Industrial Electronics

7 key parameters for specifying laser systems and components

27 January 2021
Lasers are finding an increasing use in numerous applications including communications and transportation. Source: AdobeStock

Lasers, also known as light amplification by stimulated emission of radiation, are finding ever-increasing applications. They are used for communication, holography, laser pointers, metalworking and target acquisition in military applications.

While there exists a vast range of laser systems, these systems share common terminology, parameters and data. Understanding these parameters is crucial for correctly specifying and calculating laser systems and components to meet specific application needs.

This article covers seven key parameters for specifying laser systems.

Wavelength

Wavelength describes the spatial frequency of the light wave emitted by the laser, and it is measured in nanometers (nm). Different lasers operate at different wavelengths, from ultraviolet to infrared.

Lasers are classified primarily according to the lasing medium. The table below describes the various types of materials used for lasing and the wavelengths that are emitted by each type of laser.

Laser types and their wavelengths. Laser types and their wavelengths.

Shorter wavelength lasers, such as the Argon Fluoride laser, are suitable for micromachining applications. In contrast, the intermediate or long-wavelength lasers are suitable for laser cutting and welding.

Power and energy

The power of a laser refers to the optical power output of the laser beam. In simpler terms, it is the continuous power output of a continuous wave laser and the average power of a modulated or pulsed laser.

The pulse energy of a pulsed laser is simply the total optical energy of the pulse. It is directly proportional to the average power of the laser and inversely proportional to the laser’s pulse repetition rate. It is given as:

Beam diameter and focal spot size

The laser’s beam diameter refers to the diameter of the laser beam at the exit face of the laser housing. Because the boundary of arbitrary optical beams is not clearly defined, its diameter cannot be measured like regular cylindrical objects. The beam diameter is often defined as the width at which the beam’s intensity is 0.135 times the maximum value.

The focal spot size of a laser beam describes the beam diameter at the focal point of the lens system. It is given as:

Where:

  • wf = laser spot size
  • wo = laser’s beam waist (the region where the beam diameter reaches its minimum value)
  • f = focal length
  • l = laser’s wavelength

Consider a Gaussian beam with a lens of focal length f, as shown in Figure 2. The laser spot size is wf.

A larger beam diameter translates to a higher cost of the laser due to the need for larger optics. In contrast, a lesser beam diameter causes an increase in power density.

Power density

Laser power density is the energy or optical power that is delivered per region or active area. It is typically measured in W/cm2 or J/cm2, and it shares an inverse relationship with the beam diameter.

The higher the power density, the more likely the occurrence of laser-induced damages. As such, high power densities are suited for external applications like welding and laser cutting, while low power densities are suitable for medical applications and scientific research.

Divergence

Beam divergence is the angular measure of how the beam diameter increases with the distance from the laser aperture. Although laser beams are often assumed to be collimated, there is always some form of changes to the beam radius, especially within long propagation distances.

The divergence of a Gaussian beam is measured in mrad and defined as:

Where:

  • q = angular divergence
  • l = laser’s wavelength
  • wo = laser’s beam waist (the region where the beam diameter reaches its minimum value)

Note that the angular divergence (q) is a far-field approximation. As such, it does not accurately represent the beam divergence in regions close to the beam waist. Instead, these approximations are more accurate as the distance from the beam waist increases.

Working distance

The working distance of a laser system describes the distance from the front-most edge of the focusing lens to the surface the laser is focusing onto. Laser systems used in medical laboratories often operate with a small working distance, whereas applications like remote sensing and metalworking often seek to maximize working distance.

Laser safety class

Lasers are classified based on their potential for causing eye damage or other injuries. FDA Center for Devices and Radiological Health (CDRH) recommends that laser products employ the applicable warning labels based on the laser classes present.

Laser classes with applicable warning labels.Laser classes with applicable warning labels.

Laser system selection is a tedious process. Incomplete or inaccurate specifications cause errors in the integration of laser products. Engineers need to be informed about these parameters to ensure that the laser system is delivering what it is expected to deliver. These calculations and equations should help.

To contact the author of this article, email engineering360editors@globalspec.com


Powered by CR4, the Engineering Community

Discussion – 1 comment

By posting a comment you confirm that you have read and accept our Posting Rules and Terms of Use.
Re: 7 key parameters for specifying laser systems and components
#1
2021-Feb-24 8:55 AM

Very interesting to know the key parameters to specify a laser system for a specific application. I think first it is important to fix the application and then to choose the laser system.

Nowadays, there are many types of lasers, their specifications are given to meet your applications.

In the case of femtosecond laser as an example the main parameters are:

  • Wavelength λ
  • Repetition rate fp
  • pulse duration τ
  • Pulse energy Ep
  • Beam quality Qb
Engineering Newsletter Signup
Get the Engineering360
Stay up to date on:
Features the top stories, latest news, charts, insights and more on the end-to-end electronics value chain.
Advertisement
Weekly Newsletter
Get news, research, and analysis
on the Electronics industry in your
inbox every week - for FREE
Sign up for our FREE eNewsletter
Advertisement
Find Free Electronics Datasheets
Advertisement