Imaging absorption spectroscopy with laser frequency combs simultaneously measures 64 spectra at 250-MHz resolution over a span of 4 nm, within 3 seconds. At 1000 s averaging, the high signal-to-noise ratio reaches 250 per pixel.
Time-resolved near-infrared absorption spectroscopy of single non-repeatable transient events is performed at high spectral resolution with a dual-comb interferometer using a continuous-wave laser followed by a single electro-optic amplitude modulator. By sharing high-speed electrical/optical components, our spectrometer greatly simplifies the implementation of dual-comb spectroscopy and offers a high mutual coherence time, measured up to 50 s, without any active stabilization system and/or data processing. The time resolution is as short as 100 µs in our experimental demonstration. For a span of 36 GHz, the mean signal-to-noise ratio of 80, at 100-MHz spectral resolution and 100-µs measurement time, enables precise determination of the parameters of rovibrational lines, including intensity or concentration.
A study regarding the performance comparison of three different types of long-distance fiber Bragg grating (FBG) sensors based on bidirectional Raman and erbium-doped fiber (EDF) amplification has been carried out to determine the most power-efficient and accurate configuration. The three sensor system configurations studied were a bidirectional hybrid Raman amplifier with (Type I) an EDF located after the distributed Raman amplification section, (Type II) an EDF located before the distributed Raman amplification section, and (Type III) without an EDF. The FBG sensor systems are based on a demodulation scheme employing radio frequency power measurements of a beat signal, in which a sine-modulated amplified spontaneous emission from a directly modulated reflective semiconductor optical amplifier is employed as a broadband light source. The results of our experimentation showed that the sensor system with the EDF located prior to the Raman amplification section provided the best performance in regards to its pump power efficiency, electrical signal-to-noise ratio, and measurement accuracy.
We demonstrate dual-comb interferometry and spectroscopy with a III-V-on-silicon passively mode-locked laser of 1-GHz repetition rate and 1-THz span. We heterodyne the on-chip device with an electro-optic modulator comb for initial assessment.
A single electro-optic modulator enables near-infrared dual-comb spectroscopy over a span of 40 GHz with a 150-kHz refresh rate and a 50-s coherence time. The signal-to-noise ratio is 950 at 100-MHz resolution and 100-ms measurement.
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