News Research

Saving lives by seeing through the smoke

When a building is on fire, every second counts. It can mean life or death for trapped victims and no emergency responder wants to be slowed down because they can’t see through walls of smoke. But firefighters can’t run headlong into every situation. When there’s a likelihood that toxic substances are present, they need to consult hazardous material databases, slowing them down, or rely on their own visual identification, which comes with human fallibilities. Victims’ lives and responders’ health are put at risk when this happens.

What is needed is an accurate, portable spectrometer that can identify toxic substances quickly and from safe distances. That is why researchers at TMOS are working on lightweight, portable spectrometers that could one day be integrated into firefighter’s body armour, much in the way that thermal cameras now are.

Every substance has its own unique thermal signature—the wavelengths at which it absorbs and emits photons. spectrometers can measure these thermal signatures to determine the chemical composition of something; this is how we know that the sun is made of hydrogen and helium, with smaller amounts of carbon, nitrogen and oxygen.

Traditionally, infrared spectroscopic instruments are limited to laboratory use due to their excessive size and fragile nature. Their operation often requires complex sub-sampling systems in air-conditioned shelters or lengthy fiberoptics. In addition, common environmental factors such as vibration, dust and temperature changes can have a detrimental impact on their performance. This makes them unsuitable for use in a field portable system such as mobile firefighting tool.

The University of Western Australia team is working to change this, having created tiny infrared spectral filters for remote thermal sensing and imaging  utilising microelectromechanical systems (MEMS). MEMS is set to disrupt the current spectroscopic industry with its small size, lightweight, minimal power requirements and robust construction, enabling spectroscopy applications never before imagined.

Chief Investigator Marius Martyniuk says, “These miniaturised on-chip lightweight and small size devices are being seen as futuristic solutions towards simple and low-cost miniature spectroscopic remote systems operating in the very important thermal infrared emission band of the electromagnetic spectrum, where minimising weight, size and power requirements is of most critical importance, such as on firefighter headsets.

Lead author Gurpreet Singh Gill says, “We have designed and built an electrically tunable surface micromachined Fabry-Perot filter using Ge and BaF2 optical layers — the first time this has been successfully manufactured utilising low-index BaF2 thin-films. This filter could one day be integrated into thermal cameras on a firefighter’s headset, enabling immediate identification of toxic substances, giving firefighters the ability to move quickly and safely.” 

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Large-area narrowband Fabry–Pérot interferometers for long-wavelength infrared spectral sensing

Journal of Optical Microsystems, 19 May 2022

Gurpreet Singh Gill, Michal Zawierta, Dhirendra Kumar Tripathi, Adrian Keating, Gino Putrino, Konkaduwa Kamala Mesthrige Buddhika Dilusha Silva, Lorenzo Faraone, Mariusz Martyniuk

This paper presents a proof-of-concept for microelectromechanical system (MEMS)-based fixed cavity Fabry–Pérot interferometers (FPIs) operating in the long-wavelength infrared (LWIR, 8 to 12  μm) region. This work reports for the first time on the use of low-index BaF2 thin films in combination with Ge high-index thin films for such applications. Extremely flat and stress-free ∼3-μm-thick free-standing distributed Bragg reflectors (DBRs) are also presented in this article, which were realized using thick lift-off of a trilayer structure fabricated using Ge and BaF2 optical layers. A peak-to-peak flatness was achieved for free-standing surface micromachined structures within the range of 10 to 20 nm across large spatial dimensions of several hundred micrometers. Finally, the optical characteristics of narrowband LWIR fixed cavity FPIs are also presented with a view toward the future realization of tunable wavelength MEMS-based spectrometers for spectral sensing. The measured optical characteristics of released FPIs agree with the modeled optical response after taking into consideration the fabrication-induced imperfections in the free-standing top DBR such as an average tilt of 15 nm and surface roughness of 25 nm. The fabricated FPIs are shown to have a linewidth of ∼110  nm and a suitable peak transmittance value of ∼50  % , which meets the requirements for their utilization in tunable MEMS-based LWIR spectroscopic sensing and imaging applications requiring spectral discrimination with narrow linewidth.