Aligning the Laser Beam

Monday, Thursday and a long day on Friday were devoted to aligning the beam on the 4 inch focal length laser on mirror #2 and #3. This is a time consuming and careful process that involves a number of minor, sometimes counteracting, adjustments working in tight spaces. In the end the beam was very well aligned and several lab mates were satisfied with the quality of their jobs after the alignment.

Here are the lessons learned:

1. Don't rely on the red beam.

To save time on frequently closing the side doors and lid for every laser test pulse, as well as being able to see the beam, I decided on Thursday to just try aligning the red beam. This proved to be frustrating as I was stuck with the beam slanting down and to the left. The beam cross section quality was also uneven and diffuse. After a phone call with a Boss technician he convinced me to abandon the idea of practicing/aligning on the red beam and just go back to pulsing the actual laser. Following this advice produced useful results on Friday (described below).

2. Big movements early and small adjustments late

The 3 directional adjustment knobs on the mirror mount are for up/down, left/right, and diagonal from upper left to lower right. There is no lower left to upper right knob. Once the burn spots become within about 1 diameter of each other, pare down the twist amount on the knobs, or else you run the risk of overcompensation, thus backtracking on progress.

3. Take an indirect route

For example, if you see that the downstream beam is high and right of the upstream beam, instead of using the diagonal knob, consider using the up/down and left/right to achieve the same effect. Or use all 3 knobs. The more knobs you use, the more likely you are to achieve a three dimensional adjustment that will get you to the target beam location.

4. More layers, less tape.

Convention calls for 2 layers of masking tape and frequent tape changes. More time efficient and more informative is to make a 3 layer tape and put more spots on it before a change out.

5. Clean before align

If you use a triple layer, this will also help minimize any char residue from the tape after pulsing that would require a re-cleaning of a mirror.

6. Protect the assets.

At the very start when you may have no idea what direction the beam is going. construct a protection board to block stray beams from hitting the microelectronics, wires, cables and the keypad control board components at the front right of the machine. This probably only needs to be in place for the first few pulses and can then can be removed once you are certain that pulses will land on the tape.

7. Side doors

Remember to close the side doors for safety before pulsing the beam, as the interlock is only on the main top lid.

8.  Loosen all the way

The set collars on the adjustment knobs should be loosened all the way back to the knob itself while making adjustments; the collar tends to creep forwards when messing with the knob. When you are aligned, remember to retighten the collar flush to the mount to secure the position. Use your other hand to hold steady and firm on the knob head while spinning the collar back to its lock down position.

Progress of alignment tests going from top to bottom

It is dark inside the nose cone

a useful head mounted flashlight

O-ring out of position and burnt through

Lens Cleaning

1. Throw them a curve

It is difficult to see from a side view which side of the lens is curved. Here is a trick to get it right. Position yourself directly under a long fluorescent light tube on the ceiling. If the reflection of the tube is thin and you can make out the details of the shape, that is the curved side. If the white reflection is broad and covering most of the lens, that is the flat side.

2. Especially for you

We now, under Taylor's guidance, are using a specially formulated lens cleaning liquid in a dispenser bottle that comes with it. Also, we are no longer using the one-time disposal Fluent brand wipes to clean lenses or mirrors, nor are we using any type of rubbing alcohol.

3. It's a drag

Do not swirl the lens tissue or cleaning wipes; this will only recirculate any particles on the lens surface. Drag in one direction instead, that'll remove particles and debris.

4. Blind it by the light

Wear a headband mounted flashlight to work on the nozzle when loosening or tightening the retaining ring. Otherwise it is hard to see inside the recessed column of the nozzle.

5. Mom says so: trim those nails

to avoid scratching mirrors and lens, even if you have gloves on!

6. A gentle push

The black O-ring between the retaining ring and lens easily moves out of position. Try to coax it, often multiple times, back into position while turning the retaining ring. Do this by taking a Fluent brand wipe, rolling one corner to make a thin cone shape, and use the tip of the cone to move the black O-ring around.

7. Spin the cone

This may better than turning the ring tool when loosening/tightening the retaining ring.

8. No Trespassing

Unless absolutely necessary, do not touch the Zoom ring right above the silver exterior spring. Moving this will cause auto-focus to be off.

9. No head banging

When spinning the nose cone back on the air flow tube, stay clear of the mount head attached to the gantry. That head is very sensitive to alignment to even the gentlest force/bang/knock.