Capturing an Elusive Light Spectrum

A research team led by EPFL recently registered success for building ultra-high quality optical cavities for elusive mid-infrared spectral regions. This will open up doors for new biological sensors, chemical sensors, and several better technologies. The spectral window of mid-infrared waves, also called the “molecular fingerprint region” included the light wavelengths in range of 2.5 – 20 μm. This new success is a critical one for the field of spectroscopy, biological sensing, materials science, and rest of the industry. The range defined here is the one that can be utilized for detection of numerous organic molecules. It also includes two different ranges that permit signal transmission through our surroundings without any loss or distortion.

Capturing elusive spectrum

One of the most powerful ways for capturing the potential of mid-infrared spectral window is through optical cavities, micro-devices that are capable of restricting light for quite an extended period of time. But devices like these are yet to be explored as there are multiple challenges in the way. The research team that was led by EPFL accepted the challenge and successfully showcased how crystalline substances can be used in creation of perfect quality optical cavities that harbor mid-infrared spectral region symbolizing the epitome of values that can be gained by any mid-infrared resonator till now.

In order to build the ultra-high quality microcavities, the team used crystals of alkaline earth metal fluoride that were manually polished. The team also developed uncovered chalcogenide tapered fibers to cover mid-infrared light from consistent wave Quantum Cascade Laser (QCL) in their crystalline microcavities. And lastly, the cavity ring-down spectroscopy techniques allowed the team to showcase ultra-high quality resonators at depth in the mid-infrared spectral range unambiguously. The team also showed that the microcavity quality is restricted by multi-photon absorption. It is one phenomenon where the quasiparticles, the phonons that are formed from vibration and energy in cavity crystal disrupt and interact with light simultaneously.