Mid-infrared light is a type of electromagnetic radiation that is invisible to the naked eye. It has significant applications in various fields, such as medicine, security, and environmental monitoring. However, detecting mid-infrared light has been challenging because it requires bulky and expensive tools and must also be done at very low temperatures.
What is Mid-Infrared Light?
Infrared light is a component of the electromagnetic spectrum that lies just beyond the visible light. This light is invisible to the human eye since it has wavelengths longer than red light.
Infrared is divided into three categories based on wavelength: near-infrared, mid-infrared, and far infrared. Near infrared is the closest to red light among these three divisions, while far infrared is further. They are separated into distinct regions based on the frequency of the infrared radiation relative to the visible spectrum.
Mid-infrared light is characterized by wavelengths that range from 2.5 to 25 micrometers. Since it has longer wavelengths than near infrared, it can penetrate the body more deeply and reach the soft tissue. Generally, mid-infrared light helps the human body by expanding the blood vessels and increasing local circulation.
Making the Invisible, Visible
Using quantum systems, researchers from the University of Birmingham and the University of Cambridge have developed a novel method that can detect mid-infrared (MIR) light at room temperature. The study was carried out at the Cavendish Laboratory and marks an important milestone in gaining insight into the mechanisms of chemical and biological molecules.
In this experiment, the researchers converted low-energy MIR photons into high-energy visible photons using molecular emitters. This innovation enables scientists to detect MIR and conduct spectroscopy at a single-molecule level.
The bonds that keep the distance between atoms in molecules behave like vibrating springs, and these vibrations pulsate at very high frequencies. According to lead author Dr. Rohit Chikkaraddy from the University of Birmingham, these vibrating springs can be excited by mid-infrared region light, which is invisible to the human eye.
At room temperature, the springs are in random motion, so avoiding the thermal noise has been the major challenge in detecting mid-infrared light. Conventional detectors depend on cooled semiconductor tools that are not only bulky but also energy intensive.
The research team presents a new and exciting way to detect this light at room temperature using MIR Vibrationally-Assisted Luminescence (MIRVAL). This technology uses molecules that can be both MIR and visible light.
Dr. Chikkaraddy and his team arranged the molecular emitters into a tiny plasmonic cavity resonant in MIR and visible ranges. These emitters were also further modified to interact with the molecular vibrational and electronic states, leading to efficient transduction of MIR light into improved visible luminescence.
This breakthrough can help scientists deepen their understanding of complex systems and open the possibilities for infrared-active molecular vibrations. The researchers are confident that through further advancements, this novel method can also unlock the potential of manipulating the mechanisms of atoms in molecular quantum systems.
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