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 2024-11-02 03:44:44

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To avoid the curvature of the earth as impediment, imagine a modulated beam of white light hitting a cubic reflector on a geostationary satellite -no clouds:rolleyes:-

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Thorlabs offers passive laser diode mounts with premounted aspheric optics for collimation or focusing applications. Each of these mounts is compatible with our strain relief and ESD protection cables, also offered below. These mounts are compatible with low-power Ø5.6 mm or Ø9 mm laser diode packages and do not offer active cooling. They can be adapted to standard Ø1" mounts such KM100 Kinematic Mount using the AD15NT Adapter. They can also be mounted in SM1-threaded lens tubes and optomechanics using the AD15F or AD15F2 Adapters.

How far away could you see it in the same lighting conditions without the optics? A simple test to the collimation in this case would be to see how far you can step sideways before it disappeared.

I imagine that with a decent narrow field of view 6" telescope on both ends (send and receive) the light would be visible for a very long ways indeed. I'd wager on the order of 10 miles given ideal viewing conditions (a scope on the receiving end would really help there!). And I'm talking about nothing more exciting than an LED as a light source!

Sure... But you're gonna need a lot further than 200 mile range for that. And if you're interested in optical comm links, why the requirement for white light?

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Example: S-Curve with Rising EdgeThe angle (θ = ftr ) subtended by the beam depends on the signal's rise time (Figure 3) and the wheel's rotation rate (f ), whose units are Hz or revolutions/s. The arc length (Rθ = R ⋅ ftr ) through the beam can be calculated using this angle. For a small Gaussian-shaped beam (Figure 4), a first approximation of the 1/e2 beam diameter (D ),

He stood in our driveway and I started walking down the street to see how far I could see the LED. Just over a mile away the road curved.... The light was still easily visible, mind you, but we lost clean line of sight.

When the blade sweeps through the angle θ , the rise or fall time of the S-curve is proportional to the size of the beam along the direction of the blade's travel (Figure 2). A point on the blade located a distance R from the center of the wheel sweeps through an arc length (Rθ ) that is approximately equal to the size of the beam along this direction.

I do remember though that it was basically impossible for him to manually aim the scope such that I could see it "full time." What he took to doing was slewing the scope through a pattern so that I would see a flash of red every few seconds.

My old college used to send data between campuses using an IR link... that was over a few miles... it had issues with cranes and clouds though...

A chopper wheel, photodetector, and oscilloscope can provide an approximate measurement of the beam size (Figure 1). As the rotating chopper wheel's blade passes through the beam, an S-shaped trace is displayed on the oscilloscope.

Note that I've recently regained interest in this concept for other purposes and am toying with the concept of a pair of quality binoculars. One side of the binocs would be "send" and the other side "receive." The plan calls for a narrow pass visible filter and a carrier frequency (so that a little noise won't kill us). Don't know if/when I'll actually get a chance to try it as I've a lot of other irons in the fire, but it's something for me to ponder.

Estimates seem to vary but it seems that you can see someone strike a match from about 10 miles away (on a clear dark night)

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Figure 2: The blade traces an arc length of Rθ through the center of the beam and has an angular rotation rate of f. The chopper wheel shown is MC1F2.

The SPW301 spanner wrench can be used to install any of our Ø5.6 mm or Ø9 mm laser diodes in the collimation tube. A Ø9 mm laser diode can be directly installed into the tube with the included retaining ring, while a Ø5.6 mm laser diode can be installed with the use of the included adapter kit.

Is there any way to have a 30cm ⌀ source of intense enough white light beam to reach a couple of hundred miles with the least divergence possible, perhaps up to a mile ⌀ ; by 'cheap' methods/lensing/whatever ?

To make this beam size measurement, the combined response of the detector and oscilloscope should be much faster than the signal's rate of change.

The point is that with maybe $10 worth of "optics" we made it such that the naked eye could see a garden variety LED at slightly over a mile away (probably significantly more but we couldn't prove that).

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Laser Diode Temperature WarningPlease note that these collimation tubes do not have any temperature regulation or temperature measurement capability, so we do not recommend using them with higher power laser diodes without additional thermal regulation. Running a laser diode at a high operating temperature can significantly shorten its lifetime.

Figure 3: Rise time (tr ) of the intensity signal is typically measured between the 10% and 90% points on the curve. The rise time depends on the wheel's rotation rate and the beam diameter.

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Camera and scanning-slit beam profilers are tools for characterizing beam size and shape, but these instruments cannot provide an accurate measurement if the beam size is too small or the wavelength is outside of the operating range.

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Note: These cables are not designed to provide any temperature regulation. More information on temperature regulating a laser diode is provided in the Laser Diode Tutorial.

Other Wavelength Ranges and Collimation OpticsThe Laser Diode Collimation Tube is shipped with the aspheric lens (collimation optic) premounted. However, a different aspheric lens can be substituted for better performance at different wavelengths. Any of our M9 x 0.5 threaded mounted aspheric lenses are compatible with the LT110P-B, LT220P-B, and LT230P-B collimation tubes, while any of our M12 x 0.5-threaded mounted aspheric lenses are compatible with the LT240P-B collimation tube. The SPW301 or SPW302 spanner wrenches, respectively, can be used to remove and install these two sizes of aspheric lenses. Please contact Tech Support if you would like to purchase the collimation tube without the aspheric lens, or with a different lens.

includes a factor of 1.56, which accounts for the portion of the beam measured between the 10% and 90% intensity points being smaller than the 1/e2 beam diameter.

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Even a poor job at collimating that would let you see it from further away. People use simple searchlights to shine on to the clouds to attract attention to events.

The best way to collimate a light source, that I've found, is to use mirrors to get it coming out of half a sphere, capturing as much of the light as you can with a lens, use another lens to focus the light onto a very small aperture and then put collimation optics using the aperture as the light source. The smaller the aperture the better collimation you will get but the more light you will loose.

These laser diode focusing packages are similar to our laser diode collimation packages sold above but include an aspheric lens pair for focusing of the laser diode output. The focus can be adjusted by threading the mounted lens pair in or out. These packages are compatible with our SR9 laser diode sockets, available below.

Each model corresponds to one or more of the standard Pin Styles for laser diodes (see the diagram below) and is compatible with our Laser Diode Collimation and Focusing Tubes, Ø1/2" Post Mounts, and Cage Plate Mounts. SR9 models are designed for laser diodes with forward voltages up to 3.3 V, while SR9H models are designed for laser diodes with forward voltages up to 7.5 V. Each strain relief is available with or without a DB9 connector. Models with item #'s that end in -DB9 are pin compatible with many of our Laser Diode Controllers (see the strain relief cable and controller pin diagrams to determine compatibility).

That's not a true white light source though... You can get something that acts like a laser though... super something light source, I'll try and remember what they're called when I'm more awake.

Mounting OptionsThorlabs' Adjustable Laser Diode Collimation Tubes can be secured in a KM100 Kinematic Mount using the AD15NT adapter. Alternatively, they can be mounted in an SM1-threaded mount using our AD15F adapter, as illustrated in the video at the top of the page. However, the outer diameter of the external locking ring on these collimation tubes will not fit in these adapters. As such, the tubes can only be placed into the adapter in one direction, and they will not pass all the way through the adapter. Therefore, the laser diode socket should be passed through the adapter before connection to the diode in the collimation tube. Alternatively, the locking ring can be removed by first removing the tube's end cap. As an alternative mounting option, these collimation tubes can be secured in a KM100V kinematic V-mount.

These strain relief and ESD protection products offer a convenient means of connecting a Ø5.6 mm or Ø9 mm laser diode to many of Thorlabs' laser diode controllers. Each model comes with a laser socket mounted to a small-printed circuit board (PCB). The PCB contains a Schottky diode to clamp any reverse voltages that might appear across the laser diode, as well as a Zener diode to shunt any excessive voltages or ESD away from the diode.

Many years ago my old man had some interest in optical comm links. Blah blah blah. We ran an experiment whereby he made a telescope out of two dime-store magnifying glasses (read: plastic, crappy optics!) and a length of PVC pipe. He put a plain ol' red LED light (powered by a 9V battery) at the focal point.... The idea was that this contraption would quasi collumate the light and allow it to be seen at a much greater distance.

Figure 1: An approximate measurement of beam size can be found using the illustrated setup. As the blade of the chopper wheel passes through the beam, an S-curve is traced out on the oscilloscope.

It is very difficult to collimate non-pointlike sources. It's not that hard to create a source that is diverging enough to be seen a long way away. If you think about if you look up at night and see a plane it is a long way from you but you can see it's non-directional lights, so even a bit of mirroring can help make it brighter. Also the eye is non-linear so will pick out a quite dim light against an even darker background quite easily.

Thorlabs' Adjustable Laser Diode Collimation Tubes are shipped with an aspheric lens (collimation optic) premounted. The position of this lens can be adjusted by up to 2.5 mm (0.1") by rotating the cap on the end of the tube. The position of the lens can then be locked using the external locking ring. Rotation of the cap by 5° corresponds to a linear displacement of the lens by 5.5 µm, and an engraved scale on the actuating cap allows for accurate lens positioning. The lens translates inside the tube without rotation for enhanced pointing stability. The large travel range of the optic ensures that these collimation tubes can be used to collimate any of Thorlabs' laser diodes that emit within their AR coating range. However, the lens in these collimation tubes is not meant to be replaced.