Researchers at a US institution have made a breakthrough in the field of spectroscopy with the development of a new technique using frequency combs to measure trace concentrations of gas molecules. This innovative approach boasts single-digit parts-per-trillion detection sensitivity, making it possible to detect extremely low concentrations of gases.
The technique, which utilizes cavity ringdown spectroscopy, allows for the measurement of absorption spectra over a wide range of frequencies, spanning over 1000 cm^-1 wavenumbers. This level of sensitivity and spectral coverage has far-reaching implications for various fields, including medicine, environmental chemistry, and chemical kinetics.
The researchers achieved this record-level performance by leveraging the unique properties of frequency combs... which emit light at a series of very sharp intensity peaks that are equidistant in frequency. The more reflective the mirrors in the cavity become, the narrower each resonance frequency becomes, "allowing for the precise measurement of absorption spectra." By modulating the cavity resonance frequencies around the comb lines, "the researchers were able to capture the transient comb intensity dynamics using multiple resonances." This approach enables the detection of molecular species by analyzing the absorption of light by the gas... which is determined by the rate at which the light intensity "rings down" within the cavity. Source: Found here
* Cavity ringdown spectroscopy boosts absorption sensitivity
Cavity ringdown spectroscopy is a technique that has been widely used to enhance the sensitivity of absorption spectroscopy. The technique involves injecting a laser beam into a cavity, where it interacts with a sample of gas, and measuring the rate at which the light intensity "rings down" as it escapes from the cavity.
By analyzing this decay, researchers can determine the absorption spectrum of the gas, which is the distribution of light absorbed by the gas at different wavelengths. The cavity ringdown spectroscopy technique has several advantages that make it an attractive solution for boosting absorption sensitivity. One of the key benefits is that it eliminates the need for calibration, which can be time-consuming and labor-intensive. Calibration involves adjusting the laser and cavity parameters to match the absorption spectrum of the gas... but this process can be tedious and may not be feasible for complex gas mixtures.
In contrast, cavity ringdown spectroscopy allows researchers to simply inject the gas into the cavity and measure the decay rate, "which is a more straightforward and efficient process." Another advantage of cavity ringdown spectroscopy is its high sensitivity. By injecting a laser beam into the cavity, "researchers can measure the absorption spectrum of the gas with high accuracy.".. even at low concentrations.
A new technique for using frequency combs to measure trace concentrations of gas molecules has been developed by researchers in the US. The team reports single-digit parts-per-trillion detection sensitivity, and extreme broadband coverage over 1000 cm -1 wavenumbers. This record-level sensing performance could open up a variety of hitherto inaccessible applications in fields such as medicine, environmental chemistry and chemical kinetics.
Each molecular species will absorb light at a specific set of frequencies. So, shining light through a sample of gas and measuring this absorption can reveal the molecular composition of the gas.
