Identifying Harmful Infrared Beams in Laser Rooms with FLIR Thermal Imaging Cameras

Table of Content

Introduction
Ensuring Researcher Safety
Visualizing Invisible Infrared Beams
Aligning Optical Equipment
Finding Explosives or Drugs
Conclusion

Introduction

Invisible infrared beams produced by some lasers may create a fire or harm to users, and therefore, a high level of care must be taken while operating lasers to avoid such risks. The FLIR i7 thermal imaging camera used by researchers at the laser room of the University of Glasgow helps them to safely operate their terahertz laser research setup (Figure 1).

Figure 1. In the laser room of the University of Glasgow researchers use a FLIR i7 thermal imaging camera to ensure their own safety when they work with their terahertz laser research setup.

The laser systems in our lab generate invisible high power infrared laser radiation. I probably do not need to explain that these invisible beams might be dangerous to the researchers. We wear goggles to prevent damage to our eyes, but if the invisible beam would hit our clothing or skin it might cause serious accidents. That’s why we need safety equipment in order to spot these invisible beams, which is where the FLIR thermal imaging camera comes into play.

Yong Ma, Research Assistant at the Microsystem Technology Group , School of Engineering, at the University of Glasgow

The FLIR thermal imaging camera is used for this purpose in the lab.

Ensuring Researcher Safety

Before I start to work with our terahertz laser research setup I always scan the entire area with the FLIR i7 thermal imaging camera to detect infrared laser beams that are projected in the wrong direction, to make sure that it is safe. But that is not the only application I use it for. I also use it to monitor overheating electrical equipment and gas valves, tubes and tanks.

Yong Ma, Research Assistant at the Microsystem Technology Group , School of Engineering, at the University of Glasgow

Figure 2. By visualizing the heat from invisible infrared laser beams the FLIR i7 helps to guarantee the researchers' safety.

The invisible terahertz laser beam is produced in a two-step process.

The first step is the CO2 mid-infrared laser system. This produces an infrared laser beam of 50 Watt at a wavelength frequency of 10.6 micrometer. This regular infrared laser beam is transformed into a terahertz laser beam by channeling it through pressured methanol. The resulting terahertz laser has a power of 150 milli-watt and a wavelength frequency of 119 micrometer.

Visualizing Invisible Infrared Beams

According to safety procedures, the terahertz infrared laser beam generated is a Class IV laser, and thus, needs goggles for operator safety. Therefore, it is necessary to have the capability to see the invisible laser to avoid safety issues in the research setup.

We use the FLIR i7 thermal imaging camera for this purpose because it has a good balance in affordability and performance. The microbolometer detector of the FLIR i7 thermal imaging camera is not especially designed to detect infrared radiation in the terahertz wavelength frequency. The terahertz laser produces infrared beams at a wavelength frequency of 119 micrometer while the FLIR i7 thermal imaging camera has a spectral range of 7.5 to 13 micrometer.

This means that the FLIR i7 thermal imaging camera does not detect the beam directly. But if the infrared beam produced by the terahertz laser hits an object or surface it will cause it to heat up. This rise in temperature can quite easily be detected using the FLIR i7 thermal imaging camera. It is that principle that I use to make sure there are no stray infrared beams leaking from the setup.

Figure 3. The heat from invisible infrared laser beams clearly shows up in the thermal images.

Aligning Optical Equipment

The invisible terahertz beam is channeled towards specific targets using various infrared lenses and mirrors. However, it is a challenging task to aim an invisible laser beam, which is where the FLIR i7 thermal imaging camera can be effective, explained Ma.

Before I had the FLIR i7 thermal imaging camera I used thermal paper, which discolors when it becomes warm, to detect the terahertz infrared beam and align the optical components, but this method is inaccurate and slow. With the FLIR i7 thermal imaging camera I can much more accurately detect the infrared beam and align the optical components of the setup.

Figure 4. Using the FLIR i7 thermal imaging camera Ma aligns the optics in his research setup.

Ma said the research project is aimed at devising a terahertz imaging system with a potential for use in a myriad of applications.

The terahertz region of the electromagnetic spectrum sits between the microwave and the mid infrared region, which is usually defined by the frequency range of 0.1 − 10 THz. It is one of the least explored ranges of the electromagnetic spectrum, but it shows great potential for applications in the fields of science, security and medicine.

“Terahertz infrared radiation penetrates farther in most materials than other types of infrared radiation. It can penetrate many dielectric materials, such as clothes, paper boxes, plastic bags and even human tissue. But even though it penetrates  deeply in the human body it is a non-ionizing type of radiation and is therefore safer to use in medical scans than conventional methods such as x-ray and ultrasound.

Ma sees a number of potential applications for the terahertz radiation. The non-invasive nature makes it ideal for medical purposes. However, it can also be used in the fields of high speed communications, security, and spectroscopic analysis. Novel chemical and biochemical information can be acquired with terahertz spectroscopy. The lesion location of certain kinds of disease like skin cancer can be determined in a non- invasive manner by scanning with terahertz infrared imaging, said Ma.

Finding Explosives or Drugs

It might also be used to enhance security checks at airports. Terahertz imaging can be used to see hidden objects under clothes, paper boxes and plastics bags, such as explosives or weapons. Many chemical or biological materials such as explosives or illegal drugs have characteristic fingerprint spectral absorption in the terahertz region. Therefore we can identify explosives or illegal drugs with help of their THz spectral
fingerprints. Terahertz communications systems have the potential to provide a much broader bandwidth, more directional transmission, which is useful to reduce the size of the antenna, and more secure information communication due to the short transmission distance.

Conclusion

Terahertz imaging has not been explored in detail when compared to other forms of electromagnetic radiation. The terahertz research work aims at system integration and fabricating terahertz optical components. The research is focused on delivering an affordable and high-performance terahertz imaging system for security and medical purposes. This task can be safely and accurately carried out with the help of the FLIR i7 thermal imaging camera.

This information has been sourced, reviewed and adapted from materials provided by FLIR Commercial Systems.

For more information on this source, please visit FLIR Commercial Systems.

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