Technical Article

Lasers and Their Uses in Sensing and Object Detecting

March 30, 2023 by Antonio Armenta

A subset of light is the focused cohesive beams that make up lasers, which can be used in optical sensing. These devices provide benefits of greater range, precision, and even mapping for mobile robotics.

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Laser sensors are a special kind of optical sensor. A laser is a very narrow beam of light of a single color with the same frequency that travels in the same direction. The word laser stands for Light Amplification by Stimulated Emission of Radiation.

The first laser was invented in 1960 by Theodore Maiman. Since then, laser devices have found numerous applications in multiple industries. Some commercial applications of lasers include laser surgery and skin treatments, weapons and military target markings, printers, and even DNA sequencing instrumentation.


laser weapon system from Lockheed Martin

Figure 1. A laser weapon system from Lockheed Martin. Image used courtesy of Lockheed Martin


Lasers are also very popular in the manufacturing sector, providing high levels of precision in multiple processes. The following sections will review some of the most popular industrial laser devices and the operating principles of laser devices.


How Do Lasers Work?

Three main components comprise a basic laser device: the source, the gain medium, and the optical resonator.


Laser Sources

Lasers operate with light beams as a source. The source material can be an electric current, a laser diode, a flashlamp, microwaves, solar radiation, a chemical reaction, or another laser. All of these source materials must have coherence as a common feature. Coherence means that light travels in the same direction.

Semiconductor laser diodes or Laser LEDs are the most popular source material for devices used in industrial automation. Some types of laser diodes include the Fabry–Pérot laser, the single longitudinal mode (SLM) laser, the distributed feedback (DFB) laser, and the vertical-cavity surface-emitting laser (VCSEL). 


Fabry-Perot laser diode

Figure 2. A Fabry–Pérot laser diode. Image used courtesy of RP Photonics


The Fabry–Pérot laser emits light at various wavelengths and can produce high-power output. It is also relatively cost-effective. SLM lasers are an improvement over Fabry–Pérot ones in terms of output power, but they work on a single-frequency component. They are used for radar detection and composition measurement, to name a few.

DFB lasers offer better stability than their counterparts and are widely used in high-speed fiber optic applications. VCSEL is the newest laser source technology from the group. VCSEL has quickly established itself as the best choice for short-distance applications due to its uniformity, resistance to high temperatures, and lower manufacturing costs.


Light Amplification and Gain Medium

Lasers are classified according to their gain medium. The gain medium defines the material used to amplify the light source. The most recognizable gain mediums include semiconductors, liquid, solid-state, gas, and fiber. 

Semiconductor lasers employ the Laser LEDs described before. In liquid lasers, liquid dye molecules dissolved in a solution help radiate the energy from the source. They are more popular in medicine. 


array of solid-state lasers

Figure 3. An array of solid-state lasers. Image used courtesy of Passat


Solid-state lasers use highly reflective glass mixed with rare elements such as chromium, erbium, neodymium, or ytterbium to achieve optical gain. They are the most popular medium in LiDAR lasers. 

In a gas laser, an electric current is converted to a light output when passing through a gas medium. Popular gasses include carbon dioxide (CO2), helium, and argon. Finally, fiber lasers are highly precise and based on fiber optics technology.


Optical Resonator

This is the last step before the laser beam is output from the device. The resonator consists of a pair of mirrors that surround the medium. The purpose of the resonator is to help build up the energy of the light beam by reflecting light back and forth through the medium several times.


optical resonator example

Figure 4. An example of an optical resonator. Image used courtesy of Wikimedia Commons


Laser systems base their measurement principle on a triangulation method. First, the laser beam is amplified by the medium, and the resonator exits the sensor device and travels until it hits the surface of an external object. Then, the reflected light beam bounces back to the sensor and is received by a specialized laser-receiving component. Triangulation is achieved because the receiving element can calculate the reflected beam's entry angle and displacement. 


Laser Sensor Types

Some of the most common laser sensors include:

  • Distance sensors

  • Proximity sensors

  • Laser curtains

  • Positioning Lasers

  • Edge detection sensors

point cloud generated by a 3D LiDAR on an autonomous vehicle

Figure 5. A point cloud generated by a 3D LiDAR on an autonomous vehicle. Image used courtesy of Velodyne Lidar


LiDAR Sensors

Light Detection and Ranging (LiDAR) sensor technology deserves a special section. It calculates the time it takes for a laser beam to be reflected back to the source. LiDAR is experiencing tremendous growth in the automation business with applications ranging from autonomous cars to smartphones.

This operation occurs at very high speeds of up to 900 rpm for rotating lasers. The light beam can measure the distance to any surface, generating a "point cloud." A point cloud is a collection of many cloud points that provide precise shape and distance information.

Due to the high data requirements, LiDARs are usually coupled with their computer processors.

LiDARs used in industrial automation are mostly bidimensional, rotating the laser on a single plane. However, more complex technologies, such as autonomous cars, require more information about the surroundings and therefore integrate 3D LiDARs.


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