Laser safety / measuring errors question

[chef99]

Homework Statement

a) If you were using a hands –on activity to verify your predictions and use measurements to determine the wavelength of the laser being used, describe any safety precautions you would have to take and sources of error that you might encounter. Be sure to explain how you might reduce the effects of the sources of error.

Homework Equations

n/a

The Attempt at a Solution

First, it is of the utmost importance to be wearing appropriate protective eyewear, meeting or exceeding the minimum optical density protection required for the laser being used. Despite appropriate eye protection, it is still necessary to avoid contact with the laser. This can be achieved through beam path or and/or beam enclosures, and the testing area should be inspected for any glossy or potentially reflective surfaces to eliminate the potential of unwanted reflections, as the light beam could unintentionally reflect into someone's eyes.

The main potential source for error would be slight inaccuracies in measurement, as unless the experiment was done in a vacuum, the light would spread out slightly, making precise hand-taken measurements difficult. A solution to minimize inaccuracies would be to take each measurement multiple times and determine the average.

I'm not sure if the sources of error/how to prevent is right, any feedback is appreciated.

 

[mfb]

The main potential source for error would be slight inaccuracies in measurement

Inaccuracies in measurement of what?
How would the light spreading out influence the measurement (of the wavelength?), and why wouldn't that be an issue in vacuum?

A solution to minimize inaccuracies would be to take each measurement multiple times and determine the average.

That can reduce some but not all uncertainty sources.

To help with the second part, you first have to describe what you measure how, otherwise it is impossible to tell where uncertainties come from.

Concerning the laser safety: There is more you can do, what is necessary will depend on the power of the laser. Make sure it is clearly visible in the room when the laser is on (especially if the laser is outside the visible range), make sure it cannot be switched on unless [whatever safety measure you want], and so on.

 

[chef99]

Inaccuracies in measurement of what?
How would the light spreading out influence the measurement (of the wavelength?), and why wouldn't that be an issue in vacuum?That can reduce some but not all uncertainty sources.

To help with the second part, you first have to describe what you measure how, otherwise it is impossible to tell where uncertainties come from.

Concerning the laser safety: There is more you can do, what is necessary will depend on the power of the laser. Make sure it is clearly visible in the room when the laser is on (especially if the laser is outside the visible range), make sure it cannot be switched on unless [whatever safety measure you want], and so on.

I assumed measurements would be taken by hand, which generally leads to slight inaccuracies, especially if measurements are small (in mm). If a light isn't traveling in a vacuum, does that not increase the chance that it experiences diffuse reflection off of particles that may be present? I could be completely wrong, this is just what I thought.
So for laser safety add the importance of visual warning of the laser being on/off?

 

[mfb]

Measurements of what, using which instrument in which way?

Light can scatter from dust particles, sure, but it is unclear if that has any impact on your measurement. It is not even clear what you measured here.

So for laser safety add the importance of visual warning of the laser being on/off?

Depends on the laser, but in general that is a good idea.

 

[chef99]

Measurements of what, using which instrument in which way?

Light can scatter from dust particles, sure, but it is unclear if that has any impact on your measurement. It is not even clear what you measured here.
Depends on the laser, but in general that is a good idea.

Well, what is measured would probably depend on what the experiment was trying to determine, but it would usually be the distance between the fringes I'd imagine. I thought that if the light was affected by as you say, dust particles or something similar, the light hitting the screen would be diffused, and thus increasing the width of the fringe, which would decrease the measurement from the actual fringe distance. I guess I was making a bit of a generalization in the original answer, but this is really the only thing I could think of that would potentially cause errors in measurement (of the fringes).

 

[mfb]

From your last post I infer that you want to measure the wavelength using a diffraction grating? Why didn't you write that?

Dust can broaden the maxima a bit but it shouldn't shift their central position. It makes it more difficult to find the center - this is an uncertainty you should consider. The properties of the diffraction grating and its alignment will introduce additional uncertainty sources. All these things are impossible to know if you don't describe the setup.

 

[chef99]

From your last post I infer that you want to measure the wavelength using a diffraction grating? Why didn't you write that?

Dust can broaden the maxima a bit but it shouldn't shift their central position. It makes it more difficult to find the center - this is an uncertainty you should consider. The properties of the diffraction grating and its alignment will introduce additional uncertainty sources. All these things are impossible to know if you don't describe the setup.

I apologize for the vague setup, however, I am merely going off what the problem question says. I have mostly been learning experiments using diffraction gratings, so that is really my understanding of these types of setups. I realize now the question doesn't specify the type of experiment, just experiments using lasers in general. I guess the question is asking for sources of error that would be encountered in any experiment? This is partly why I'm having trouble with this question as I don't really know what the sources of error would be unless there are some general sources for all experiments.

 

[mfb]

I guess the question is asking for sources of error that would be encountered in any experiment?

"Errors with everything measured and everything that can influence this" fits to all experiments, but that is not a very useful statement.