Surface‐Enhanced Dual‐Comb Coherent Raman Spectroscopy with Nanoporous Gold Films

Abstract

With two asynchronous frequency combs beating on a single detector, dual‐comb spectroscopy (DCS) enables rapid, broadband, and precise molecular fingerprinting on a comb tooth‐by‐tooth basis and thus holds much promise in molecular sensing. Sensitivity, however, has been an Achilles’ heel of this technique. Here, an approach for ultrasensitive nonlinear DCS based on plasmon‐enhanced coherent Raman spectroscopy (CRS) with ultrathin (100 nm) nanoporous gold films is presented. A high‐resolution (<8 cm−1) Raman spectrum is obtained within 32.8 µs for characterizing low‐density chemicals. The achieved sensitivity enhancement reaches ≈106–8 relative to nonenhanced dual‐comb CRS of liquid samples. The demonstrated approach may open up a new avenue for fast identification of trace amounts of chemicals.

High-resolution imaging of graphene by tip-enhanced coherent anti-Stokes Raman scattering

“…5(f)), and after deducting the background, the CARS signal intensity is 10 Counts. The EF TECARS=CARS is about 3 Â 10 4 , close to SECARS EF, 36,37 calculated by the equation EF ¼ I nf =N nf I ff =N ff , where I nf and I ff are the neareld and far-¯eld intensities and N nf and N ff are the corresponding numbers of molecules contributing to each signal. 46…”

“…In this paper, graphene sample was imaged by TECARS, and this is the¯rst TECARS report imaging single atom layer at one of the highest resolutions of 20 nm by Au tip. The highest EF TECARS=CARS is about 10 4 , which is even close to SECARS 36,37 and had never been seen in TECARS experiments before. With technological improvement, it is expected that there is a bright future for biological, chemical and medical application of TECARS.…”

“…Before this, single molecular detection by TECARS has only been theoretically demonstrated. Sensitivity, EF and resolution are the major challenges of TECARS technique and our data show the highest EF TECARS=CARS is about $10 4 , which has never been measured in TECARS reports and have the similar order of magnitude with SECARS 36,37 (EF of tip is usually smaller than that of substrates). The highest resolution is about 20 nm, the same as the highest TECARS resolution which have ever been reported.…”

“…Here, we experimentally found the highest EF TECARS=CARS can reach 10 4 which is even almost near the EF of SECARS. 36,37 Figure 5 shows the TECARS imaging of graphene with tip approaching the sample (Figs. 5(a TECARS signal intensity of graphene and background signal near the tip apex are about 3:8 Â 10 5 and 9:6 Â 10 4 Counts, respectively ( Fig.…”

Raman Excitation of Hydrogen Molecules to v = 1 State

“…CARS is a very effective non-linear spectroscopic technique that has been used in various applications such as temperature and concentration measurements, molecular relaxation processes, gas-phase and plasma diagnostics and femtosecond chemistry (El-Diasty, 2011;Lempert & Adamovich, 2014;Tolles et al, 1977;Zheltikov, 2000). CARS spectroscopy has been a common means of detection for modern optical experiments and comprehensively mentioned in literature (Christensen et al, 2019;Eckbreth, 1996;Eesley, 2013;Harvey & Nibler, 1978;Jiang et al, 2020;Kifer, 1980;Short et al, 2015;Yan et al, 2018;Yang et al, 2018).…”