Review developments in dual-comb spectroscopy in the mid-infrared and terahertz regions and compare technologies used to generate frequency combs.
Approach:
Technique: Two frequency combs with slightly different pulse rates produce an interference signal that translates optical information into electronically measurable radio frequencies.
Scope: The review covered mid-infrared and terahertz applications, comb-generation technologies, indirect detection methods, and technical barriers.
Key Findings:
Dual-comb spectroscopy can acquire detailed spectra rapidly, with high spectral resolution and precise frequency measurements, without moving components used in some conventional instruments.
The review compared difference-frequency generation, optical parametric oscillators, quantum cascade lasers, electro-optic systems, and microresonators; these approaches differ in range, sensitivity, speed, stability, power, and size.
Mid-infrared applications under development include trace-gas analysis, combustion studies, leak detection, and atmospheric monitoring. Terahertz systems may be used to analyze gases, solids, and biological materials.
Indirect acoustic, thermal, or mechanical detection may help where suitable infrared or terahertz detectors are limited. A cited cavity-enhanced photoacoustic system detected acetylene at 0.6 parts per billion after 100 seconds.
Biomedical applications remain largely at the research stage; the review did not assess a clinically validated diagnostic test.
Interpretation:
The review describes a versatile spectroscopy approach with applications across chemical and materials analysis, while noting that biomedical use is not yet clinically validated.
Limitations:
No single system provides continuous coverage across the full mid-infrared and terahertz range.
Detector noise, cooling requirements, beam alignment, instrument complexity, and maintaining coherence between combs can affect performance.
Conclusion:
Some platforms are becoming smaller and more integrated, but technical barriers remain.
