Alvium series by Allied Vision - alvium

 2024-11-23 11:00:24

Fresnellensuses

Many companies were involved in the development and refinement of the Fresnel lens. Some supplied only the glass for the lenses, either in rough form, or both cast and polished. Other companies assembled the glass elements and performed finish work on the lens elements. Still other companies produced both the glass and the finished lenses. This story will be divided into several parts, each discussing one or more of these companies and their contribution to the development of the Fresnel lens.

Another key process note is to consider the fill volume in the e-beam application because we find that the melt level of a material in the crucible directly affects the success of the crucible liner. Overfilling the crucible will cause the material to spill over and create an electrical short between the liner and the hearth. The outcome is cracking in the crucible. This is the most common cause of crucible liner failure. Placing too little material in the crucible or evaporating too much material before refilling can be detrimental to the process as well. When the melt level is below 30%, the e-beam is likely to strike the bottom or walls of the crucible which immediately results in breakage. Our recommendation is to fill the crucible between 2/3 and 3/4 full to prevent these difficulties.

This calculator is for estimation purposes only. The estimated mass is that needed to produce a desired film thickness (1 micron in this case) on a flat substrate at a point directly above the source, accounting for the approximate plume distribution of the selected source type. It does not account for any expected nonuniformity in thickness over a larger substrate area. More complex geometries, e.g. those with offset and/or tilted sources, may have higher material requirements. The estimated mass is for the film deposition only; additional margin should be included to account for loss during ramp-up, burn-in, stabilisation and ramp-down.

Due to the high vapor pressures of both zinc and sulfur at low temperatures, zinc sulfide is usually deposited in a dedicated vacuum chamber.

The first National Lighthouse Lens Survey was released in 2001 at the Sixth Maritime Heritage Conference in Wilmington, N.C. It listed more than 400 classical Fresnel lighthouse lenses in the United States, and two pre-Fresnel, Winslow Lewis lenses. The inventory was a compilation of databases researched by Mike Vogel of the Buffalo Lighthouse Association and the American Lighthouse Coordinating Committee, and by Al and Helen Gademsky of Ohio.

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Most lighthouse enthusiasts think that the Fresnel lens was the first lens used in lighthouses. However, that assumption is incorrect in that a number of lenses were proposed and put into use in the years before Augustin Fresnel designed his famous lens. This story will give you information about these early attempts to use lenses to augment the power of lighthouse optics.

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Below is a listing of the major changes in the Fresnel lens through time and in most cases who the creator of each change was.

* This is a recommendation based on our experience running these materials in KJLC guns. The ratings are based on unbonded targets and are material specific. Bonded targets should be run at lower powers to prevent bonding failures. Bonded targets should be run at 20 Watts/Square Inch or lower, depending on the material.

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The fill rate above assumes that the material is fully melted and does not take into account packing density. It should be noted that the crucible liner may need to be loaded multiple times, pre-melted, and topped off in order to achieve the final desired melt level/fill rate. When loading the crucible, do not load more than 80% of the height of the crucible liner.

Another alternative is to change crystals frequently and ignore the error. The graph below shows the % Error in Rate/Thickness from using the wrong Z Factor. For a crystal with 90% life, the error is negligible for even large errors in the programmed versus actual Z Factor.

We recommend to sweep the e-beam at low power to uniformly melt the material and avoid hole drilling. Evaporating at a low e-beam power will also help to avoid material dissociation. Pressure should be monitored to ensure outgassing is at an acceptable level before increasing power. With an evaporation temperature of ~800°C, we anticipate a deposition rate of 10-15 angstroms per second. It is important to note that zinc sulfide decomposes at the source and recombines at the substrate only if the substrate temperature is adequate and nucleation occurs. Substrate surface cleaning is required for good adhesion. Yttrium oxide (Y2O3), hafnium oxide (HfO2), or fluorides can be used as a thin adhesion layer if necessary.

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Zinc sulfide can be e-beam evaporated from a tantalum or molybdenum crucible liner. However, thermal evaporation is more commonly used for depositing optical films because stoichiometric films are easier to obtain using this method.

Zinc sulfide is an inorganic chemical compound with a chemical formula of ZnS. It is white in appearance with a melting point of 1,700°C, a density of 3.98 g/cc, and a vapor pressure of 10-4 Torr at ~800°C. It is often used as a phosphor and can emit various colors depending on the element introduced as an activator. It is evaporated under vacuum for infrared optical coatings, more specifically, night vision optical coatings.

The French Commission for Lighthouses was established on April 29, 1811. In 1819, Arago who had become a member of the French Commission for Lighthouses in 1813, offered to make a systematic review of possible improvements in lighthouse illumination. He requested that Claude Mathieu and Augustin Fresnel be assigned as his coworkers on the project. His request was granted on June 21, 1819, and Augustin agreed to serve on the committee.

Fresnel lenses represent a unique aspect of U.S. Coast Guard history. These artifacts are highly sought by a wide variety of museums and associations. Due to their historic significance, fragility, high value and the U.S. Coast Guard’s policy to protect and preserve these artifacts, an additional set of conditions is placed upon prospective borrowing organizations. Requirements for the care, security and display of Fresnel lenses are as follows:

Due to the high vapor pressures of both zinc and sulfur at low temperatures, zinc sulfide is usually deposited in a dedicated vacuum chamber.

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The German government etched symbols onto the prisms of their Fresnel Lenses. This is the story of those symbols. The German government marked most of their lenses with a government certification symbol. Before 1933 and the Nazi Reich, the symbols used were the German Imperial Eagle and a symbol that looked like a castle, which represented the German Seamarks Service. These marks were etched onto the lens glass to certify that the lens met the requirements for government usage.

Instructions for use: Input the Crucible Liner Volume, Select Material (if not available in menu, manually input Material Density in g/cm3), and input fill rate %.

The English and Scottish lighthouse authorities wanted to produce all Fresnel lenses and other lighthouse equipment in their own country and persuaded the Cookson Glass Company to begin production of Fresnel lenses in 1834. Cookson brought in Leonor Fresnel, Augustin’s brother, as a consultant and produced Fresnel lenses from individual pieces and prisms as done by the French lens companies. The first of these better designed Fresnel lenses, built by the Cookson Co., was installed in Scotland in 1835, in the Inchkeith lighthouse.

Pressure should be monitored to ensure outgassing is at an acceptable level before increasing power. With an evaporation temperature of ~800°C and a base pressure of 10-6 Torr, we anticipate a deposition rate of 10-15 angstroms per second. It is important to note that zinc sulfide decomposes at the source and recombines at the substrate only if the substrate temperature is adequate and nucleation occurs.

Some years ago Chad Kaiser of the US Lighthouse Society ran across a photograph of what was supposed to be the most powerful lighthouse in the world at 1 billion candlepower. Yes, that is billion not million. I became intrigued and started researching this light and its history. This story will describe this very unusual lighthouse in France and how it came to be. It is actually not a true lighthouse at all. Instead it is an example of one of the earliest and most powerful Airway Beacons ever built. But, first we need to understand a little more about air

Instructions for use: Select source type, input distance from source to substrate and Select Material (if not available in menu, manually input Material Density in kg/m3).

Unfortunately, Z Factor and Shear Modulus are not readily available for many materials. In this case, the Z-Factor can also be determined empirically using the following method:

We recommend thermally evaporating zinc sulfide from a tantalum boat such as our EVS8B005TA. A tantalum baffle box like our EVSSO22 may also be used. Thermal evaporation is more commonly used for depositing optical films because stoichiometric films are easier to obtain using this method.

KJLC recommends a fill rate between 67-75%. Overfilling the crucible will cause the material to spill over and create an electrical short between the liner and the hearth causing the crucible to crack. Placing too little material in the crucible or allowing the melt level to get too low can be detrimental to the process as well. When the melt level is below 30%, the e-beam is likely to strike the bottom or walls of the crucible which immediately results in breakage.