Collimationlens

The star should focus down to nice point, with no asymmetric flaring. The overall sharpness of the star image will depend on the magnification and seeing conditions, but it should be symmetrical and perfectly round.

By using a continuous-wave Ti:sapphire laser as a pumping source, we demonstrated a passively Q-switched Yb:YAG laser at room temperature with Cr(4+):YAG as the saturable absorber. We achieved an average output power of as much as 55 mW at 1.03 mum with a pulse width (FWHM) as short as 350 ns. The initial transmission of the Cr(4+):YAG has an effect on the pulse duration (FWHM) and the repetition rate of the Yb:YAG passively Q-switched laser. The Yb:YAG crystal can be a most promising passively Q-switched laser crystal for compact, efficient, solid-state lasers.

Collimationbinoculars

We have developed all-solid-state continuous-wave diode end-pumped Nd:YAG and Nd:GdVO4 lasers that were passively Q-switched by Cr4+:YAG saturable absorbers. The Nd:YAG laser delivered laser pulses with 138 mJ maximum energy and duration of 42 ns, with 3.3 W average power at 1.06 mm for 13.3 W of pump power at 807 nm. An average power at 1.06 mm of 1.4 W was obtained from Nd:GdVO4 under pumping with 7.2 W power at 808 nm. The pulse energy and the pulse duration were 41 mJ and 40 ns, respectively, which correspond to 1 kW pulse peak power. The laser pulses characteristics are discussed for Cr4+:YAG saturable absorbers with different values of the initial transmission.

It is very important to let the telescope thermally stabilize before collimation. A scope that is still cooling down to ambient temperature will produce a heat spike as warm air radiates off the optics. This can distort the star image and make the telescope appear out of collimation when it is not.

After adjusting the screws, be sure to return the star to the center of the field of view by adjusting the position of the telescope. Once the adjustments have been completed, the screws should be snug and the image of the defocused star should appear perfectly concentric, as shown below.

Note: In our experience, the original screws on an SCT secondary mirror are much better to use for collimation purposes than the aftermarket thumbscrews that can be added. Thumbscrews cannot be turned as precisely, making accurate alignment difficult. Also, thumbscrews do not hold the mirror as tightly, increasing the need to collimate more often. Thumbscrews also tend to make people "collimation happy," tending to collimate a scope far more often than necessary. Under normal use, you should be able to go months without collimating a telescope.

CollimationX ray

Defocus the star to produce a donut shape. The hole in the donut is the shadow of the secondary mirror. If the hole is offset from the center of the star, the collimation must be adjusted.

By use of a laser diode as a pump source, a self-Q-switched laser from a Cr, Nd:YAG crystal is demonstrated. The output Q-switched traces are very stable, the threshold pump power is 3.5 W, the pulse duration is 50 ns, and the slope efficiency is as high as 20%. In addition, the pulse width remains constant while the pulse repetition rate varies with pump power.

Collimationradiology

Collimation is critical to obtaining the best performance from your telescope. Aligning the optics of a Schmidt-Cassegrain telescope (SCT) is much easier than collimating a Newtonian telescope and can easily be learned by any user. However, there are some tricks to doing it right, and some things to avoid. If done right, collimation should only be necessary every few months. If you find it necessary to collimate your telescope every few weeks, the mirror is probably not being locked down properly after adjustment.

Collimationin surveying

Collimationmeaning

Now the trick is figuring out which screw to turn. The low-tech trick is to reach up in front of the telescope and stick a finger in front of theaperture. You will see the shadow of your hand in the star image. Move your hand around until it reaches the narrowest (or widest) part of the donut. Take a look at the secondary mirror and see what screw your finger is nearest to (or opposite from). It doesn't matter whether you use the narrow or fat part of the donut, or whether your finger ends up next to a screw or across from one. The only difference will be whether you tighten or loosen the screw.

Whether you tighten or loosen the screw you have found, depends on whether the image is inside or outside of focus. The usual method is to try tightening first and see if the star image improves. Also, note that turning a screw the correct direction will cause the entire star image to move toward the fat part of the donut (upper left in the diagram above). Begin by turning the screw about 1/8th of a turn.

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Collimationin laser

The results in research and development of diode-pumped passively Q-switched Nd:YVO4 lasers are presented with Cr4+:YAG crystal used as an intra-cavity saturable absorber. Using a-cut Nd:YVO4 laser crystals, the passively Q-switched lasers have been successfully developed and provided stable single shortest pulses of 40 ns at the repetition rate of 18.5 kHz, the maximal average output power of 180 mW was achieved corresponding to the optical efficiency of 9% and the slope efficiency of 16%. The dependences of average output power, repetition rate, pulse width and peak power on pump diode power for different transmissions of output mirror are also investigated.

For the star test, use a relatively high power eyepiece. A 10 or 12mm is a good choice for most SCTs, providing a magnification of 200-300x.

Unlike collimating a Newtonian, there are no special tools required for an SCT. However, you will need to test the collimation on a star, so it must be clear and dark. Otherwise, all you will need is a screwdriver to adjust the screws on the secondary mirror.

Collimating an SCT is simply a matter of adjusting the three screws on the secondary mirror. This changes the tilt of the mirror and aligns it with the (fixed) primary mirror. The tilt of the mirror is tested by viewing an out-of-focus star image through the telescope.

Choose a fairly bright (1st magnitude) star for the test. It is important that the star be centered in the field of view when testing collimation. A star at the edge of the field may be distorted, especially at lower powers, and could make the telescope appear out of collimation when it is not.

If tightening one screw makes the collimation worse, return that screw to its starting position and try tightening the other two screws. The most important thing is that the screws end up snug in the end. Try not to loosen a screw without tightening the others to compensate. Leaving the screws loose can cause the collimation to be lost when moving the telescope.