LightMachinery (Canada)

Brillouin spectroscopy is increasingly employed for biomedical research and recent advances such as line-scanning configurations further widen the scope of possible measurements. Current spectrometer technologies have limitations which are prohibitive for certain applications. We propose a novel hybrid VIPA-etalon cascade scheme compatible with both confocal and line-scanning geometries. A single VIPA is followed immediately with one or multiple essentially parallel-oriented standard Fabry-Perot etalons of approximately matching thickness. The cascaded etalons preserve near-unity throughput while increasing the contrast by more than 20 dB per stage. Other advantages include simplicity, compactness, and wavelength flexibility. We present simulations of the hybrid VIPA-etalon scheme and an experimental proof-of-concept measurement.

This article talks about a way to make wood better by heating it at high temperatures between 180-240 °C. By doing this, the wood becomes more stable and lasts longer. The article focuses on a specific method called ThermoWood technology.Scientists made a 3D computer model to understand how heat and moisture move inside the wood during the heating process. They used special equations to describe these changes and made sure their model worked by comparing it with real-life experiments. The article explains that the model and the ThermoWood heating method could help create better wood products, and the scientists hope to do more research on this in the future.

The discharge in a repetitively pulsed TE gas laser begins its lasing cycle by being homogenous in nature but quickly (10s of ns later) transitions into filamentary mode due to plasma discharge instabilities. The filamentary discharge transitions into an arc mode which presents a very low impedance path for the pulsed power circuit. Hence the current is weakly damped and continues to oscillate (resonance) until all of the circuit energy is dissipated. This post lasing remnant circuit energy causes electrode erosion and contamination of the lasing gas. Ideally, all of the initially stored energy must be deposited in the homogenous discharge at the optimum pumping intensity but due to the plasma discharge instabilities it is very difficult to avoid the filamentary arc discharge mode. Therefore, an effort is made on reducing the intensity of the current flowing through the discharge and pulsed power circuit in the post-lasing stage (late currents). A snubber circuit is deployed across the main energy storage capacitor in the pulsed power circuit to dissipate a portion of the remnant circuit energy. The snubber circuit consists of a series string of HV diodes and a series resistor. The diodes become forward biased when the storage capacitor voltage reverses polarity and allows current flow through the snubber resistance which dissipates energy. An optimum value of the snubber resistance was experimentally confirmed. The maximum amount of energy dissipated in the snubber is ultimately constrained by mutual induction effects between adjoining loops.

High spectral resolution lidars (HSRLs) designed for aerosol and cloud remote sensing are increasingly being deployed on aircraft and called for on future space-based missions. The HSRL technique relies on spectral discrimination of the atmospheric backscatter signals to enable independent, unambiguous retrieval of aerosol extinction and backscatter. NASA Langley Research Center is developing a tilted pressure-tuned field-widened Michelson interferometer (FWMI) to achieve the spectral discrimination for an HSRL system. The FWMI consists of a cubic beam splitter, a solid glass arm, and a sealed air arm. The spacer that connects the air arm mirror to the main part of the interferometer is designed to minimize thermal sensitivity. The pressure of the sealed air-arm air can be accurately controlled such that the frequency of maximum interference can be tuned with great precision to the transmitted laser wavelength. In this paper, the principle of the tilted pressure-tuned FWMI for HSRL is presented. The pressure tuning rate, the tilted angle requirement and challenges in building the real instrument are discussed.

*† ‡ § An experimental study of the aerodynamics of an airship that is envisaged to operate at high altitude for a long duration flight is presented. The study employs a novel approach experimental to the investigation of high altitude airship aerodynamics. This approach, which employs the use of a water-towing tank to examine the full-scale aerodynamics on a sub-scale model, is described. The effects of wind speed, crosswinds and appendages on the aerodynamics of the airship are assessed from measurements of forces and moments. Flow visualization studies are also presented to clarify the effect of the flow conditions on the effectiveness of the control surfaces.