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1. RF Injection Locking of THz Metasurface Quantum‐Cascade VECSEL

   https://doi.org/10.1002/lpor.202300007  

   Wu, Yu; Curwen, Christopher A.; Shahili, Mohammad; Reno, John L.; Williams, Benjamin S. (August 2023, Laser & Photonics Reviews)

   Abstract Radiofrequency (RF) injection locking and spectral broadening of a terahertz (THz) quantum‐cascade vertical‐external‐cavity surface‐emitting laser (QC‐VECSEL) is demonstrated. An intracryostat VECSEL focusing cavity design is used to enable continuous‐wave lasing with a cavity length over 30 mm, which corresponds to a round‐trip frequency near 5 GHz. Strong RF current modulation is injected to the QC‐metasurface electrical bias to pull and lock the round‐trip frequency. The injection locking range at various RF injection powers is recorded and compared with the injection locking theory. Moreover, the lasing spectrum broadens from 14 GHz in free‐running mode to a maximum spectral width around 110 GHz with 20 dBm of injected RF power. This experimental setup is suitable for further exploration of active mode‐locking and picosecond pulse generation in THz QC‐VECSELs. 

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2. Shaping of Time-Resolved Biphoton Correlations with a Microresonator-Based Spectral Shaper

   https://doi.org/10.1364/CLEO_FS.2024.FTu4F.4  

   Cohen, Lucas M; Wu, Kaiyi; Myilswamy, Karthik V; Lingaraju, Navin B; Lu, Hsuan-Hao; Lukens, Joseph M; Weiner, Andrew M (January 2024, Optica Publishing Group)

   We report on the manipulation of the time-resolved biphoton correlation function using a sub-GHz resolution silicon nitride microresonator-based spectral shaper capa-ble of programmable amplitude and phase modulation. 

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3. 10 GHz Frequency Comb Generation in Lithium Niobate Waveguides with Chirped Poling

   https://doi.org/10.1364/FIO.2023.FTh3E.5  

   Sekhar, Pooja; Wu, Tsung-Han; Ledezma, Luis; Fredrick, Connor; Sekine, Ryoto; Guo, Qiushi; Briggs, Ryan; Marandi, Alireza; Diddams, Scott A (January 2023, Optica Publishing Group)

   We demonstrate efficient 10 GHz frequency comb generation using chirped periodically poled nanophotonic lithium niobate waveguides. Spectral coverage across the UV and visible is achieved with pulse energies less than 50 pJ. 

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4. 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 (December 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 in χ (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. 

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5. 1-GHz mid-infrared frequency comb spanning 3 to 13 μm

   https://doi.org/10.48550/arXiv.2201.07134  

   Hoghooghi, N.; Xing, S.; Chang, P.; Lesko, D.; Lind, A.; Rieker, G.; Diddams, S (July 2022, ArXivorg)

   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 {\mu}m. This frequency comb is based on a commercially available 1.56 {\mu}m mode-locked laser, robust all-fiber Er amplifiers and intra-pulse difference frequency generation (IP-DFG) of few-cycle pulses in \c{hi}(2) nonlinear crystals. When used in a dual comb spectroscopy (DCS) configuration, this source will simultaneously enable measurements with {\mu}s 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. 

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