energy source. They store some of this energy, which allows them to release some of their already stored energy. This releases as light energy, resulting in amplification of incoming light. 

The two mirrors are placed at an exact distance apart from one another. This creates a standing wave bouncing back and forth from one mirror to the other. This allows the light waves to become lined up with one another. One of the mirrors is designed to allow some of this light to escape, and pass through as a laser beam. 

Lasers can be produced from several different active materials. Some examples of different types of lasers include the semiconductor, gas, chemical, excimer, and free electron. There are also many different types of optical resonator devices. Some of the typical ones include:

• Semi-Conductor Lasers – unlimited uses in high technology applications such as fiber optics and laser devices
• Gas Lasers – popular applications include the entertainment industry, light shows and movies.
• Chemical Lasers – used for internal confinement and military applications
• Excimer Laser – used in the medical field for surgical procedures
• Free Electron Laser – develop powerful light sources for defense, industry and research

How does it work?

The lidar employs a “time of flight” method to measure the speed of the desired vehicle. It does this by shooting out a short burst of lasers at the vehicle, all measuring the range of the vehicle from the lidar. The device then adds these measurements together, seeing how fast the vehicle was either getting closer or moving further away, calculating speed. Think of this as a basic math problem in high school: speed = distance/time. If the driver is moving away from the operator it presents the speed value as a negative, and if the driver is moving towards the operator it is presented as a positive value. 

The lidar carries three distinguishable characteristics similar to those of other forms of electromagnetic energy. These are:

• Signal speed – Lidar lasers travel at the speed of light, which is generally accepted to be 186,282 miles per second. 
• Wavelength – “The distance between two points in a periodic wave that have the same phase.” The wavelength of a lidar is about 904-905 nanometers.
• Frequency – A measurement of cycles per second. The frequency of lidar is about 330 terahertz.

Lidar also carries the same behaviors as other forms of electromagnetic energy, meaning that it can be reflected, refracted, or absorbed. 

It is important to understand how lidar works, and understand your rights that go along with it. Do not allow a false allegation to harm your driving record, cost you money, or even place you in prison. Speeding violations are all viable to be taken to court in Vermont at the discretion of the alleged violator, who stands to gain from having the punishment reduced or revoked and challenging the accuracy of the Lidar is one such strategy to attack the validity of the State’s case.