AV Geeks Lunch 3-3-2022

Heat. Heat. Heat. Heat. Heat. Heat. Heat. Heat. Heat. Heat. Heat. Heat. Heat. Heat. Heat. Heat. Heat. Heat. Heat. Heat. Heat. Heat. Heat. Hi everybody, I'm Skip Alzheimer. Welcome to the AV Geeks lunchtime streaming show where we watch old 16 millimeter films. Uh I'm not at the archive. I'm somewhere else. Anyways, uh that first film that we saw, wow. Uh that was probably one of the first Castle films uh made uh made by Eugene Castle and he shot the footage uh or his uh production company did. Later Castle Films of course borrowed and licensed uh from other sources but this was uh original film that uh they did uh and phenomenal film, amazing uh shots. Uh the kids getting uh exposure to that uh lamp so they can get vitamin D. That was uh that was something else. Anyways, uh like I said, we watch old 16 millimeter films and the next film we got set up is an encyclopedia bratannica film about light and dark. And this one is part of a series that kind of teaches some of the concepts of art. So things like texture, things about shadow, uh which this light and dark thing is color, um rhythm, all those things. And so this is uh like I said, light and dark. Enjoy. Art is made of a number of things. Of color, of form of line, of surfaces rough and smooth. of things that are dark, of things that are light, and of the shades and tints that come between. Things that are light and things that are dark. and all the steps between. Something lights against something light and little we can see. [bell] [music] Something dark against something dark and little we can see. [music] [music] Something dark against something light. The thing stands out. The background light. Something light against something dark. The thing stands out oh so bright. In nature we see lights against dark. [music] Dark against dark. [music] and the shades and tints that come between. [music] [music] Make a shadow play with dark forms against the light. Tell a story in your own way. Wood has many shades and tints. Some wood is dark, some wood is light. Dark, medium, light. Put light against dark and dark against light until the contrasts seem to be right. With crayon, with chalk, and with paint, you can make color darker. You can make color lighter. [music] Put darks and lights together in your own [music] way. Make them say what you want them to say. [music] Yeah, there's some interesting scenes there. Um, pretty great film. Not really a uh doesn't feel like an encyclopedia botanica film. Seems like it would have been made for uh Bailey or somebody. Anyways, uh this next film is another one, another Encyclopedia Botanica film. And this one seems like like a it's appropriate. It's how to bend light. And it talks about the concepts of light um and how to bend it with prisms and mirrors and lenses. Enjoy. [music] [music] [music] Light seems to travel in straight lines. Can you prove that it does? Here's a source of light. And here are some cards with small holes in them. If you sight through the holes, you can see the light. In order to reach your eyes, the light travels through the holes in the three cards. If you move one of the cards, the light no longer reaches your eye. The three cards have to be arranged in a certain way in order to see the light. If you thread a string through the holes and pull it tight, you can see that there is a straight line from the light bulb through the holes to the place where your eye was. In other words, the light traveled from the bulb to your eye in a straight line and only in a straight line. We've constructed a room here that's light proof. When the door is closed, no light at all can get in here. Now we'll give light away to get into the dark room. We've set up two spotlights shining at the hole drilled in the wall. The lights are different colors so that you can tell them apart. Green on top, red below. It seems logical to think that some of the light from the green spotlight will go through the hole and hit the far wall inside the room. If that light travels in a straight line, it should make a spot of green light about here. If the light from the red spotlight travels in a straight line, it should hit somewhere up above. Let's go inside and see if that's what really happens. First, we'll have to close the door so that no other light gets in. Yes, it's just the way we thought it would be. A spot of red light above, a spot of green light below. The light is traveling in straight lines. The boy can see the light of that spotlight because the light travels from it to his eyes in a straight line. When the light is not traveling in a straight line to his eyes, he can't see it until it hits something. The light travels from the spotlight to the girl in a straight line. When the light hits the girl, some of it bounces off her face and coat and travels to the boy's eyes. Light from the spotlight is being bent. Does the light that bounces off the girl continue to travel in straight lines after it is bent? We can prove that it does. Does that prove that the light that bounces off the girl continues to travel in straight lines? Light hits the girl and bounces off in all directions. Some of it passes through the hole in the wall. If the bounced light travels in straight lines, then some of it that bounces off her head will go through the hole and hit the inside wall here. And some of it that bounces off her feet will hit here. And that's exactly what has happened. This upside down image proves that the light that bounces off the girl continues to travel in straight lines. This light proof room with a hole cut in one wall is called a camera obscura. The word camera means room and obscura means dark, a dark room. This camera resembles the camera obscura in several important ways. Using small mirrors, we can bend these beams of light so that they are all concentrated at a single spot. Instead of using small flat mirrors, we can use this single curved mirror to concentrate the light. This curved mirror is designed so that it will reflect all the light that hits it to a central point. Here is a larger curved mirror. This one is bending and concentrating light from the sun. The concentrated light from the sun is extremely bright and a great deal of heat is concentrated along with it. This is a cylinder of solid lead. There's another way to bend light besides reflecting it. When light passes from one material to another, for example, when light passes from air to water, it bends. Here's a piece of glass. If we shine a beam of light through it, the light bends. The light bends when it passes from one material to another. Once when it passes from the air into the glass and again when it passes from the glass back into the air. Notice that the light bent by passing from one material to another continues to travel in straight lines after it is bent. Just the same as light that is bent by reflection. This triangular piece of glass is called a prism. Shine light through it and the light is bent. Instead of using two prisms to concentrate the light, we can use a lens. This lens is designed in such a way that every beam of light shining through it is bent just enough to meet at a single point. In other words, the light is concentrated. Lenses are used for many things. One of the most common uses is to magnify something. [screaming] Another common use of lenses is to focus an image. If there is no lens on this camera, there is no sharp image. The lens bends the light that passes through it so that the light forms a sharp image in the camera. [music] Okay, so the next logical step here of course is a film about lasers. And this one was made for the uh US Army and I think it was 1975 and uh this is trying to educate soldiers about um this wonderful tool. And this is before lasers were being used as weapons. And I don't even know if they're being used as weapons now, but uh this was using it for other purposes like targeting and and other types of things that a laser could do. Um and this is an exhaustive film that talks about almost every aspect of laser technology at that point. So enjoy. [music] The word laser triggers fears about death rays, disintegrators, and other beam transported catastrophes. But what we need is truth about lasers, not science fiction. We need to replace unreasoning fear with informed caution so that the full capabilities of one of man's most remarkable inventions can be unleashed in support of the army's mission. More and more weapon systems that incorporate laser functions [music] are being introduced yearly on land and in the air. When certain [music] controls are established and certain precautions are observed, lasers can be used without undue constraint [music] and at minimal risk to personnel so that rational judgments and decisions [music] concerning laser operations can be made in test, maintenance, training, and operational environments. We'll first characterize the nature of laser light, define the actual [music] hazards that are of concern, and then review the controls and precautions that should be established for [music] the safety of all those in a position to be exposed to laser radiation. The laser's capabilities can [music] help multiply the Army's tactical effectiveness in the field. To help achieve that goal, let's now trade silly fiction for hard facts. The facts you'll need to use the laser [music] wisely and safely in the service of the nation. [music] You can think of a laser basically as a light source, but it produces light so different from ordinary light that it's beyond most people's experience. The light we're used to comes from hot bodies like the sun, incandescent light, electric arcs, or electric currents passing through a gas and exciting the gas itself or a coating inside the tube to emit light. As an electromagnetic phenomenon, light is energy and is capable of doing work. Powering a satellite or a light meter, activating the growth cycle in living plants, tanning the skin, starting the process we know as vision by energizing the photo receptors in the retina of our eyes. The eyes serve as detectors for the energy in that portion of the electromagnetic spectrum we label as visible light. We can't detect ultraviolet or infrared wavelengths because the eye is opaque in these regions. But it's the ultraviolet energy from the sun that tans or burns us and from the welder's ark that can damage our eyes and the infrared from the heat lamp that sears us if we fail to take proper precautions. So in this sense there is some hazard from ordinary light and adjacent parts of the spectrum. But it is a fair indication of the extraordinary properties of laser light that for billionth of a second it can achieve intensities many times greater than the sun and is therefore potentially even more hazardous in the absence of suitable safeguards and precautions. Ordinary light energy is spread over spectral bands but lasers concentrate their energies at single wavelengths and so are called monochromatic or single color devices. These characteristics high intensity and monochromaticity together with minimum beam divergence and coherence account for the hazardous nature of laser radiation. These properties arise from the way in which the laser's energy is produced. Light of any kind is produced as electrons are first excited by incoming energy and as they then deexite themselves giving off or radiating energy in the process. The tiny packet of energy involved in both ends of this process is called a photon. The electron can remain in the excited state for a portion of a second before it gives up the energy it has received. This is called spontaneous emission. If however another photon arrives while the first is still excited, the photon is triggered or stimulated to deexite itself instantaneously, producing a second photon that has the same energy, wavelength, phase, and direction of the incident photon. The incoming photon is not absorbed, however, and so there are now two. This process is known as stimulated emission. Under ordinary conditions, the greatest numbers of electrons are in the ground or unexited state and only a small percentage are involved in the spontaneous emission of light. Before stimulated emission can occur, the population must be inverted. That is, the highest percentage of electrons must be in the excited state. This is accomplished by supplying a massive input of energy which in effect pumps enough electrons to the excited state so that the highest number of electrons is in the excited state. This condition favors stimulated emission and results in energy being released. This energy is radiated randomly in all directions in the laser. However, mirrors are added at each end of what now becomes an optical cavity, and they immediately establish a preferred direction for the radiation release by the stimulated emission. A photon cascade now develops along the axis between the mirrors. As the level of energy being produced avalanches upward, this is light amplification. In the laser, one mirror is usually partially transparent and so a large percentage of the amplified light passes through to create the laser beam, but the remainder is reflected back into the cavity to start another cascade. Fully reflected by the other mirror, the cascade traverses the cavity again, constantly building in intensity until it too results in a brilliant pulse of light. Light amplification continues as long as the population inversion lasts. The entire process is called lazing after light amplification by stimulated emission of radiation. Exitation can be achieved by electrical discharge and this can be continuous as in the case of continuous wave gas lasers or this exitation or pumping can be achieved by pulses of highintensity light from flash tubes or other lasers. However it is performed, the exitation and deexitation of electrons is dependent upon discrete energies and frequencies and the output of the laser is directly related to the frequency at which deexitation occurs. In the ruby laser for example, the output wavelength is exactly 694.3 nanome which is red in color. It is important to understand that almost all of the power output of the laser is concentrated at this single wavelength. Power from a conventional light source is distributed over a band of wavelength so that the intensity at any given wavelength is much less than that produced at the same wavelength by a laser. A single wavelength oscillating in a resonant cavity such as that in a laser develops an output that is said to be coherent or in phase both in terms of time and in spatial relationship between waves. This coherence is maintained in the output beam whereas in ordinary light any coherence that is present is lost very near the radiator and the output is said to be incoherent. Additionally, beam divergence in the laser is minimal measured in mills or several seconds of arc. Intensity or more exactly irradiance on the target is strongly maintained. However, the light beam from an ordinary light source spreads rapidly due to spherical radiation and intensity drops off rapidly as well. A very large proportion of the laser's spectacularly high intensity is still present at very long ranges, measurable in kilometers in tactical laser systems. Because of this high energy, the beam may be powerful enough at these long ranges to cause eye damage. And under certain conditions, even reflections can be hazardous. Specular or mirror-l like surfaces change the direction of the beam and retain beam divergence characteristics. Shiny metals reflect virtually all the energy. At angles of incidence nearly perpendicular, glass and plastic reflect a few% and transmit the rest. At grazing angles, very high percentages of the incident energy are reflected from such surfaces as water, ice, glass, and other smooth, glossy, flat surfaces. The point here is that specular reflection should be thought of as containing substantial portions of the energy present in the incident beam. After striking a diffused surface, the hazard associated with reflected radiation is greatly reduced or eliminated since radiation in the initial beam is scattered in many directions. But in spite of this, there may be enough energy left at close ranges to be hazardous. In clear air with strong temperature gradients typified by desert terrain, centilation may create both hot spots and dark spots. The bright spots indicating an intensification of energy present locally in the beam path. Laser reflections from fog, rain, snow, and dust can be of consequence, but mostly at close ranges within approximately 1 meter. Water drops are specular surfaces but they are strongly curved and so dissipate energy effectively due to the highly coherent nature of the laser beam. Interference effects that is the reinforcement and cancelling of reflected energy produce the speckling that is characteristic of laser reflection. Such reinforcement produces locally higher intensities which have been taken into account in the existing protective standards. A final consideration is the fact that lasers operate in different time domains and this affects the energy that is both generated and delivered to the target. As its name implies, power output from a continuous wave or CW laser is continuous. Usually a low power device, the CW laser can nevertheless be dangerous if exposure time at the target is long. Biological effects can accumulate and damage to tissues can result. A pulseed laser delivers its energy in millionth of a second. The total energy is compressed in time and so power density at the target is very high and can be dangerous. The Q switch laser concentrates its full energy in an even shorter time, billionth of a second. Power density at the target increases accordingly and the biological effects can be extremely dangerous. The outputs of pulseed and Q switched lasers can be varied at the desired pulse repetition frequency. In the pulse laser, the state of the cavity remains unchanged and the pulsing rate is established by the rate of firing of the energy source. In the Q switched laser, the lasing action is spoiled or inhibited from completion by blocking the output from the cavity until maximum power is developed at which time the entire quantity is released in a single sharp poke. In this rangefinder, for example, Q switching is achieved by means of a rotating prism. Firing of the energy source is timed so that it precedes the instant at which the position of the prism optically opens the cavity and transmits the accumulated energy. The force of the laser's energy is especially vivid near the output. This laboratory argon laser has its output invisible light and the backs stop of material withstands its force. But the light in the beam acts immediately on sample material. When the energy is focused by a lens, flammable material burns instantly. The lens of the eye serves to concentrate the laser radiation at the retina just as the argon laser radiation is being concentrated at the target by the laboratory lens. It thus becomes easier to understand why lasers can inflict serious damage to the extent of destroying human vision or producing severe burns on the skin at closer ranges. good reasons never to look at a laser beam or its reflections or to intercept it with the hand or body. And we can now see why the use of external optical systems such as binoculars or optical sites aggravates the danger even further, making the user more vulnerable to the radiation. Such equipment should therefore never be pointed into a beam. Given the high intensities and other extraordinary characteristics of laser light and the increasing use in the army of laser devices, the probability of injurious exposure to laser radiation is also increasing. So adequate safeguards must be established for the protection of all personnel who may be exposed. This can be achieved efficiently through the use of the approval safety requirements and guidelines contained in the department of army bulletin control of hazards to health from laser radiation TBM med 279. Comprehensive data are supplied so that relationships between incident illumination, reflectivity characteristics, and biological effects of laser irradiation can be determined and safe operational conditions established. The bulletin and technical manuals for specific laser equipment also provide detailed guidance for safety measures to be taken in dealing with hazards common to electrooptical equipments. This includes explicit data on hazards such as electrical shock, x-rays, cryogenic temperatures, and so on. For the laser beam, safety factors inherent in each formula and equation have been arrived at through scientific studies of the biological effects of laser radiation on the human eye. In general, we can consider that these effects are mainly thermal and the degree to which laser energy will be reflected, transmitted or absorbed depends upon the various properties of the tissue involved. Damage to numerous eye structures can result from laser irradiation and the location of the damage is related to the laser wavelength. Short ultraviolet and far infrared are absorbed primarily at the cornea and the type of damage can range in severity from slight pain to severe pain and clouding of the cornea with obstruction of light entering the eye. Long ultraviolet visible and near infrared energy is refracted at the cornea and lens and absorbed by the retina. Here the degree of damage depends upon where the laser energy is directed. Damage may be minimal as in the case of an oblique beam entrance which causes a lesion in the peripheral retina and may go unnoticed. But if the beam hits the region of critical focusing in the macula or more especially in the phobia, there can be partial but permanent loss of vision. Laser radiation of all wavelengths is partially absorbed by the skin. The effects varying according to energy output. Some lasers are considered non-hazardous while others can cause reactions varying from mild reening to blistering and charring. Although present-day military equipment does not have the power to inflict injury at long ranges, some lasers can cause injury at short ranges. Carbon dioxide lasers, for example, operate at a wavelength that is not transmitted to the retina, but it can still cause corial or skin damage at close range or at high energy. To ensure the safety of all personnel working in laser areas, TBMED 279 should be consulted and its safety requirements observed. All personnel subject to exposure to laser radiation should receive medical surveillance with particular attention given to any change in visual capacity. Warning signs and labels should be used whenever practical to warn personnel of protective procedures required for safety. Government and industry standards have classified lasers into five safety related categories. Class one consists of very low power lasers with completely harmless radiation. Class two consists of low power lasers which require precautions against continuous direct viewing of the beam. Class three consists of medium power lasers which require appropriate protective safety goggles during viewing of the beam. Class 4 consists of high power lasers which can damage the eye or skin of an unprotected viewer. Protective eyewear and clothing are required. Class 5 consists of low, medium or high power lasers which are safely enclosed. As long as the potentially hazardous optical radiation is contained during laser operation, these lasers are harmless. Safety calculations performed according to prescribed procedures should form the foundation for all laser safety and control measures for they take into account the significant variables likely to affect the health and safety of all personnel. Hazard evaluation should be performed for each circumstance in which lasers are to be used so that the controls and safety measures selected actually protect against the potential hazards involved. Both audible and visual warnings and establishment of closed areas may be advisable. For example, in a laboratory or maintenance area where accidental exposure is possible, a countdown before firing may be desirable. Under no conditions look into a laser when it is capable of being fired. Accidental pulsing may occur. Avoid looking into the primary beam. And it is just as important to avoid looking at specular reflections of the beam, including those from lens surfaces. And there are numerous hazards arising from equipment auxiliary to the lasers themselves, such as power supplies. Where voltages are over 15,000 volts, the equipment may produce X-rays. Gas filled tubes or other containers for compressed gases may explode with acoustic energies that may themselves be dangerous. Optical radiation such as ultraviolet light from discharge tubes can be hazardous and toxic gases from materials used in or exposed to lasers can cause serious injury. And lasers sometimes include cryogenic fluids, intensely cold materials which can inflict injury if proper protective gear is not used. Work with lasers should be done in areas of high general illumination so that the iris of the eye closes down, thereby limiting the effect of stray or accidental laser exposure. The laser beam should be discharged into a background that is nonreflective and fireresistant. Areas near the target should be painted black to absorb stray radiation. When exposure levels exceeding those arrived at by reference to TBM Med 279 are anticipated, safety eyewear designed to attenuate laser light to values known to be safe should be worn during firing. The eyewear should be labeled so its specific characteristics can be identified. It is also important to be sure that eyewear designed for specific wavelengths are not used with lasers of different wavelengths. The filter may safely block one but fully transmit the other. In two-sided training exercises in the field employing laser equipment, safety eye protection must be worn by all personnel. For other training exercises, eye protection is required only for personnel downrange within the laser beam path. Calculations should be carried out that define danger areas and the protective areas around them. Suitable safeguards must then be physically established at the test or training site. Personnel must be excluded from the beam path, either direct or reflected, to a distance where beam intensity or beam radiant exposure is within permissible levels. Erection of physical barriers is an obvious means of control. Others include administrative restrictions and carefully controlled limitations on laser beam traverse. It is also essential that all specular reflecting surfaces, even those of a limited surface area be removed from areas close to the laser. Also, all flat, shiny specular reflecting surfaces on the target, such as glass and mirrors, should be masked or removed prior to laser ranging. Standardized personnel safety controls should be exercised at the laser firing position. Only those targets which have a backs stop capable of absorbing or dissipating laser radiation should be ranged on. This may include natural terrain features such as trees and hills or mountains. The backs stop may also consist of man-made features such as earthworks and timber structures. Specular laser reflections from water normally do not require additional range controls for ground personnel. However, it should be recognized that laser energy reflected from water at low grazing angles maintains high energy levels in the downrange path. The physical controls that are established must effectively exclude all personnel from the reflection area. Tracking of non-target vehicular or airborne traffic should be prohibited. And there are certain precautions that should be observed when airborne laser operations are involved as in the case of laser designator and seeker teams. reflection of laser illumination from still water ponds or other bodies of water and substantially horizontal pieces of glass or other flat shiny materials may be hazardous to personnel aloft due to the position of the designator aircraft with respect to the laser beam and its specular reflection. The hazard is less for personnel aboard the source aircraft except when the beam is directed straight down. The geometry of the beam path is such that the beam bounces away in other directions. Consequently, the hazard is greater for those aboard aircraft flying tandem with the designator, those aboard the seeker aircraft, for example. In test and training situations where airborne operations may involve specular reflections from lasers, then consideration should be given to the use of safety eyewear by those in aircraft adjacent to the laser source and flying in tandem. And in all cases, care must be taken to avoid illuminating personnel on the ground. It must be accepted, of course, that the procedures and controls outlined here are applicable for test or training exercises only and may be impossible to accomplish in the tactical environment. In the past few minutes, we have reviewed the basic characteristics of the laser in terms of the safe operation of these powerful and versatile devices. Laser radiation is potentially hazardous because of its high intensity, minimum beam divergence, coherence, and monochromaticity. It is therefore essential to observe the requirements of TBMED 279 before employing lasers in the shop or in the field. Make all required calculations and establish all specified safeguards for the protection of personnel from hazardous laser radiation and from dangers associated with laser support equipment. Never look at the primary beam or its reflections where dangerous levels are anticipated. Wear safety eyewear designed to protect against the specific type of laser radiation. Never allow the laser to be fired under circumstances in which unprotected personnel may be inadvertently exposed. Whether you operate the laser or control its use by others, plan first for safety. And then unleash the laser for all the tasks it is uniquely qualified to perform. All right, all that talk about laser uh uh lasers, we need a break. So, uh, crack open a lucky light. May I point out, beer lovers, that refrigerators are difficult to carry and may contain ordinary beer, while this 12-pack is easy to carry and always contains less filling. Lucky light. Obviously, then one should purchase this 12pack instead of a refrigerator. Thanks for everyone for tuning in today. Um, we'll be back again tomorrow. It'll be another pre-recorded show, but um, this one is this next one coming up is pretty great. There's some cool stuff that I remembered I had digitized at some point and I was like, "Oh, I really want to show this." So, um, if you like what you saw, you can buy some coffee at ko-fi.coms, which is right there. And you can also visit abgeeks.com and see other things that we have done and digitized uh thousands of things. If you like what you saw, you can hit the like button, the thumbs up, uh you can be notified, get a subscribe, all that stuff. Tell your friends. Anyways, we will see you tomorrow. Everybody have a great rest of your day. Take care.