请问哪里可以找到"HE-NE激光器的同轴指示原理与设计"的论文

eline · 发表于 2003-4-8 02:48:00

谢谢了.

thales · 发表于 2003-4-8 07:01:00

External Mirror Laser Cleaning and Alignment Techniques
Lasers for Which These Procedures Apply
The following was developed for a typical 100 mW external mirror argon ion laser (henceforth referred to as ’’Argon’’). It will, of course, also be suitable for a krypton ion or mixed gas laser. See the section: Maintenance, Alignment, and Modifications of the ALC-60X Laser Head for specific information pertaining to that laser (and the Omni-532) AFTER reading this set of instructions all the way through.
This technique also works for copper vapor, CO2, 2 mirror YAG, and many other types of external mirror lasers including all similar type home-built lasers. It will also be suitable with obvious modifications and simplifications for lasers with an internal HR and external OC.

(Note that what follows includes a more sophisticated version of the general procedure described in the section: Major Problems with Mirror Alignment for sealed internal mirror HeNe laser tubes. However, the basic principles are similar.)

If you already have a working argon laser or *green* HeNe laser, you can do red HeNe lasers. These are aligned at the factory using the 488 nm or 457 nm lines of an argon laser. Hold up an unpowered (red) HeNe tube so a light shines down its bore and you will usually see a deep blue light transmitted through the mirrors. This is what we’’re going to use to our advantage. This technique was developed the hard way after discovering the techniques described by those who write laser books are not exactly tested in the lab and often written by someone who has graduate students to do it for them. The ’’Cards with Crosses’’ technique only works on lasers that are nearly aligned. The approach described below works on anything including newly installed tubes that are not yet centered in their cradles as well as for very short lasers.

My (Steve Roberts) thanks to Dale Harder at HH Laser Refurb for teaching me this neat little trick for initial mirror alignment. Dale is the ultimate prefectionist. His lasers exceed their specs.

It’’s also the only technique for low gain lasers short of an autocollimator or factory computerized search mode alignment jig.

This technique works on the fact that the optimized dielectric mirrors used in laser cavities are often largely transparent or only partially reflective at wavelengths at least 100 nm away from the design wavelength.

Mirrors within a milliradian (mR) of parallel is a hard angle to achieve, and that’’s what you are shooting for.

Moral: Once it’’s aligned and tweaked, don’’t mess with it!!

THE AUTHOR OF THE FOLLOWING ASSUMES NO RESPONSIBILITY FOR YOUR ACTIONS OR SAFETY. LASERS ARE FRAGILE, DANGEROUS, EXPENSIVE DEVICES. PROCEED AT OWN RISK!!!

IF YOU ARE NOT COMFORTABLE WITH ATTEMPTING THIS OR THINK YOU ARE DOING SOMETHING WRONG, GET SOMEONE TO DO IT FOR YOU, THE GENERAL FEE FOR THIS AVERAGES $100 to $200 AN HOUR PLUS MATERIALS!!

SAFETY: NEVER look down the bore of the laser you are aligning if it is under power. While extremely unlikely, all the wrong circumstances could converge to result in it lasing when you don’’t expect it! (There is also some UV from the discharge which isn’’t good for you.) When power is off, there is no danger except from the alignment laser beam passing all the way through the bore. Electrically, there is no risk of shock with all covers in place. But if adjustments need to be made inside, there could be exposed high voltage terminals. It is essential to unplug the power supply from the wall outlet and confirm that its main filter capacitors are fully discharged and/or disconnect the umbilical cable before touching anything inside the laser head. The ignite/start card capacitors can also hold a charge which isn’’t dangerous but it wouldn’’t hurt to check them just the same. The last thing you need is to be startled in the midst of delicate optics! Also see the general info in the section: Laser Safety and for ion lasers in particular: Argon/Krypton Ion Laser Safety.

Required Equipment and Other Stuff
Alignment jig or optical table (described below).
A 5 to 7 mW HeNe laser with clean beam (henceforth referred to as the ’’HeNe’’).
A fluorescent orange (preferred) or yellow sticker (get these from office supply companies).
A long thin sewing needle.
A lab jack or custom made HeNe mount to set the beam height of the HeNe (see below).
If you will be cleaning the optics (which is probably a good idea while you have the laser partially disassembled and assumed below, see the section: Chemicals and Supplies.
The Alignment Jig
I can’’t afford optical benches on my budget. I needed a long bench to work on my lasers. The solution was to go to the local aluminum company and see what they had in the computer as leftovers from a larger sheet that was cut to order for a customer. A 1/4 thick 3.5 foot long 14 wide piece of T6061 polished on one side was $40. A 16 foot piece of 1 x 1 finished square stock was 25 dollars.
Drill and tap the 1x1 stock every six inches and screw the plate to it with the stock along the long edges so an end view looks like this:
[]___________[]

If you do it right, this will turn out to be very strong and stiff, as well as flat from end-to-end and side-to-side.

At one end, drill the mounting hole pattern to mount your argon laser head via the screw holes in its baseplate. Make the holes oversize to give you some play in aligning the laser.
Initial Bore Alignment
The next step is aligning the HeNe. You need to make a mount for the HeNe if you don’’t have a lab jack to adjust your HeNe up and down. A real lab jack is around $200, so I improvised. I made a T shaped or cross shaped jig out of a piece of 1 wide 1/4 aluminum bar stock, with a piece of U channel screwed down along the long way to hold the HeNe head. The HeNe is taped to this and then tied with cable ties. At each of the three ends of the cross I used a 2 inch long 1/4 80 threads per inch screw with a steel ball tip as a foot. So by adjusting the three screws I can raise lower and tilt the HeNe till it goes cleanly down the argon bore. These screws are available from Thorlabs or Newport or other optical supply companies as complete assemblies with mounting bosses that bolt into the aluminum, no tapping required, for about $15 each. My prototype used good old #6 machine screws at first, but then I upgraded to the fine screws as they are much more stable.
This design is shown in Alignment Laser Three Screw Platform. See: HeNe Laser with Reflected Dot for a photo of this assembly in use.

Stick a fluorescent sticker over the HeNe output, turn on the HeNe and very carefully use the needle to poke a small hole where the center of the beam hits the sticker.
WARNING: High voltage inside HeNe head.

DANGER: Class III HeNe beams hurt or cause damage if you get it in your eye. Orange stickers tend to improve the contrast of the reflected HeNe beam, and they glow when the argon starts to weakly lase, enhancing your chances of getting it working.

Carefully remove the mirrors from your Argon at both ends, after checking to see if there’’s any sort of beam - even if it is very weak. If it’’s lasing at all, you just need a optics cleaning!!! If the tube is misinstalled or the beam grazes the tube, that is another chapter as well as if you just have dirty optics. If it is aligned well enough to lase DON’’T unalign it!!! See the section: Walking the Mirrors in External Mirror Lasers to tune the resonator for maximum power and best beam quality.

Get a very clean quiet place to work. Send the kids to the movies or out on a date. Send the dog and cat away. You want a sterile, hospital clean environment without disruptions. Relax - this can take hours the first time. If your laser is one of the ones that need a 5/8’’s inch wrench to adjust mirrors, you need that too. Wash your hands with hard soap, the liquid soaps leave a emolient on your skin that messes up optics - skin oils eat the coatings off the optics and polymerize when the beam hits them. The Intracavity beam is thousands of time brighter then the output beam, and it will burn the optics.
Watch out for stray beams that come off the Brewster windows!!!!!
DANGER: Class III and Class IV power levels, use laser safety precautions appropriate for your laser. When your Argon is lasing, terminate its beam on a proper beam stop where you can’’t see the blocked beam. A cumulative exposure to a medium power reflection can cause eye damage.

DANGER: DO NOT stare at diffuse or specular reflections!!!!

Set the removed mirrors on a very soft clean cotton cloth coating down. This keeps dust off the coatings. Remember which mirror was where as one is the ’’output’’ and the other is the ’’high reflector’’. Most lasers will lase the same with the mirrors reversed though some have tapered bores with a preferred direction. The Output Coupler (OC) mirror is usually slightly concave with a spherical figure. Depending on the length of your laser, the radius of curvature may be anywhere from 45 cm (e.g., ILT-5490) to several meters (large-frame multiwatt). The ALC-60X would typically use a 60 cm optic OC. The High Reflector (HR) mirror is usually flat (though some lasers may use what’’s called a ’’confocal’’ configuration with both mirrors curved with a focal length (f = 1/2 the radius of curvature) equal to the distance between them). The curvature aids in creating a specific beam size and divergence and helps compensate for drifts in alignment. Believe me, aligning two flat mirrors and keeping them lasing is very tough. Though this configuration gives you more output power, it’’s not worth the fight to keep them aligned.
Note that if you substitute optics from another laser, the curvature(s) and reflectance (for the OC) may differ substantially. Attempting to align a laser with incompatible optics may be much more difficult or impossible and the maximum power could be greatly reduced even if you can get it to lase. Just because you can physically swap mirrors between lasers doesn’’t mean they will work!

Set the HeNe on the optics table, power it up and align it so it goes down the argon bore, through both Brewster windows, and then hits a white card. If you see arcs or rings of light on the card, you are grazing the inside of the bore. Work the hene mount till you get a clean dot. This can take a while. Keep the HeNe as far away from the argon as possible so you have room to work. The farther away, the better the alignment. You are making an optical lever to aid in seeing mirror deflections. DO NOT MOVE OR BUMP THE HENE TILL THE ARGON IS LASING!!!!!
You are now ready to deal with the Argon:
I am assuming you have the output end of the Argon facing the HeNe.

Cleaning the Optics
The following applies to lasers with external mirrors. For internal mirror HeNe and Ar/Kr ion tubes, only the outer surface of the OC needs to be cleaned and this is a lot more forgiving than the optics inside the cavity.
Old lasers often have a lot of dirt in them despite the O-ring seals, and getting rid of this dirt is a major concern as you don’’t wish to burn it into your optics. (Recall that there will be light flux with from 10 to 100 times the output power of your laser bouncing back and forth between its mirrors depending on its size and optics (e.g., 5 to 200 WATTs of circulating flux for 100 mW to 20 W ion lasers). It’’s a judgement call as to when this is needed. I (Steve) could not figure out how to provide general guidelines on this.

See the section: Cleaning of Laser Optics for additional information including the required chemicals and supplies, WARNING about soft-coated optics, and other Web sites with optics cleaning procedures.

These two steps will be repeated for each optic surface (starting with the Brewster windows):

Take a swab, wet it with acetone, let it set a moment, then flush it with more acetone. Wipe it from the top of the Brewster Window down-word with a rolling motion. You want to just scrub the optic. This takes some pressure, but be gentle. Do exactly one pass with each swab and then discard the swab. Break it in half so you do not accidentally reuse it. Do this 2 to 3 times and then let it dry and examine the window with a bright light for residual dust and films. Use lens tissue if very dirty, otherwise use swabs. Use gravity to your advantage to get the contaminants to flow downward.

Repeat the above with Methanol till clean. Acetone kills grease, methanol cleans the surface.
Now repeat the same procedure on the high reflector mirror until clean and let dry. However, the coated mirrors are MUCH less robust than the quartz Brewster windows - be gentle! Clean the back side of the optic as well as the face, as contaminants migrate.
DO NOT clean any optics mount rubber O-rings as these will contaminate the optic with byproducts after the laser heats up if cleaned with other then distilled water.

Aligning the Rear Mirror
Install the high reflector (HR, rear mirror) into the far end of the Argon making sure the coatings face inward.
Slowly adjust the optics mount screws so that the weak REFLECTED HeNe beam from the front coated surface of the Argon HR mirror is visible on the face of the HeNe, then carefully walk the HeNe beam so it is right back into where it came from. If this is really good, the HeNe will flicker from you canceling out lasing with a third mirror, but this is rare. Note that each mirror will reflect 2 beams, 1 from the front and one from the back of the optic. You want the one off the coating. Note also the Brewsters may generate more reflections as well. You will end up with a bunch of dots dancing on the HeNe, keep track of the one you want. Keep working until you have a stable tight mirror mount with the beam centered in the hene beam. then back off some slack to leave room for adjustments of the screws, and recenter the beam. You’’re WORKING with FRESNEL reflections, or about 2 to 3 PERCENT of the HeNe beam - a few hundred microwatts at best - so turn off the room lights to see the weak beams.

HeNe laser with reflected dot shows the HeNe alignment laser on its 3-point adjustable mount. The reflections of the HeNe beam from the mirror being aligned on the argon laser (off of the lower right corner of the photo, not shown), can be seen on the fluorescent sticker. In this case, the mirror still needs some more work!

Aligning the Front Mirror
Clean the FRONT Brewster window using the two step procedure described in the section: Cleaning the Optics, above.
Carefully install the FRONT mirror (nearest the HeNe) after cleaning both sides using the same procedure.

Carefully align it using the rear mirror procedure, above.

Powering up the Argon - Final Alignment
Making sure you have proper cooling for the argon laser, leave the HeNe on and switch the Argon ON and turn the tube current up to the upper limit, then back it off a little. This should be About 9 amps if you have a 10 Amp maximum laser. Let the laser warm up. DO NOT EXPECT IT TO LASE AT THIS POINT. If it does laser you are very lucky or you have a large frame (e.g., 1 meter long) laser.
VERY SLIGHTLY loosen the rear mirror mount, NOT THE MIRROR ITSELF!! and slowly press it against the Mount holder or REAR PLATE of the laser, rock it back and forth slightly while doing this, you will see a small flash of laser light on the HeNe face.

WARNING: THIS PROCEDURE IS FOR LASERS LESS THEN 250 MILLIWATTS ONLY. For bigger lasers, see the vertical search procedure in the laser manual or use the fine adjust screws or search bar!!! This flash will tell you which way you have to move the mirror mount screws, usually opposite of the way you have to hold or tilt the mirror.

Once you have it steadly lasing, see the section: Walking the Mirrors in External Mirror Lasers to tune the resonator for maximum power and best beam quality.

If you don’’t get a flash, repeat the alignment procedure until you get it!. This take patience and time. Commercial laser optics have a small amount of wedge to avoid creating ghost beams which interfere with the lasing process. This wedge may be what is messing you up as you may be trying to align the incorrect reflection!

Walking the Mirrors in External Mirror Lasers
The following applies to external mirror lasers where the mirror adjustments at both ends are accessible and permit small, precise, repeatable changes in alignment to be made easily.
For a laser tube without screw adjusters but with compliant mirror mounts, see the section: Walking the Mirrors in Internal Mirror Laser Tubes for a modified (painful and risky) procedure that applies to common HeNe and argon ion internal mirror lasers.

If your laser produces any sort of beam and the alignment of both mirrors independently is optimal (either after testing and/or after correcting it as described in the sections starting with: External Mirror Laser Cleaning and Alignment Techniques then its time to optimize the output power and beam quality by adjustments to both mirrors.

Indications for the need of further alignment include:

Output power with proper excitation (e.g., tube current) is significantly less than expected based on tube specifications and there is no evidence of other physical problems (like contamination of the gas fill, or dirty or). damaged optics).

The beam profile is not perfectly circular and Gaussian (assuming it is supposed to be TEM00).

There are beam artifacts like off-axis arcs, rings, spots, or fuzzy areas. (However, a single weak spot or row of spots is probably just due to the OC having some ’’wedge’’.
See Effects of Walking the Mirrors for an exaggerated (hopefully!) illustration of why this happens. As can be seen, although the mirrors may be perfectly parallel to each other and there is still some output, by not being aligned with the bore/capillary, portions of the beam are cut off, less than the full amount of gain medium participates in the lasing process, and there can be reflections from the walls and other structures in the tube to create artifacts.
For external mirror lasers with fine adjustment screws on the mirror mounts, the Walking the Mirrors procedure isn’’t really at all difficult and can usually be performed quickly and painlessly without much risk of losing the beam entirely.

For all measurements of output power, a laser power meter is highly desirable. It doesn’’t need to be fancy since maximizing power is what’’s important, not an accurate value. Anything that will convert photons to a meter reading will be fine including the absolutely trivial ones described in the sections starting with: Sam’’s Super Cheap and Dirty Laser Power Meter. It’’s just that your basic allotment of eyeballs isn’’t very good at detecting small changes in intensity! :) Note that mode cycling of your HeNe tube will result in small variations in output power - these can be annoying but need to be mentally discounted in determining the maximum power output readings.

Power up the laser let it warm up at the power level (if relevant) that you will be most interested in using.

If you haven’’t just cleaned and aligned the optics (the HR and OC mirrors independently), do so before attempting the mirror walking procedure since it assumes that the each mirror has been adjusted for maximum power. And, if the optics are dirty, you will just have to do this all over again at a later time!

While monitoring output power, turn the X adjustment screws only by the same small increments in each direction to maximize the reading. Once X is peaked, go to the Y adjustment screws and do the same. DON’’T go back and forth and NEVER allow the beam to disappear entirely!!! If your laser has three-screw adjusters (at 120 degrees from one-another), just do all three, again optimizing each pair before proceeding to the next.

Perform a few iterations of this procedure and power and beam quality should converge to the best that is possible.
That’’s it! Now, if you aren’’t totally obsessive-compulsive, you will lock down the mirror adjusters and get on with your life. :)

zhhy · 发表于 2004-6-6 22:15:00

you mei zhongwen fanyi a

dsq1980 · 发表于 2004-9-2 07:08:00

不是吧

请问哪里可以找到"HE-NE激光器的同轴指示原理与设计"的论文

请问哪里可以找到"HE-NE激光器的同轴指示原理与设计"的论文

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