More Like this

1. Broadband 1-GHz mid-infrared frequency comb

   https://doi.org/10.1038/s41377-022-00947-w  

   Hoghooghi, Nazanin; Xing, Sida; Chang, Peter; Lesko, Daniel; Lind, Alexander; Rieker, Greg; Diddams, Scott (September 2022, Light: Science & Applications)

   Abstract Mid-infrared (MIR) spectrometers are invaluable tools for molecular fingerprinting and hyper-spectral imaging. Among the available spectroscopic approaches, GHz MIR dual-comb absorption spectrometers have the potential to simultaneously combine the high-speed, high spectral resolution, and broad optical bandwidth needed to accurately study complex, transient events in chemistry, combustion, and microscopy. However, such a spectrometer has not yet been demonstrated due to the lack of GHz MIR frequency combs with broad and full spectral coverage. Here, we introduce the first broadband MIR frequency comb laser platform at 1 GHz repetition rate that achieves spectral coverage from 3 to 13 µm. This frequency comb is based on a commercially available 1.56 µm mode-locked laser, robust all-fiber Er amplifiers and intra-pulse difference frequency generation (IP-DFG) of few-cycle pulses inχ⁽²⁾nonlinear crystals. When used in a dual comb spectroscopy (DCS) configuration, this source will simultaneously enable measurements with μs time resolution, 1 GHz (0.03 cm⁻¹) spectral point spacing and a full bandwidth of >5 THz (>166 cm⁻¹) anywhere within the MIR atmospheric windows. This represents a unique spectroscopic resource for characterizing fast and non-repetitive events that are currently inaccessible with other sources. 

   more » « less
2. High power, room temperature, terahertz sources and frequency comb based on difference-frequency generation at CQD

   https://doi.org/10.1117/12.2635322  

   Razeghi, Manijeh (September 2022, Terahertz Emitters, Receivers, and Applications XIII)

   Razeghi, Manijeh; Baranov, Alexei N. (Ed.)

   Quantum cascade laser (QCL) is becoming the leading laser source in the mid-infrared and terahertz range due to its rapid development in power, efficiency, and spectral covering range. Owing to its unique intersubband transition and fast carrier lifetime, QCL possesses strong nonlinear susceptibilities that makes it the ideal platform for a variety of nonlinear optical generations. Among this, terahertz (THz) source based on difference-frequency generation (DFG) and frequency comb based on four wave mixing effect are the most exciting phenomena which could potentially revolutionize spectroscopy in mid-infrared (mid-IR) and THz spectral range. In this paper, we will briefly discuss the recent progress of our research. This includes high power high efficiency QCLs, high power room temperature THz sources based on DFG-QCL, room temperature THz frequency comb, and injection locking of high-power QCL frequency combs. The developed QCLs are great candidates as next generation mid-infrared source for spectroscopy and sensing. 

   more » « less
3. Mid-infrared cross-comb spectroscopy

   https://doi.org/10.1038/s41467-023-36811-7  

   Liu, Mingchen; Gray, Robert M.; Costa, Luis; Markus, Charles R.; Roy, Arkadev; Marandi, Alireza (February 2023, Nature Communications)

   Abstract Dual-comb spectroscopy has been proven beneficial in molecular characterization but remains challenging in the mid-infrared region due to difficulties in sources and efficient photodetection. Here we introduce cross-comb spectroscopy, in which a mid-infrared comb is upconverted via sum-frequency generation with a near-infrared comb of a shifted repetition rate and then interfered with a spectral extension of the near-infrared comb. We measure CO₂absorption around 4.25 µm with a 1-µm photodetector, exhibiting a 233-cm⁻¹instantaneous bandwidth, 28000 comb lines, a single-shot signal-to-noise ratio of 167 and a figure of merit of 2.4 × 10⁶Hz^1/2. We show that cross-comb spectroscopy can have superior signal-to-noise ratio, sensitivity, dynamic range, and detection efficiency compared to other dual-comb-based methods and mitigate the limits of the excitation background and detector saturation. This approach offers an adaptable and powerful spectroscopic method outside the well-developed near-IR region and opens new avenues to high-performance frequency-comb-based sensing with wavelength flexibility. 

   more » « less
4. Broadband photothermal spectroscopy with a mid-infrared quantum cascade laser frequency comb

   https://doi.org/10.1364/OE.544229  

   Huang, Baichuan; Gomółka, Grzegorz; Mikkonen, Tommi; Wysocki, Gerard (January 2025, Optics Express)

   We demonstrate a broadband photothermal spectroscopy in the mid-infrared region using a quantum cascade laser frequency comb operating between ∼7.7 and ∼8.2 µm covering a frequency range of ∼70 cm^-1. The photothermal spectroscopy technique employs a Mach-Zehnder interferometer operating in a pump-probe configuration, where the mid-infrared pump beam is modulated by a Fourier transform spectrometer. A 76-m Herriott-type multipass cell is used for signal enhancement. As a proof-of-concept, we have measured the photothermal spectra of nitrous oxide that show good agreement with the HITRAN database. A minimum detection limit of 83 ppb of nitrous oxide in nitrogen is estimated from a broadband photothermal spectrum with 9.9 GHz spectral point spacing and acquired over 78 minutes. This detection scheme also provides over three orders of magnitude of photothermal signal linearity with gas concentration. This spectroscopic method combines the functionality of high sensitivity and background-free detection of photothermal spectroscopy as well as broadband mid-infrared operation of quantum cascade laser frequency comb, which could find applications in trace gas sensing systems that benefit from these features. 

   more » « less
5. Thermal-light heterodyne spectroscopy with frequency comb calibration

   https://doi.org/10.1364/OPTICA.440389  

   Fredrick, Connor; Olsen, Freja; Terrien, Ryan; Mahadevan, Suvrath; Quinlan, Franklyn; Diddams, Scott_A (February 2022, Optica)

   Precision laser spectroscopy is key to many developments in atomic and molecular physics and the advancement of related technologies such as atomic clocks and sensors. However, in important spectroscopic scenarios, such as astronomy and remote sensing, the light is of thermal origin, and interferometric or diffractive spectrometers typically replace laser spectroscopy. In this work, we employ laser-based heterodyne radiometry to measure incoherent light sources in the near-infrared and introduce techniques for absolute frequency calibration with a laser frequency comb. Measuring the solar continuum, we obtain a signal-to-noise ratio that matches the fundamental quantum-limited prediction given by the thermal photon distribution and our system’s efficiency, bandwidth, and averaging time. With resolving power $R\sim <\#comment/>{10}^6$, we determine the center frequency of an iron line in the solar spectrum to sub-MHz absolute frequency uncertainty in under 10 min, a fractional precision 1/4000 the linewidth. Additionally, we propose concepts that take advantage of refractive beam shaping to decrease the effects of pointing instabilities by $100\times <\#comment/>$, and of frequency comb multiplexing to increase data acquisition rates and spectral bandwidths by comparable factors. Taken together, our work brings the power of telecommunications photonics and the precision of frequency comb metrology to laser heterodyne radiometry, with implications for solar and astronomical spectroscopy, remote sensing, and precise Doppler velocimetry. 

   more » « less