Browsing by Author "Lou, Minhan"
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Item A compact mid-infrared dual-gas CH4/C2H6 sensor using a single interband cascade laser and custom electronics(SPIE, 2017) Ye, Weilin; Zheng, Chuantao; Tittel, Frank K.; Sanchez, Nancy P.; Gluszek, Aleksander K.; Hudzikowski, Arkadiusz J.; Lou, Minhan; Dong, Lei; Griffin, Robert J.A compact mid-infrared (MIR) dual-gas sensor system was demonstrated for simultaneous detection of methane (CH4) and ethane (C2H6) using a single continuous-wave (CW) interband cascade laser (ICL) based on tunable laser absorption spectroscopy (TDLAS) and wavelength modulation spectroscopy (WMS). Ultracompact custom electronics were developed, including a laser current driver, a temperature controller and a lock-in amplifier. These custom electronics reduce the size and weight of the sensor system as compared with a previous version based on commercial electronics. A multipass gas cell with an effective optical length of 54.6 m was employed to enhance the absorption signal. A 3337 nm ICL was capable of targeting a C2H6 absorption line at 2996.88 cm-1 and a CH4 line at 2999.06 cm-1. Dual-gas detection was realized by scanning both the CH4 and C2H6 absorption lines. Based on an Allan deviation analysis, the 1 σ minimum detection limit (MDL) was 17.4 ppbv for CH4 and 2.4 ppbv for C2H6 with an integration time of 4.3 s. TDLAS based sensor measurements for both indoor and outdoor mixing ratios of CH4 and C2H6 were conducted. The reported single ICL based dual-gas sensor system has the advantages of reduced size and cost without influencing the midinfrared sensor detection sensitivity, selectivity and reliability.Item Compact photoacoustic module for methane detection incorporating interband cascade light emitting device(The Optical Society, 2017) Zheng, Huadan; Lou, Minhan; Dong, Lei; Wu, Hongpeng; Ye, Weilin; Yin, Xukun; Kim, Chul Soo; Kim, Mijin; Bewley, William W.; Merritt, Charles D.; Canedy, Chadwick L.; Warren, Michael V.; Vurgaftman, Igor; Meyer, Jerry R.; Tittel, Frank K.A photoacoustic module (PAM) for methane detection was developed by combining a novel 3.2 μm interband cascade light emitting device (ICLED) with a compact differential photoacoustic cell. The ICLED with a 22-stage interband cascade active core emitted a collimated power of ~700 μW. A concave Al-coat reflector was positioned adjacent to the photoacoustic cell to enhance the gas absorption length. Assembly of the ICLED and reflector with the photoacoustic cell resulted in a robust and portable PAM without any moving parts. The PAM performance was evaluated in terms of operating pressure, sensitivity and linearity. A 1σ detection limit of 3.6 ppmv was achieved with a 1-s integration time.Item CW DFB-QCL and EC-QCL based sensor for simultaneous NO and NO2 measurements via frequency modulation multiplexing using multi-pass absorption spectroscopy(SPIE, 2017) Yu, Yajun; Sanchez, Nancy P.; Lou, Minhan; Zheng, Chuantao; Wu, Hongpeng; Głuszek, Aleksander K.; Hudzikowski, Arkadiusz J.; Griffin, Robert J.; Tittel, Frank K.Nitrogen oxides (NOx), including nitric oxide (NO) and nitrogen dioxide (NO2) play important roles in determining the photochemistry of the ambient atmosphere, controlling the production of tropospheric ozone, affecting the concentration levels of the hydroxyl radical, and forming acid precipitation. A sensor system capable of simultaneous measurements of NO and NO2 by using a commercial 76 m astigmatic multi-pass gas cell (MPGC) was developed in order to enable fast-response NOx detection. A continuous wave (CW), distributed-feedback (DFB) quantum cascade laser (QCL) and a CW external-cavity (EC) QCL were employed for targeting a NO absorption doublet at 1900.075 cm-1 and a NO2 absorption line at 1630.33 cm-1, respectively. Both laser beams were combined and transmitted through the MPGC in an identical optical path and subsequently detected by a single mid-infrared detector. A frequency modulation multiplexing scheme was implemented by modulating the DFB-QCL and EC-QCL at different frequencies and demodulating the detector signal with two Labview software based lock-in amplifiers to extract the corresponding second-harmonic (2f) components. Continuous monitoring of NO and NO2 concentration levels was achieved by locking the laser frequencies to the selected absorption lines utilizing a reference cell filled with high concentrations of NO and NO2. The experimental results indicate minor performance degradation associated with frequency modulation multiplexing and no cross talk between the two multiplexed detection channels. The performance of the reported sensor system was evaluated for real time, sensitive and precise detection of NO and NO2 simultaneously.Item Dual-feedback mid-infrared cavity-enhanced absorption spectroscopy for H2CO detection using a radio-frequency electrically-modulated interband cascade laser(The Optical Society, 2018) He, Qixin; Zheng, Chuantao; Lou, Minhan; Ye, Weilin; Wang, Yiding; Tittel, Frank K.A mid-infrared cavity-enhanced sensor system was demonstrated for the detection of formaldehyde (H2CO) using a continuous-wave (cw) interband cascade laser (ICL) centered at 3599 nm. A compact Fabry-Perot (F-P) cavity with a physical size of 38 × 52 × 76 mm3 was developed consisting of two concave mirrors with a radius of curvature of 80 mm and a reflectivity of 99.8% at 3.6 μm. Different from the widely reported electro-optical (EO) external modulation based Pound-Drever-Hall (PDH) locking technique, a radio-frequency electrical internal modulation based PDH technique was used for locking the laser mode to the cavity mode. A dual-feedback control on the laser current and on the piezo transducer (PZT) displacement was utilized for further stabilizing mode locking. A 20 m effective optical path length was achieved with a cavity length of 2 cm and a finesse of 1572. The effectiveness and sensitivity of the sensor system were demonstrated by targeting an absorption line at 2778.5 cm−1 for H2CO measurements. A linear relation between the cavity transmitted signal amplitude and the H2CO concentration was obtained within the range of 0−5 ppm. A 1σ detection limit of 25 parts-per-billion (ppb) was achieved with an averaging time of 1 s based on Allan-Werle variance analysis. The reported dual-feedback RF modulation based PDH technique led to a method for gas detection using a similar experimental setup and measurement scheme.Item Engineering chirality at wafer scale with ordered carbon nanotube architectures(Springer Nature, 2023) Doumani, Jacques; Lou, Minhan; Dewey, Oliver; Hong, Nina; Fan, Jichao; Baydin, Andrey; Zahn, Keshav; Yomogida, Yohei; Yanagi, Kazuhiro; Pasquali, Matteo; Saito, Riichiro; Kono, Junichiro; Gao, Weilu; Carbon Hub; Smalley-Curl InstituteCreating artificial matter with controllable chirality in a simple and scalable manner brings new opportunities to diverse areas. Here we show two such methods based on controlled vacuum filtration - twist stacking and mechanical rotation - for fabricating wafer-scale chiral architectures of ordered carbon nanotubes (CNTs) with tunable and large circular dichroism (CD). By controlling the stacking angle and handedness in the twist-stacking approach, we maximize the CD response and achieve a high deep-ultraviolet ellipticity of 40 ± 1 mdeg nm−1. Our theoretical simulations using the transfer matrix method reproduce the experimentally observed CD spectra and further predict that an optimized film of twist-stacked CNTs can exhibit an ellipticity as high as 150 mdeg nm−1, corresponding to a g factor of 0.22. Furthermore, the mechanical rotation method not only accelerates the fabrication of twisted structures but also produces both chiralities simultaneously in a single sample, in a single run, and in a controllable manner. The created wafer-scale objects represent an alternative type of synthetic chiral matter consisting of ordered quantum wires whose macroscopic properties are governed by nanoscopic electronic signatures and can be used to explore chiral phenomena and develop chiral photonic and optoelectronic devices.Item Repetitively Mode-Locked Cavity-Enhanced Absorption Spectroscopy (RML-CEAS) for Near-Infrared Gas Sensing(MDPI, 2017) He, Qixin; Lou, Minhan; Zheng, Chuantao; Ye, Weilin; Wang, Yiding; Tittel, Frank K.A Pound-Drever-Hall (PDH)-based mode-locked cavity-enhanced sensor system was developed using a distributed feedback diode laser centered at 1.53 µm as the laser source. Laser temperature scanning, bias control of the piezoelectric ceramic transducer (PZT) and proportional-integral-derivative (PID) feedback control of diode laser current were used to repetitively lock the laser modes to the cavity modes. A gas absorption spectrum was obtained by using a series of absorption data from the discrete mode-locked points. The 15 cm-long Fabry-Perot cavity was sealed using an enclosure with an inlet and outlet for gas pumping and a PZT for cavity length tuning. The performance of the sensor system was evaluated by conducting water vapor measurements. A linear relationship was observed between the measured absorption signal amplitude and the H2O concentration. A minimum detectable absorption coefficient of 1.5 × 10–8 cm–1 was achieved with an averaging time of 700 s. This technique can also be used for the detection of other trace gas species by targeting the corresponding gas absorption line.Item Theoretical Studies of Optical Properties and Photocatalytic Applications of Aluminum Nanoparticles with Sharp Corners(2021-01-05) Lou, Minhan; Nordlander, PeterAluminum is emerging as an alternative plasmonic material to traditional novel material like Au and has shown great potentials in plasmonic photocatalysis. Here I have performed comprehensive theoretical investigations on Al nanoparticles with various shapes which have been chemically synthesized by collaborators. We find that nanoparticles with sharp corners such as Al nanocubes and Al octopods possess much larger localized electric field enhancement around the corners than traditional spherical-like nanocrystals. As result, substantially increased near-field coupling of Al nanocube with metal substrate can provide more tunability of plasmonic resonant wavelength and further field enhancements. We demonstrate theoretically and experimentally that Al nanocubes can significantly improve the photocatalytic reactivity of poor plasmonic Pd deposited on nanocube corners. Pristine Al nanocrystals also show morphology-dependent photocatalytic reactivity in H2 dissociation experiments. I develop new Al hot-carriers (HC) generation model to explain the experimental results. The theory shows HC generation rates of Al octopods is 5 times higher than Al spherical-like nanocrystal and 2 times higher than Al nanocubes.Item Vacuum Bloch–Siegert shift in Landau polaritons with ultra-high cooperativity(Springer Nature, 2018) Li, Xinwei; Bamba, Motoaki; Zhang, Qi; Fallahi, Saeed; Gardner, Geoff C.; Gao, Weilu; Lou, Minhan; Yoshioka, Katsumasa; Manfra, Michael J.; Kono, JunichiroA two-level system resonantly interacting with an a.c. magnetic or electric field constitutes the physical basis of diverse phenomena and technologies. However, Schrödinger’s equation for this seemingly simple system can be solved exactly only under the rotating-wave approximation, which neglects the counter-rotating field component. When the a.c. field is sufficiently strong, this approximation fails, leading to a resonance-frequency shift known as the Bloch–Siegert shift. Here, we report the vacuum Bloch–Siegert shift, which is induced by the ultra-strong coupling of matter with the counter-rotating component of the vacuum fluctuation field in a cavity. Specifically, an ultra-high-mobility two-dimensional electron gas inside a high-Qterahertz cavity in a quantizing magnetic field revealed ultra-narrow Landau polaritons, which exhibited a vacuum Bloch–Siegert shift up to 40 GHz. This shift, clearly distinguishable from the photon-field self-interaction effect, represents a unique manifestation of a strong-field phenomenon without a strong field.