Deg Rms Research Articles

FPGA-Based Optical Cavity Phase Stabilization for Coherent Pulse Stacking

Coherent pulse stacking (CPS) is a new time-domain coherent addition technique that stacks several optical pulses into a single output pulse, enabling high pulse energy from fiber lasers. We develop a robust, scalable, and distributed digital control system with firmware and software integration for algorithms, to support the CPS application. We model CPS as a digital filter in the Z domain and implement a pulse-pattern-based cavity phase detection algorithm on an field-programmable gate array (FPGA). A two-stage (2+1 cavities) 15-pulse stacking system achieves an 11.0 peak-power enhancement factor. Each optical cavity is fed back at 1.5kHz, and stabilized at an individually-prescribed round-trip phase with 0.7deg and 2.1deg rms phase errors for Stages 1 and 2, respectively. Optical cavity phase control with nanometer accuracy ensures 1.2% intensity stability of the stacked pulse over 12 h. The FPGA-based feedback control system can be scaled to large numbers of optical cavities.

Design, Analysis, and Optimization of an Acute Stroke Gait Rehabilitation Device

Stroke is one of the leading causes of adult physical disability, and rehabilitation and hospitalization costs for stroke are among the highest for all injuries. Current rehabilitation techniques are labor intensive and time consuming for therapists and difficult to perform effectively. Research suggests that starting rehabilitation during the acute or subacute stage of recovery results in better outcomes than therapy delivered in the chronic stage. To improve the gait rehabilitation process, robot-assisted gait rehabilitation has gained much interest over the past years. However, many robot-assisted rehabilitation devices have limitations; one of which is being bulky and complex to handle. Large and expensive devices that require special training to operate are less attractive to clinics and therapists, and ultimately less likely to be available to patients especially at the early stage of stroke. To address these limitations, this research proposes a new gait rehabilitation device called the linkage design gait trainer (LGT). The device is based on a walking frame design with a simple four-bar linkage “end-effector” mechanism to generate normal gait trajectories during general walking and exercise. The design of the four-bar linkage mechanism was optimized for a particular gait pattern. A prototype of the device was developed and tested. The kinematics of the device itself and gait kinematics with and without assistance from the device were recorded and analyzed using an optical motion capture system. The results show the linkage mechanism is able to guide the leg of the user during over ground walking. There were some differences in the hip (20.5 deg RMS) and knee (14.8 deg RMS) trajectory between the person walking with and without the device assistance. The study demonstrated the concept and feasibility of this novel gait training device.

Model Attitude Determination in Wind Tunnel with a Luminescent Paint Data System

The question is addressed how registration targets in luminescent paint images can be used to determine model position and attitude (P&A) of the test article in a wind-tunnel test. The theory for such P&A determinations is developed and applied to data from a pressure-sensitive paint test in Arnold Engineering Development Center’ s 16-ft Transonic Wind Tunnel. It is shown that the camera system is capable of resolving pitch and yaw angles to within 0.005 deg rms. However, systematic differences as large as § 0.05 deg are found between the camera-based angles and angles determined from a sting-mounted balance. By analyzing the motion of the cameras relative to thetunnel walls, the observed discrepancies may beexplained by rotation of the cameras relativeto the test article. In some cases, these rotations are clearly correlated to operating conditions of the tunnel.

Determination of Verdet constant from combined ac and dc measurements

Two methods of determination of the Verdet constant (V) for an optically transparent medium are described. These methods use the same apparatus in which the intensity of a monochromatic beam of light is modulated by passing it, successively, through a polarizer, the medium under test (contained within a solenoid which carries ac of frequency f in its windings), and an analyzer. The emergent beam is incident on a detector which produces a steady output voltage Uo for the special conditions of the optical system set for maximum transmittance and, simultaneously, zero modulation. Methods I and II, which were tested by determining V for water for the wavelength 643.3 nm, are based, respectively, on the ratios u1/Uo and u2/Uo, where u1 is the rms value of detector output voltage varying at frequency f and u2 is the corresponding output varying at frequency 2 f. The three mean values of V from method I, method II, and a literature survey agree to within 1%. The standard deviation in the values of V by method I (eight determinations) is 0.8% of the mean and by method II (16 determinations) is 1.4%, leading to respective standard errors of the mean (attributable to random errors) of 0.3% and 0.4%. By either method there is, additionally, 0.4% systematic uncertainty in V arising from calibration accuracy of the instrumentation. The total range of Faraday rotation angles studied spanned the range 2×10−4–0.24 deg rms.