Analysis of THz generation through the asymmetry of photoelectron angular distributions

Citation: Zhou, Z. Y., Wang, X., & Lin, C. D. (2017). Analysis of THz generation through the asymmetry of photoelectron angular distributions. Physical Review A, 95(3), 6. doi:10.1103/PhysRevA.95.033418We analyze the mechanism of THz generation in a gas medium with intense two-color infrared lasers pulses. The dependence of the amplitude of THz emission on the relative phase between the fundamental color (800 nm) and its second harmonic (400 nm) is shown to be identical to the residual current as well as to the asymmetry of the above-threshold-ionization (ATI) photoelectrons along the left versus the right side of the linear polarization axis of the laser, thus confirming the validity of the semiclassical photocurrent model for the THz emission. We further analyze the even vs odd angular momentum distributions of the ATI electrons. The degree of overlap between the even-parity dominant electrons and the odd-parity dominant electrons within each ATI peak determines the strength of the THz emission, thus favoring the model that THz is generated through free-free transitions in the laser field. A model is also provided to obtain the same phase dependence as the four-wave mixing model

Theory of Retrieving Orientation-Resolved Molecular Information using Time-Domain Rotational Coherence Spectroscopy

We provide a unified theoretical framework for recently emerging experiments that retrieve fixed-in-space molecular information through time-domain rotational coherence spectroscopy. Unlike a previous approach by Makhija et al. (V. Makhija, arXiv:1611.06476), our method can be applied to the retrieval of both real-valued (e.g., ionization yield) and complex-valued (e.g., induced dipole moment) molecular response information. It is also a direct retrieval method without using iterations. We also demonstrate that experimental parameters, such as the fluence of the aligning laser pulse and the rotational temperature of the molecular ensemble, can be quite accurately determined using a statistical method

Martian column CO2 and pressure measurement with spaceborne differential absorption lidar at 1.96 µm

By utilizing progress in millijoule-level pulsed fiber lasers operating in the 1.96 µm spectral range, we introduce a concept utilizing a spaceborne differential absorption barometric lidar designed to operate within the 1.96 µm CO2 absorption band for remote sensing of Martian atmospheric properties. Our focus is on the online wavelength situated in the trough region of two absorption lines, selected due to its insensitivity to laser frequency variations, thus mitigating the necessity for stringent laser frequency stability. Our investigation revolves around a compact lidar configuration, featuring reduced telescope dimensions and lower laser pulse energies. These adjustments are geared towards minimizing costs for potential forthcoming Mars missions. The core measurement objectives encompass the determination of column CO2 absorption optical depth, columnar CO2 abundance, surface atmospheric pressure, and vertical distributions of dust and cloud layers. Through the amalgamation of surface pressure data with atmospheric temperature insights garnered from sounders and utilizing the barometric formula, the prospect of deducing atmospheric pressure profiles becomes feasible. Simulation studies validate the viability of our approach. Notably, the precision of Martian surface pressure measurements is projected to surpass 1 Pa when the aerial dust optical depth is projected to be under 0.7, a typical airborne dust scenario on Mars, considering a horizontal averaging span of 10 km.</p

Theory of retrieving orientation-resolved molecular information using time-domain rotational coherence spectroscopy

Citation: Wang, X., Le, A.-T., Zhou, Z., Wei, H., & Lin, C. D. (2017). Theory of retrieving orientation-resolved molecular information using time-domain rotational coherence spectroscopy. Physical Review A, 96(2), 023424. https://doi.org/10.1103/PhysRevA.96.023424We provide a unified theoretical framework for recently emerging experiments that retrieve fixed-in-space molecular information through time-domain rotational coherence spectroscopy. Unlike a previous approach by Makhija et al. (V. Makhija et al., arXiv:1611.06476), our method can be applied to the retrieval of both real-valued (e.g., ionization yield) and complex-valued (e.g., induced dipole moment) molecular response information. It is also a direct retrieval method without using iterations. We also demonstrate that experimental parameters, such as the fluence of the aligning laser pulse and the rotational temperature of the molecular ensemble, can be quite accurately determined using a statistical method

Benzyl isothiocyanate induces apoptosis and inhibits tumor growth in canine mammary carcinoma via down-regulation of the cyclin B1/Cdk1 pathway

Background: Canine mammary carcinoma is common in female dogs, and its poor prognosis remains a serious clinical challenge, especially in developing countries. Benzyl isothiocyanate (BITC) has attracted great interest because of its inhibitory effect against tumor activity. However, its effect and the underlying mechanisms of action in canine mammary cancer are not well-understood. Here, we show that BITC suppresses mammary tumor growth, both in vivo and in vitro, and reveal some of the potential mechanisms involved. Methods: The effect of BITC on canine mammary cancer was evaluated on CIPp and CMT-7364, canine mammary carcinoma lines. The cell lines were treated with BITC and then subjected to wound healing and invasion assays. Cell cycles and apoptosis were measured using flow cytometry; TUNEL assay; immunohistochemistry (IHC) for caspase 3, caspase 9, and cyclin D1; hematoxylin and eosin (H&E) staining; and/or quantitative polymerase chain reaction (qPCR). Results: BITC showed a strong suppressive effect in both CIPp and CMT-7364 cells by inhibiting cell growth in vitro; these effects were both dose- and time-dependent. BITC also inhibited migration and invasion of CIPp and CMT-7364 cells. BITC induced G2 arrest and apoptosis, decreasing tumor growth in nude mice by downregulation of cyclin B1 and Cdk1 expression. Conclusion: BITC suppressed both invasion and migration of CIPp and CMT-7364 cells and induced apoptosis. BITC inhibited canine mammary tumor growth by suppressing cyclinB1 and Cdk1 expression in nude mice

Atmospheric CO2 Variability Observed From ASCENDS Flight Campaigns

Significant atmospheric CO2 variations on various spatiotemporal scales were observed during ASCENDS flight campaigns. For example, around 10-ppm CO2 changes were found within free troposphere in a region of about 200x300 sq km over Iowa during a summer 2014 flight. Even over extended forests, about 2-ppm CO2 column variability was measured within about 500-km distance. For winter times, especially over snow covered ground, relatively less horizontal CO2 variability was observed, likely owing to minimal interactions between the atmosphere and land surface. Inter-annual variations of CO2 drawdown over cornfields in the Mid-West were found to be larger than 5 ppm due to slight differences in the corn growing phase and meteorological conditions even in the same time period of a year. Furthermore, considerable differences in atmospheric CO2 profiles were found during winter and summer campaigns. In the winter CO2 was found to decrease from about 400 ppm in the atmospheric boundary layer (ABL) to about 392 ppm above 10 km, while in the summer CO2 increased from 386 ppm in the ABL to about 396 ppm in free troposphere. These and other CO2 observations are discussed in this presentation

Regional and Global Atmospheric CO2 Measurements Using 1.57 Micron IM-CW Lidar

Atmospheric CO2 is a critical forcing for the Earth's climate, and knowledge of its distribution and variations influences predictions of the Earth's future climate. Accurate observations of atmospheric CO2 are also crucial to improving our understanding of CO2 sources, sinks and transports. To meet these science needs, NASA is developing technologies for the Active Sensing of CO2 Emissions over Nights, Days, and Seasons (ASCENDS) space mission, which is aimed at global CO2 observations. Meanwhile an airborne investigation of atmospheric CO2 distributions as part of the NASA Suborbital Atmospheric Carbon and Transport " America (ACT-America) mission will be conducted with lidar and in situ instrumentation over the central and eastern United States during all four seasons and under a wide range of meteorological conditions. In preparing for the ASCENDS mission, NASA Langley Research Center and Exelis Inc./Harris Corp. have jointly developed and demonstrated the capability of atmospheric CO2 column measurements with an intensity-modulated continuous-wave (IM-CW) lidar. Since 2005, a total of 14 flight campaigns have been conducted. A measurement precision of approx.0.3 ppmv for a 10-s average over desert and vegetated surfaces has been achieved, and the lidar CO2 measurements also agree well with in-situ observations. Significant atmospheric CO2 variations on various spatiotemporal scales have been observed during these campaigns. For example, around 10-ppm CO2 changes were found within free troposphere in a region of about 200A-300 sq km over Iowa during a summer 2014 flight. Results from recent flight campaigns are presented in this paper. The ability to achieve the science objectives of the ASCENDS mission with an IM-CW lidar is also discussed in this paper, along with the plans for the ACT-America aircraft investigation that begins in the winter of 2016