Thinner membrane types come in rolls or as integral parts of building materials. Common examples include polyethylene sheeting and aluminum- or paper-faced fiberglass roll insulation. Another type is foil-backed wallboard. Most paint-like coatings also retard vapor diffusion.

How to make abeam expander

Drawing upon 30 years of international design and manufacturing experience Optical Surfaces Ltd. indicated that the required high performance and design compactness was best achieved through an off-axis parabolic beam expander. Benefiting from a stabilised manufacturing environment Optical Surfaces was able to supply a compact x15 off-axis beam expander unit with a transmitted wavefront accuracy of lambda/5 over the complete 150mm output aperture measured at 633nm. The high surface quality of the optics virtually eliminated any limitation on the performance of the LIDAR system due to telescope feedback.

Each off-axis beam expander is housed in an aluminium housing with provision for fixing to an optical table. Alignment aids are provided to ensure correct beam pointing. Standard beam expanders have fixed magnification. Variable magnification beam expanders can be supplied with interchangeable primary mirrors. An interferogram and OPD map is supplied with every beam expander manufactured by Optical Surfaces.

In future it is planned to exploit the achromatic performance of the optical system, making multiple wavelength DIfferential Absorption Lidar (D.I.A.L.) measurements in this Doppler mode where species concentrations and the wind field can be simultaneously monitored with the same equipment.

Keplerianbeam expander

Your home may not need a more effective vapor retarder than the numerous layers of paint on its walls and ceilings unless you live in extreme northern climates. "Vapor barrier" paints can be an effective option for existing homes in colder climates. If the perm rating of the paint is not indicated on the label, find the paint formula. The paint formula usually indicates the percent of pigment. To be a good vapor retarder, it should consist of a relatively high percent of solids and thickness in application. Glossy paints are generally more effective vapor retarders than flat paints, and acrylic paints are generally better than latex paints. When in doubt, apply more coats of paint. It's best to use paint labeled as a vapor diffusion retarder and follow the directions for applying it.

In mild climates, materials like painted gypsum wallboard and plaster wall coatings may be enough to impede moisture diffusion. In more extreme climates, higher-perm vapor diffusion retarders are advisable for new construction. They perform best when installed closest to the warm side of a structural assembly -- toward the interior of the building in cold climates and toward the exterior in hot/wet climates.

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The development of a pulsed coherent LIDAR system potentially was theorised to offer clear air detection over a distributed corridor to several kilometres range and not suffer from terrain induced clutter. The DERA design was based upon being able to build a compact and high performance monostatic system in which the same LIDAR telescope transmits and receives the laser signal.

Beam expander

Optical Surfaces Ltd. have collaborated with the Remote Sensing Group at the Defence Evaluation and Research Agency (D.E.R.A., Malvern, UK) and the Civil Engineering Department of Salford University (Manchester, UK) to develop high performance off-axis beam expanders for integration into a new generation of pulsed coherent LIDAR systems.

Spot size

The DERA site at Malvern has been involved in the development and theoretical understanding of remote sensing applications for over 30 years. With a considerable in-house expertise in theoretical physics and engineering staff familiar with building instruments, DERA have been involved in notable remote sensing projects with the UK MOD, European Space Agency, Aerospace Companies and University Research Departments.

Coming ready aligned the DERA team was able to simply and rapidly integrate the variable focus (infinity to 20 metres) beam expander into the LIDAR unit. Further future operational flexibility was built-in as the off-axis beam expander design gave completely achromatic performance from the infrared to the visible.

Beamdivergence calculator

In most U.S. climates, vapor barriers, or -- more accurately -- vapor diffusion retarders (vapor retarders), should be part of a moisture control strategy for a home. A vapor retarder is a material that reduces the rate at which water vapor can move through a material. The older term "vapor barrier" is still used even though "vapor retarder" is more accurate.

Vapor retarders are typically available as membranes or coatings. Membranes are generally thin, flexible materials, but also include thicker sheet materials sometimes called "structural" vapor retarders. Materials such as rigid foam insulation, reinforced plastics, aluminum, and stainless steel are relatively resistant to water vapor diffusion. These types of vapor retarders are usually mechanically fastened and sealed at the joints.

The ability of a material to retard the diffusion of water vapor is measured in units known as "perms" or permeability. The International Residential Code describes three classes of water vapor retarders:

Gaussianbeamcalculator

Vapor retarder installation should be continuous and as close to perfect as possible. This is especially important in very cold climates and in hot and humid climates. Be sure to completely seal any tears, openings, or punctures that may occur during construction. Cover all appropriate surfaces or you risk moist air condensing within the cavity, which could lead to dampened insulation. The thermal resistance of wet insulation is dramatically decreased, and prolonged wet conditions will encourage mold and wood rot.

Except for extensive remodeling projects, it's difficult to add materials like sheet plastic as a vapor retarder to an existing home. Obtaining an energy assessment and thoroughly sealing any leaks it reveals is are very effective for slowing moisture movement in and out of your home.

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Beam ExpanderThorlabs

The LIDAR system was developed to measure phenomena involved in local wind fields and the dispersion of atmospheric pollution in built up city areas. In this demanding application the LIDAR directs an eye-safe pulsed CO2 laser into the atmosphere. Naturally occurring aerosol particles in the air backscatter the laser radiation and this is detected by the LIDAR receiver. The Doppler shift between the out-going and backscattered light is evaluated thereby giving the line-of-sight velocity of the aerosol scatterers which can be assumed to move with the localised wind field.

Effective moisture control in these areas and throughout a home must also include air-sealing gaps in the structure, not just the use of a vapor retarder. How, where, and whether you need a vapor retarder depends on the climate and the construction of your home.

Laser beam

Operating at 120 pulses per second (500 nanosecond pulse length) the DERA LIDAR system has been able to routinely measure the wind velocity and the aerosol concentration to a range of 3 km with a range resolution of approximately 100 meters.

Optical Surfaces laser beam expanders incorporate off-axis mirrors which provide an unobstructed output and highly efficient transmission.The reflective design of these beam expanders is achromatic and with aluminium coatings can operate from UV to far IR without adjustment. Optical Surfaces beam expanders are portable and can be used without the need for internal re-alignment.

Water resistive barriers are generally placed around the perimeter of the building just under the exterior finish, or they may actually be the exterior finish. The key to making them work effectively is to permanently and carefully seal all of the seams and penetrations, including around windows, doors, electrical outlets, plumbing stacks, and vent fans.

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Missed gaps of any size not only increase energy use, but also increase the risk of moisture damage to the house, especially during the cooling season. A water resistive barrier should also be carefully inspected after installation before it is covered by other work. If small holes are found, they may be repaired with caulk or polyethylene or foil tape. Areas with larger holes or tears should be removed and replaced. Patches should always be large enough to cover the damage and overlap any adjacent wood framing.

An air barrier/vapor retarder attempts to accomplish water vapor diffusion and air movement control with one material. This type of material is most appropriate for southern climates where keeping humid outdoor air from entering the building cavities is critical during the cooling season.

The task of having to try to measure the dispersion of airborne pollutants in a built up city environment along a clear air corridor necessitated the development of the new generation of pulsed coherent laser radar (LIDAR) system. Traditional techniques including radar and continuous wave (c.w) LIDAR were found to have notable shortfalls in trying to solve this problem. Whilst c.w LIDAR offered good spatial and spectral resolution, such systems typically measure wind velocity and turbulence at a point in space and are limited to a few hundred metres detection range. Radar was eliminated as a measurement tool mainly due to the clutter experienced close to a built up environment and the lack of clear air returns.