Optical single-sideband modulation for a coherent Doppler lidar.

The performance of bulk InSb mixers is investigated, A heterodyne experiment has been performed at 69 GHz with IF's varying from 0.4 to 20 MHz. In this experiment the conversion loss was measured as a function of the intermediate frequency (IF) for ambient temperatures in the range 1.5 to 20°K. The IF at which the conversion loss increased by 3 dB determined the response time. Using an electron temperature model, expressions for the conversion loss and the response time are derived by making a small-signal expansion of an energy balance equation. Good agreement between theory and experiment is shown. In this theory the InSb mixer is viewed as a bolometer mixer. An evaluation of mixer performance, stressing operation at ambient temperatures in the 1.5 to 20°K range, is presented. The available tradeoffs between conversion loss and response time as a function of ambient temperature and applied fields are given. Values as low as 11 dB for the minimum conversion loss can be obtained at 1.5°K, where the maximum useable IF is 1 MHz. To obtain a substantially higher IF, such as 10 MHz, the temperature must be increased to 16°K. However, the optimum conversion loss increases at a rate of 1 dB/°K and is 27 dB at 16°K. It is also shown that the device performance of InSb mixers can be predicted satisfactorily from static I-V characteristics and that the best mixer material can be determined by making simple dc measurements.

Recent advances in fiber optic component technology and digital processing components have enabled the development of a new coherent doppler lidar (CDL) system based upon a fiber optic FMCW, which has small size and light weight. CDL can give high precision velocity measurements data and range measurements data which support space craft safe landing. We designed and implemented a CDL of all-fiber structure in this article. First of all, FMCW ranging theory was described. Second, the CDL architecture of the system was discussed. Last, we introduced radar fiber Coupling and signal processor part, which include signal acquisition hardware, signal processing of dedicated FFT based on FPGA. The experimental program and experimental results were presented in the paper. We analyzed the experimental results carefully. From the results, the project has the advantage of large velocimetry range (−100m/S∼+100m/S) and high velocimetry accuracy (0.5%). It completely meted the requirement of Space Craft Safe Landing.

An all‐fiber pulsed coherent Doppler LIDAR (CDL) system is described. It uses a fiber laser as a light source at a 1.54‐μm wavelength, producing 200 μJ pulses at 10 kHz. The local oscillator signal is mixed with the backscattered light (of different frequency) in the fiber. The atmospheric wind speed is determined through the fast Fourier transform applied to the difference frequency signal acquired by an analog‐to‐digital converter card. This system was used to measure the atmospheric wind above the upper‐air meteorological observatory in Rongcheng (37.10°N, 122.25°E) of China between January 7 and 19, 2015. The CDL data are compared with sounding‐ and pilot‐balloon measurements to assess the CDL performance. The results show that the correlation coefficient of the different wind‐speed measurements is 0.93 and their discrepancy 0.64 m/s; the correlation coefficient for wind‐direction values is 0.92 and their discrepancy 5.8 deg. A time serial of the wind field, which benefits the understanding of atmospheric dynamics, is presented after the comparisons between data from CDL and balloons. The CDL system has a compact structure and demonstrates good stability, reliability, and a potential for application to wind‐field measurements in the atmospheric boundary layer.

The direct and indirect radiation forcing of aerosol particles deeply affect the energy budget and the atmospheric chemical and physical processes. To retrieve the vertical aerosol mass fluxes and to investigate the vertical transport process of aerosol by a coherent Doppler lidar (CDL), a practical method for instrumental calibration and aerosol optical properties retrieval based on CDL and sun photometer synchronization observations has been developed. A conversion of aerosol optical properties to aerosol microphysical properties is achieved by applying a well-developed algorithm. Furthermore, combining the vertical velocity measured simultaneously with a CDL, we use the eddy covariance (EC) method to retrieve the vertical turbulent aerosol mass fluxes by a CDL and sun photometer with a spatial resolution of 15 m and a temporal resolution of 1 s throughout the planetary boundary layer (PBL). In this paper, we present a measurement case of 24-h continuous fluxes observations and analyze the diurnal variation of the vertical velocity, the aerosol backscatter coefficient at 1550 nm, the mean aerosol mass concentration, and the vertical aerosol mass fluxes on 13 April 2020. Finally, the main relative errors in aerosol mass flux retrieval, including sample error σF,S, aerosol optical properties retrieval error σF,R, and error introduced from aerosol microphysical properties retrieval algorithm σF,I, are evaluated. The sample error σF,S is the dominating error which increases with height except during 12:00–13:12 LST. The aerosol optical properties retrieval error σF,R is 21% and the error introduced from the aerosol microphysical properties retrieval algorithm σF,I is less than 50%.

The performance of a coherent Doppler lidar is determined by the statistics of the coherent Doppler signal. The derivation and calculation of the covariance of the Doppler lidar signal for random atmospheric wind fields and wind shear are presented. The signal parameters are defined for a general coherent Doppler lidar system in terms of the atmospheric parameters. There are two distinct physical regimes: one in which the transmitted pulse determines the signal statistics and the other in which the wind field and the atmospheric parameters dominate the signal statistics. When the wind fields dominate the signal statistics, Doppler lidar data are nonstationary and the signal correlation time is proportional to the operating wavelength of the lidar. The signal covariance is derived for signal-shot and multiple-shot conditions. For a single shot, the parameters of the signal covariance depend on the random, instantaneous atmospheric parameters. For multiple shots, various levels of ensemble averaging over the t emporal scales of the atmospheric processes are required. The wind turbulence is described by a Kolmogorov spectrum with an outer scale of turbulence. The effects of the wind turbulence are demonstrated with calculations for a horizontal propagation path in the atmospheric surface layer.

In the conventional microwave mixer it is generally necessary to provide a low-pass filter or some similar network in the intermediate-frequency output circuit. This filter usually takes the form of a capacitance or choke, which is arranged to present, as nearly as possible, a short circuit to the signal and local oscillator frequencies. For a microwave mixer with an IF of less than 100 Mc chokes have been found to be satisfactory provided that a correct choice of the short-circuit position has been made. It is difficult, however, to design a choke system with a capacitance of less than 5 pf and, even at intermediate frequencies as high as 100 Mc, a capacitance of this value could seriously limit the fractional IF bandwidth or the noise performance attainable. At intermediate frequencies greater than 1000 Mc it was expected that the problems of design of a low-pass filter would be even greater because of the dificuity of meeting the conflicting requirements of efficient RF rejection and lF coupling.

This letter presents a low-noise and high-gain CMOS mixer that uses a simple dynamic current-bleeding (DCB) technique. The conventional static current-bleeding (SCB) technique has high conversion gain and low noise figure at a high intermediate frequency (IF) but also has moderately high direct-mechanism flicker noise. Meanwhile, the conventional DCB technique possesses completely opposite characteristics. The proposed DCB technique obtains not only low direct flicker noise and low noise figure at high IF, but also has high conversion gain by combining only the advantageous features of both conventional techniques. Measurement results show a conversion gain of 21.2 dB and a noise figure of 16.3 dB at 10 kHz and 5.6 dB at 10 MHz, while the mixer consumes 4.2 mW at a 1.2 V supply voltage. It was implemented in a 0.11-μm CMOS process with a chip area of 0.8 × 0.8 mm2. © 2017 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:1267–1271, 2017

The indispensable access to real turbulent wake behavior is provided by the pulsed coherent Doppler Light Detection and Ranging (LIDAR) which operates by transmitting a laser beam and detecting the radiation backscattered by atmospheric aerosol particles. The Doppler shift in the frequency of the backscattered signal is analyzed to obtain the line-of-sight (LOS) velocity component of the air motion. From the LOS velocities the characteristic of the turbulent wake can be deduced. The Coherent Doppler LIDAR (CDL) is based on all-fiber laser technology and fast digital-signal-processing technology. The 1.5 µm eye-safe Doppler LIDAR system has a pulse length of 200ns and a pulse repetition frequency of 10 kHz. The speed measurement range is ±50m/s and the speed measurement uncertainty is 0.3 m/s. The 2-axis beam scanner and detection range of 3000m enable the system to monitor the whole wind farming filed. Because of the all-fiber structure adoption, the system is stable, reliable and high-integrated. The wake vortices of wind turbine blades with different spatial and temporal scales have been observed by LIDAR. In this paper, the authors discuss the possibility of using LIDAR measurements to characterize the complicated wind field, specifically wind velocity deficit and terrain effects.

Long versus short pulse width subcallosal cingulate stimulation for treatment-resistant depression: a randomised, double-blind, crossover trial

Observation of a melting layer using a 1.55 µm coherent Doppler lidar (CDL) is first presented during a stratiform precipitation event. Simultaneous radar measurements are also performed by co-located 1.24 cm micro rain radar (MRR) and 10.6 cm Doppler weather radar (DWR). As a well-known bright band in radar reflectivity appears during precipitation, an interesting dark band about 160 m below that in lidar backscattering is observed. Due to the absorption effect, the backscattering from raindrops at 1.55 µm is found much weaker than that at short wavelengths usually used in direct detection lidars. However, the CDL provides additional Doppler information which is helpful for melting layer identification. For example, a spectrum bright band with broadened width and sign conversion of skewness is detected in this case. After a deep analysis of the power spectra, the aerosol and precipitation components are separated. The fall speed of hydrometeors given by CDL is found smaller than that of MRR, with the differences of approximately 0.5 m/s and 1.5 m/s for the snow and rainfall, respectively. To illustrate the influence of absorption effect, simulations of the backscatter coefficient and extinction coefficient of aerosol and rainfall are also performed at the wavelength range of 0.3 ∼ 2.2 µm using the Mie theory.

Ephelides are brown, dotted pigmentation spots that commonly appear on the face. In recent years, picosecond lasers have been increasingly used in clinical practice. Picosecond frequency-doubled 532-nm Nd:YAG lasers (PSNYLs) have been successfully used for treating several common pigmentary disorders among populations with a darker skin type (Fitzpatrick skin-type III-VI).1-3 However, a prospective study with large samples directly comparing lasers with the same wavelength but different pulse widths (PSNYL and its Q-switched counterpart, QSNYL) is lacking. The present study aimed to evaluate the efficacy and safety of PSNYL in comparison with QSNYL for treating ephelides in a split-face manner and determine whether a shorter pulse width is suitable for the treatment of pigmentation disorders. This double-center, prospective, randomized, evaluator-blinded, split-face controlled trial was approved by the Ethics Committee. Two laser devices were used in this study: a PSNYL (Picoway, Candela) and a QSNYL (Medlite C6, Cynosure). The treatment parameters were selected according to each participant's Fitzpatrick skin type, clinical presentation, and endpoint response. The right and left sides of the face were randomly assigned to the QSNYL group and PSNYL group. Standardized clinical photographs were taken for each participant using a VISIA Complexion Analysis System (Canfield Imaging Systems). The photographs were taken before treatment as the baseline and at the 1-week, 4-week, and 3-month follow-up. A blinded evaluation was conducted by three dermatologists. The primary efficacy was defined as the lesion clearance rate at the 3-month follow-up after treatment completion. The lesion clearance rate at the time of evaluation was defined as (number of lesion counts pretreatment−number of lesion counts post-treatment)/number of lesion counts pretreatment × 100%. Seventy-eight participants (74 females and 4 males) were included in this study, and all participants completed the treatment and follow-ups (Table 1). The average clearance rates were 0.773 ± 0.087 and 0.756 ± 0.103 for the PSNYL and QSNYL groups, respectively, with a significant statistical difference between the groups (Z = −2.004; p < 0.05). The photographs before and after treatment are shown in Figure 1. Average VAS scores for the PSNYL and QSNYL groups were 3.64 ± 2.34 and 4.08 ± 2.45, respectively (t = −4.00; p < 0.05). At the 3-month follow-up, three participants (4.05%) still had hyperpigmentation, and one (1.35%) had hypopigmentation. In this study, we adopted a randomized, blinded, and self-controlled method to objectively evaluate the efficacy and safety of PSNYL treatment for ephelides. Similarly, in our previous study, we compared the picosecond and Q-switched alexandrite lasers for treating ephelides and found no significant difference in the lesion clearance rate (0.769 vs. 0.756; p > 0.05).4 Compared with previous studies, this study has a larger sample size and is a two-center study. Melanosomes can more effectively absorb energy from a 532 nm laser, destroying the melanosomes. We used a PSNYL pulse width of 240–400 ps and QSNYL pulse width of 5–20 ns, both of which are significantly lower than the heat relaxation time (50–250 ns) of melanosomes and can effectively destroy the melanin particles in the epidermis. In this study, although there was a statistical difference of the lesion clearance rate between QSNYL treatment groups and PSNYL treatment groups, the two groups showed similar visual efficacy. However, shortening the pulse width has a positive effect; for example, for the treatment of nevus of Ota, a shorter pulse width can improve the efficacy of a single treatment significantly, reducing the number of treatments.5 All authors have read and approved the final manuscript. Y.Y., Z.X., L.G., Y.G., R.Y., and T.L. designed and performed the research study. Q.W., M.Z., R.Z., Y.A., Y.X., and W.W. contributed lesion counts. Y.Y. and Z.X. analyzed the data. Y.Y. and T.L. wrote the paper. CAMS Innovation Fund for Medical Sciences(CIFMS-2021-I2M-1-001). None to declare. This study was reviewed and approved by the Ethics Committee of Hospital for Skin Diseases, Chinese Academy of Medical Sciences Dermatology (No. 2019-LC-015), and that of The Seventh Medical Center of Chinese PLA General Hospital (No. LZEC-2019-QX-008). Clinicaltrials.gov listing: ChiCTR1900028336.

Transcutaneous electrical nerve stimulation (TENS) has been a commonly used modality to relieve aches and pain for over 40 years. Commercially available devices provide multiple therapy modes involving a different combination of frequency and pulse width with intensity. While frequency sets sensation, intensity helps determine tolerability, longer pulse width is reported to induce a feeling of deeper stimulation. In fact, longer pulse width has been empirically shown to deliver current into deeper tissues, but in context of other electrical stimulation modalities. The goal of this study was to unpack the relationship between pulse width and activation depth in TENS. A highly realistic, anatomically-based, 3D finite element model of the forearm was used to simulate the electric field (E-field) distribution, as the pulse width is varied. A typical titration-guided mechanism was used to obtain the strength-duration (S-D) curves of a sensory McIntyre-Richardson-Grill (MRG) axonal model simulating the pain-transmitting A-delta fibers. The pulse widths tested ranged from 30 μs to 495 μs. As expected, shorter pulse widths required more current to achieve activation, resulting in a larger E-field. The S-D curve of the target median nerve indicates a rheobase of 1.75 mA and a chronaxie of 232 µs. When the applied currents are the same, shorter pulse widths result in a smaller volume of tissue activated (VTA) compared to the longer pulse widths. A 21 fold difference in VTA was found between the longest and shortest pulse widths considered. For the conditions tested in the study, an increase in pulse width resulted in an increase in activation depth, exhibiting a linear relationship. Our findings highlight the impact of pulse width on activation depth. While choice of a given therapy mode is usually based on an ad-hoc desirable sensation basis, medical professionals may consider advocating a certain therapy mode based on the depth of the intended target nerve.

Carrier generation and IF signal up-conversion using optical injection locking and stimulated Brillouin scattering

PD06-07 EFFECT OF PULSE WIDTH VARIATIONS ON SACRAL NEUROMODULATION FOR OVERACTIVE BLADDER SYMPTOMS: A PROSPECTIVE RANDOMIZED CROSSOVER PILOT STUDY

Environmentally-safe high-power impulse magnetron sputtering (HiPIMS) technology was utilized to deposit chromium films. This research focused on the influences of the HiPIMS pulse widths on the microstructure of films deposited at different deposition pressures and substrate bias voltages. Under the conditions of the same average HiPIMS power and duty cycle, the deposition rate of the Cr thin film at working pressure 0.8 Pa is slightly higher than at 1.2 Pa. Also, the difference between deposition rates under two pressures decreases with the discharge pulse width. The deposition rate of the short pulse width 60 μs is lowest, but those of 200 and 360 μs are approximately the same. With no or small direct current substrate biasing, the microstructure of films coated at short pulse width is similar to the typical magnetron sputtering deposited films. Elongating the pulse width enhances the ion flux toward the substrate and changes the film structure from individual prism-like columns into tangled 3-point/4-point star columns. Substantial synchronized substrate biasing and longer pulse width changes the preferred orientation of Cr films from Cr (110) to Cr (200) and Cr (211). The films deposited at longer pulse width exhibit a higher hardness due to the reducing of intercolumn voids.