Double-slit experiment (light)

[Royston]

I can't seem to find the right information for a home built double slit experiment (using a laser.) Which, as you've probably guessed, I want to build...on the cheap.

 

So here's a few questions, if anyone can help...

 

What's the most suitable casing, plus material for projecting the light on ?

 

What's the most affordable laser that would suit this experiment ?

 

Where can I get cheap slides and gratings ? I'm pretty sure I saw some on ebay, but I'll have another look.

 

Thanks awfully

[Klaynos]

I can't seem to find the right information for a home built double slit experiment (using a laser.) Which, as you've probably guessed, I want to build...on the cheap.

 

So here's a few questions, if anyone can help...

 

What's the most suitable casing, plus material for projecting the light on ?

 

Casing? And something flat and white.

 

What's the most affordable laser that would suit this experiment ?

 

A laser pen would work, the greater the starting intensity the greater the intensity after the slits, so the more fringes you'll easily be able to see.

 

Where can I get cheap slides and gratings ? I'm pretty sure I saw some on ebay, but I'll have another look.

 

Hrmm, that's a harder one, I've never bought one, thor labs probably sells them but they're NOT in any way cheap.

[swansont]

Where can I get cheap slides and gratings ? I'm pretty sure I saw some on ebay, but I'll have another look.

 

For a buck (plus shipping) you can get grating glasses.

http://scientificsonline.com/product.asp_Q_pn_E_3102563

 

probably available elsewhere, too

[Royston]

It was a very hasty post, so sorry about that (I was just leaving work.)

 

Casing? And something flat and white.

 

I should of mentioned, I want the option to shield light (my pc is in the lounge, if I want to record data.) I'm not sure what I was thinking when I asked that, but most probably the most suitable material, I guess I could use anything (within reason).

 

However, I was also thinking of an ideal material for projecting on to, I must stress, that this is for taking measurements, not just to awe at the wave nature of light

 

A laser pen would work, the greater the starting intensity the greater the intensity after the slits, so the more fringes you'll easily be able to see.

 

I wanted to get something decent (though obviously nothing as expensive as a lab laser), as well as a few laser pens to experiment with different wavelengths.

 

EDIT: Though having said that, I've just found a pointer laser that fits the bill.

 

Hrmm, that's a harder one, I've never bought one, thor labs probably sells them but they're NOT in any way cheap.

 

I just don't want to construct something using razor blades, I need to know I have exact measurements...but you're right, they're not cheap. The majority of places I've looked, sell solely for schools et.c

[Klaynos]

In our optics labs we use a combination of black metal and black card (which is obv faster but more temporary) to shield stray light.

 

As for what to project onto, if you mount a photodiode or similar on a stage that can move sideways at the height of the beam you can effectively scan across the pattern, depending how you mount it you could then easily change the length etc... and it's even feasible to automate the whole thing.

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As for lasers, you wont need anything more complicated than diode lasers, the cheapest and easiest of which is a pointer...

[Royston]

Thanks Klaynos, that's all the info I need.

[DrP]

It is a really cool experiment. Looks like you have what you need, but I was going to support the use of black card with the slits cut into it. And a bog standard cardboard box for the shielding.

[Royston]

I have two 5 mW pointer lasers on their way, (green and red) and I had to settle for two commercial diffraction gratings 200/mm and 600/mm, (I found some reasonably priced ruled gratings, but annoyingly, they didn't accept Switch.)

 

I'm going to experiment with some simple prisms, and make a simple two slit...razor blade method

 

I've contacted a small company that make photodiodes for home use (and are very reasonably priced), and have provided them with a link to here. I just need to construct the casing, which won't be a problem at all, and buy a few colour filters.

 

So my humble lab, is underway. I now need to find a way of converting the charge produced by the photodiode into data on my pc...so I need to give that some thought.

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For a buck (plus shipping) you can get grating glasses.

http://scientificsonline.com/product.asp_Q_pn_E_3102563

 

probably available elsewhere, too

 

Sorry swansont, I missed your post, they're on their way.

 

I remember donning these things a few years ago

Edited March 13, 2009 by Snail
Consecutive posts merged.

[Klaynos]

One nice experiment (which is far far more achievable at microwave frequencies) is if you have a prisim which is TIR'ing and you bring another close to it you break the TIR and get some transmission...

[Royston]

Neat, I'll be dusting off my optics module which I studied last year, and once the parts arrive, and I've built the case (I'm going for something quite robust), then I'm sure there's a lot of experiments which I havn't even considered yet. I'm thinking of experimenting with crystals for instance.

 

The main hurdle, is recording data, i.e an interface of some sort from the photodiode output, into possibly a USB, from a signal converter though I know somebody quite savvy in that area.

 

I will be posting pics in a few weeks, of some of the results I come up with.

Edited March 14, 2009 by Snail

[Klaynos]

Let me find something and send you a pm with a link to the labsheets to the labs I teach... I'll see if I can find the first year ones as well.

[Royston]

So as a USB interface, this seems to fit the bill, and is also very reasonably priced...PicoScope 2200 plus you get free software with PicoScope. This will be more than sufficient for a diffraction experiment, and future experiments.

 

My only remaining problem is what to use between the above, and the photodiode. I just can't seem to find any information on this part of the set-up. Any ideas ?

[Klaynos]

Just a coax connector to a pair of wires should do it.

 

You might do just as well using a 3.5mm mic jack from the computer to the photodiode and then use some oscilloscope software on that, you used to be able to get that kind of thing but it's been a few years since I looked

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Or just use a multimeter with the photodiode which is how our UGs do it.

[Royston]

Again, thanks...I thought it would be something more complicated than a 'wire' for some reason, despite being my initial thought.

 

I guess I had reservations about how the change in charge would be interpreted by the interface/software, but that helps a lot.

[Klaynos]

Oscilloscopes are for the most part just graphical voltmeters...

[Royston]

Oscilloscopes are for the most part just graphical voltmeters...

 

I was more worried about the input, i.e how would the oscilloscope interpret the data from a diffraction experiment, but that's just a failing from me, not fully understanding the maths.

 

Thanks again, I'll just need to go over this, but the equipment is all there now, which should be easy to set up.

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Well I've just been discussing this with the guy I mentioned earlier over a pint, and rather than forking out £150 for Picoscope 2200, he's going to knock up something basic for a few quid, and build a simple app through Max 5, to record the data. If I get more serious later, then I may get something like the Picoscope interface.

 

As per my last post, I just need to wrap my head around the equations that relate a change in potential difference, with the diffraction equations...which would obviously be over distance. Just so I know the data is legitimate.

 

One question came up, is what type of photodiode to use for this, plus I thought of whether an array of photodiodes would work...this will avoid any movement, which may affect the data.

 

Once I have the basic setup, later on I'm thinking of getting parts for a cage, which will be reasonably pricey, but I'll have the luxury of fine tuning in micrometers.

[Klaynos]

The problem with an array of photodiodes is they ALL act differently, I use sets of 2 diodes for my spectrometers and if I just swap the diodes around they show different intensities... So you have to normalise that out, which is quite easy for us, but would be annoying for an array on a diffraction experiment. It does oc depend alot on light levels etc...

[amiya]

you may use the scope software available free (read disclaimer) at http://zeitnitz.de/Christian/Scope/Scope_en.html Its EXCELLENT. Secondly, I guess you need a microscope too to see the interferences. Good luck!

[Royston]

you may use the scope software available free (read disclaimer) at http://zeitnitz.de/Christian/Scope/Scope_en.html Its EXCELLENT. Secondly, I guess you need a microscope too to see the interferences. Good luck!

 

Thanks amiya, but I already have software for that particular application, which is a damn sight better, and isn't free, unsurprisingly. It's possible I could modify any changes via a MIDI for instance, but I'm trying to keep things simple, for the point of the experiment.

 

I've been using MIDI equipment for the last 17 years, so that's one of the first things that popped into my mind when deciding to undertake this...but what you suggested is for audio applications (I don't need the diversion)

 

You guess wrong with the microscope suggestion, but thanks anyway.

 

I've been looking a this http://arduino.cc/en/Main/ArduinoBoardDiecimila, which was a suggestion, plus the input voltage, is variable, despite what I'll be plugging into it will be very small...they're just 5 mW lasers. In any case, once the basic set up is complete, that's when I can start getting fancy, as it were.

Edited March 15, 2009 by Snail

[Royston]

Well I'm not setting up the experiment till next week, been very busy with an assignment, but I thought I'd share some pics (literally after unpacking and dashing to my room armed with the rainbow specs, and my mobile phone...hence the poor resolution)

 

Nothing to write home about I know, but an uber-cheap experiment (thanks to Swansont's suggestion) plus a pic of the laser reflecting off a curve beneath my bedroom mirror. These things have been quite a distraction to my course work

[Kaeroll]

Brilliant! Must try...