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Introduction to an optics lab

1. Your safety

Apart from usual laboratory hazards, such as high voltage, toxic chemicals, or dumb co-workers, there is a specific one relevant to optics: lasers. The power of typical laboratory lasers ranges up to 20 Watt which is probably less than your reading light. Which means that the horrors you’ve seen in sci-fi movies are greatly exaggerated and the worst a laser beam can do to your skin is a minor burn you may even wish to proudly show to your friends. However, there is one part of your body that is especially vulnerable: your eyes. If a direct laser beam of more than a few milliwatt power hits your eye, your eye will get permanently damaged. The main rule is therefore

Never look directly into the laser beam!

To make following this rule easier, it is strongly recommended that you wear safety goggles whenever a laser is on. Now, since you are not going to wear them anyway, at least try to follow the suggestions below:

Familiarize yourself with the type of lasers used in your room: continuous or pulsed, visible or invisible, repetition rate, pulse energy, power, color, whatever is relevant.

Avoid positioning your eyes at the level of the laser beam. If you drop something, close your eyes or look away from the table while bending.

Avoid or be well aware of laser beams flying around above their usual height or shooting straight up. Keep visitors out when a hazardous beam configuration is present.

Remember, by hurting your eyes you will not just damage your health, but also your colleagues may have to suffer a shutdown of experimental activities and a lengthy investigation.

2. Equipment care and maintenance

Every little optic in your lab costs a few hundred dollars. If it doesn’t, it probably costs a few thousand dollars. So, exercising proper care is essential.

Avoid touching optical surfaces with your fingers. If you do happen to touch something, however, this is not a tragedy. Just clean the optic immediately with acetone using one of the standard techniques. Much worse if you don’t notice / forget / neglect  to clean it, your body fat residue will enter a chemical reaction with the glass surface and damage it permanently in a few hours.

Familiarize yourself with the turn-on and shut-down procedures. Best of all, hang them on the wall and check yourself every night before leaving. You don’t want to come back next day and discover your setup burnt or flooded.

Use latex gloves to handle unmounted optics, e.g. to place an optic into a mount or remove it. Store all unmounted optics in original boxes.

Avoid burning objects with the laser beam (sounds like a fun idea doesn’t it?). The smoke will condense on your optics and fog them. In particular, be careful about blocking laser beams with black carton.

If you remove an optic and lay it on the table, don’t leave any optical surface facing upwards, even for a few minutes. You’ll be surprised to see how much damage even a brief exposure to dust can do. 

Do not eat, drink, or smoke in the lab.

Don’t be ashamed of your errors. A furious boss won’t kick you out for a scratched mirror! It is normal for beginners to make mistakes, and the cost of the equipment you will damage is already planned into your lab’s budget. It would be much worse if you hide your errors and your team spends days, weeks, months trying to figure out what’s wrong with the setup.

3. Good experimental practices

Mark all optics, both the element itself (pencil on the cylindrical side surface) and the mount (sticker). The information you write should be sufficient to track the item down to the original purchase order, but also to identify it quickly in the lab.

Decide consciously whether to use high-end or cheap optics/hardware for a particular location. Avoid combining high-end mounts with low-end posts.

Always close the door to the lab. Air movements and temperature gradients disturb your alignment.

Make sure your laser beam is well centered on all optics. Never use partial beam blocking for attenuation.

Attach your optics carefully with screws or magnetic mounts. Do not leave any items in use unattached, even temporarily. Do not use excessive force when screwing, unless exceptional stability is required.

Don’t lean on or against the optical table. Holding on to the overhead rack is ok.

If you are aligning an optic, let go of a knob after turning it. Holding a knob displaces a mount a bit.

You may want to keep the lights off when aligning. Darkness will inspire your creativity and also enhance the sensitivity of your eyes.

Do not track your beam with chewing gum wraps and old ripped newspapers. Use library cards and carton screens instead.

Light travels a foot in an nanosecond. Easy to remember.

If you lose alignment of a laser cavity, the main rule is – don’t panic! If you start turning all the knobs randomly, you’ll only make it worse. At best take a half an hour brake and ponder a safe recovery procedure.

Keep good records of your activities – unless your name is Hendrick Schön or you envy his fame (he comes from Konstanz too, by the way)! Record not only the data you take but also all major changes of the setup, procedures developed, problems encountered and the ways found to solve them. Spend some fifteen minutes a day doing this. It is a good investment: your notebooks will cost a few thousand dollars each once you win a Nobel prize!

Most of the data acquisition nowadays is computerized. Which means (a) hardware failures happen when you are least prepared so frequent backups are imperative and (b) you have to store your data in a way that would allow one to find a necessary file quickly. By experience, it is better to avoid file names like P-t-InP-001-2_1-surf-MBE-circ.dat. Instead, use a date-based file nomenclature and record the conditions of each dataset acquisition in your notebook.

A final note

Approach your supervisor with healthy skepticism. Remember that he is what you will be in a few years. He might be more experienced, but not any smarter! Besides, you are much more familiar with your setup and don’t have three more projects and a lecture course to take care of. Although it might be a good idea to listen what he/she has to say, always evaluate his ideas critically. Remember that it’s your, not his way into science that you are paving!

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