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Measuring Wavelength?

chipdouglas

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I agree with laserman. From reading from the posts some of the test are touting a +/- 70nm? thats not accurate at all. 70 nm takes you from violet to blue. I agree with the if it looks red, hell it's red. Just my opinon.     ;)



michael

edit: "hey look at my obviously violet blu ray, i just tested it and it is 473 nm, who knew"
 



Warske

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Laserman532 said:
[quote author=Warske link=1239067307/0#13 date=1239125268][quote author=Laserman532 link=1239067307/0#10 date=1239122061]If it is for work and precision is important it has to be done one way. If it is ballpark it is done another way. if it is just for grins it can be done the ways listed here.
Why do you think the ways listed here would be less accurate than using a piece of pre-built lab equipment? [/quote]

I will assure you, for a fact they will be less accurate. It is all about resolution, how much resolution do you need to "resolve" your question. ...[/quote]
That isn't actually a reason. You are getting confused between accuracy and resolution. In the long-baseline technique I listed, the resolution is actually infinite depending on how you decide to measure the center of the dots. Think about it. The accuracy is less than infinite, but can be much greater than your lab equipment if you know what you are doing and carefully control the variables. :)

chipdouglas said:
I agree with laserman. From reading from the posts some of the test are touting a +/- 70nm? that's not accurate at all...
Yes, I had mentioned that the toy Hand-Held Spectroscope was 50 or 75 nm. I was referring to using a diffraction grating and a long baseline. Sorry I wasn't more clear.
 

Diode_Virgin

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Warske said:
[quote author=Laserman532 link=1239067307/0#15 date=1239125857][quote author=Warske link=1239067307/0#13 date=1239125268][quote author=Laserman532 link=1239067307/0#10 date=1239122061]If it is for work and precision is important it has to be done one way.  If it is ballpark it is done another way.  if it is just for grins it can be done the ways listed here.
Why do you think the ways listed here would be less accurate than using a piece of pre-built lab equipment?  [/quote]

I will assure you, for a fact they will be less accurate.  It is all about resolution, how much resolution do you need to "resolve" your question. ...[/quote]
That isn't actually a reason.  You are getting confused between accuracy and resolution.  In the long-baseline technique I listed, the resolution is actually infinite depending on how you decide to measure the center of the dots.  Think about it.  The accuracy is less than infinite, but can be much greater than your lab equipment if you know what you are doing and carefully control the variables.  :)

chipdouglas said:
I agree with laserman. From reading from the posts some of the test are touting a +/- 70nm? that's not accurate at all...
Yes, I had mentioned that the toy Hand-Held Spectroscope was 50 or 75 nm.  I was referring to using a diffraction grating and a long baseline.  Sorry I wasn't more clear.
[/quote]

I'll give you a +1 for attempting to debate techniques. But try to "accurately" measure a the width of a human hair with the "resolution" of a plastic ruler from 3 grade. As I said, your experiment is fine for what OP wants to do.
 

Putrio

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Laserman532 said:
[quote author=Warske link=1239067307/0#17 date=1239128387][quote author=Laserman532 link=1239067307/0#15 date=1239125857][quote author=Warske link=1239067307/0#13 date=1239125268][quote author=Laserman532 link=1239067307/0#10 date=1239122061]If it is for work and precision is important it has to be done one way.  If it is ballpark it is done another way.  if it is just for grins it can be done the ways listed here.
Why do you think the ways listed here would be less accurate than using a piece of pre-built lab equipment?  [/quote]

I will assure you, for a fact they will be less accurate.  It is all about resolution, how much resolution do you need to "resolve" your question. ...[/quote]
That isn't actually a reason.  You are getting confused between accuracy and resolution.  In the long-baseline technique I listed, the resolution is actually infinite depending on how you decide to measure the center of the dots.  Think about it.  The accuracy is less than infinite, but can be much greater than your lab equipment if you know what you are doing and carefully control the variables.  :)

chipdouglas said:
I agree with laserman. From reading from the posts some of the test are touting a +/- 70nm? that's not accurate at all...
Yes, I had mentioned that the toy Hand-Held Spectroscope was 50 or 75 nm.  I was referring to using a diffraction grating and a long baseline.  Sorry I wasn't more clear.
[/quote]

I'll give you a +1 for attempting to debate techniques.  But try to "accurately" measure a the width of a human hair with the "resolution" of a  plastic ruler from 3 grade.  As I said, your experiment is fine for what OP wants to do.[/quote]

The resolution is near infinite because the ratio can be as large as you want it to be.  Warske is saying that because the difraction grating splits the beam into multiples, the further your endpoint is from the origin, the further away the dots will be.  To exagerate, if you were a mile away, you could measure within a yard and be very accurate - if you're 30' away and measure to the inch, you will in fact be within 1/720th.  There is no measuring the width of a human hair, at least the way I'm understanding what Warske is saying. Say you use the fixed he-ne beam, and using the difraction grating from 30' away the two dots are 5' 2.25" apart, you know that exact wavelength should be 5' 2.25" apart. You then use your laser, and the dots are say 6' 3.8" apart. Using simple math and google, you can use that ratio to determine your wavelength in a very accurate manner. The further away you go, the more accurate it is. Note, I made those numbers up, but the principle is the same.
 

Diode_Virgin

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Putrio said:
[quote author=Laserman532 link=1239067307/0#18 date=1239130144][quote author=Warske link=1239067307/0#17 date=1239128387][quote author=Laserman532 link=1239067307/0#15 date=1239125857][quote author=Warske link=1239067307/0#13 date=1239125268][quote author=Laserman532 link=1239067307/0#10 date=1239122061]If it is for work and precision is important it has to be done one way.  If it is ballpark it is done another way.  if it is just for grins it can be done the ways listed here.
Why do you think the ways listed here would be less accurate than using a piece of pre-built lab equipment?  [/quote]

I will assure you, for a fact they will be less accurate.  It is all about resolution, how much resolution do you need to "resolve" your question. ...[/quote]
That isn't actually a reason.  You are getting confused between accuracy and resolution.  In the long-baseline technique I listed, the resolution is actually infinite depending on how you decide to measure the center of the dots.  Think about it.  The accuracy is less than infinite, but can be much greater than your lab equipment if you know what you are doing and carefully control the variables.  :)

chipdouglas said:
I agree with laserman. From reading from the posts some of the test are touting a +/- 70nm? that's not accurate at all...
Yes, I had mentioned that the toy Hand-Held Spectroscope was 50 or 75 nm.  I was referring to using a diffraction grating and a long baseline.  Sorry I wasn't more clear.
[/quote]

I'll give you a +1 for attempting to debate techniques.  But try to "accurately" measure a the width of a human hair with the "resolution" of a  plastic ruler from 3 grade.  As I said, your experiment is fine for what OP wants to do.[/quote]

The resolution is near infinite because the ratio can be as large as you want it to be.  Warske is saying that because the difraction grating splits the beam into multiples, the further your endpoint is from the origin, the further away the dots will be.  To exagerate, if you were a mile away, you could measure within a yard and be very accurate - if you're 30' away and measure to the inch, you will in fact be within 1/720th.  There is no measuring the width of a human hair, at least the way I'm understanding what Warske is saying.  Say you use the fixed he-ne beam, and using the difraction grating from 30' away the two dots are 5' 2.25" apart, you know that exact wavelength should be 5' 2.25" apart.  You then use your laser, and the dots are say 6' 3.8" apart.  Using simple math and google, you can use that ratio to determine your wavelength in a very accurate manner.  The further away you go, the more accurate it is.  Note, I made those numbers up, but the principle is the same.[/quote]

accuracy has everything to do with resolution. lets talk practical real world test here

Theory is fine, the practical world is different. sure the further away the endpoint is the further away the dots are with respect to each other...also the bigger the dots therefore finding the center of the dot has everything to do with the resolution of the tool to measure said dot and finding the center of said dot. We got one guy who wants to find out if his laser is red 660 or 635. Your experiment works PROBABLY ok for that. But he said 1nm that is .000000001. You get back to me and let me know how far the wall has to be away from the source to resolve 1 x 10 to the -9 m.

I would find someone with a calibrated monochrometer. Where have I heard that before ::)
 

Putrio

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Ok I don't have a diffraction grating to prove my point, but it can be made with...ooooooooooh man, a DVD.  The spacing between the tracks (d) on a dvd is .74 microns, or 740 nm or .000074 cm (which is what you use in the formula).  Take my newly built blu-ray for example.  Shine it at said dvd at a 45 degree angle.  From a distance (L) of 59.125" to the wall (that's 150.1775 cm) and a dot-dot distance (x) of 36" (that's 81.144 cm) you can calculate using the simple formula wavelength = (x*d)/L that my uncalibrated wavelength is 399.8 nm.  Change the wall distance 1 inch to 58.125" and leave other variables the same and the math comes out at 406.7 nm.  That means at a 5' distance, one inch gives you ~7 nm resolution.  To get 1 nm resolution, multiply the distance by 7 and you have 35', if you can measure to a 1" accuracy.  Calibrate your calculations using the known wavelength of the he-ne laser, use the ratio of measured wavelength to known against the measured of your laser, and you have your wavelength.

The further away you get, the more accurate it is.  Where have I heard that before ::)

Edit* removed unnecessary stuff.
 

Diode_Virgin

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im not that smart enough for all that math. hene looks orange compared to 660, and 635 looks red compared to 660. they all look red compared to blue and green.

I give up...we'll do it your way ;)
 

lasersbee

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IDK... for example... from a single point (X) 60" distance perpendicular from a
flat wall.... a line drawn betweem the two would be 60" long... but.. draw another
line at say 10 Degrees to the left or right eminatimg from that same ponit (X)
towards the same wall.... the line will be much longer... adding to the error...
To compensate that error... wouldn't the wall need to be curved with a radius
of 60" in this example... :-/
Correct me if I'm wrong.... :-?


Jerry
 

pullbangdead

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lasersbee said:
IDK... for example... from a single point (X) 60" distance perpendicular from a
flat wall.... a line drawn betweem the two would be 60" long... but.. draw another
line at say 10 Degrees to the left or right eminatimg from that same ponit (X)
towards the same wall.... the line will be much longer... adding to the error...
To compensate that error... wouldn't the wall need to be curved with a radius
of 60" in this example...   :-/
Correct me if I'm wrong.... :-?


Jerry
No, it's about the angle.  Diffraction happens at certain angles, and the angle is dependent on slit spacing, slit width, and wavelength.  If you're using a wall that is curved like you say, you can use arclength to relate to the diffraction angle.  With a flat wall, you use right-angle trig to relate to the angle, which is easier, and it's easier to find a flat wall than a curved one.  Here's a short explanation in the form of a picture, and it includes a link to a calculator where you can plug in your data. http://hyperphysics.phy-astr.gsu.edu/Hbase/phyopt/grating.html#c2
 

lasersbee

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pullbangdead said:
[quote author=lasersbee link=1239067307/0#23 date=1239148906]IDK... for example... from a single point (X) 60" distance perpendicular from a
flat wall.... a line drawn betweem the two would be 60" long... but.. draw another
line at say 10 Degrees to the left or right eminatimg from that same ponit (X)
towards the same wall.... the line will be much longer... adding to the error...
To compensate that error... wouldn't the wall need to be curved with a radius
of 60" in this example...   :-/
Correct me if I'm wrong.... :-?


Jerry
No, it's about the angle.  Diffraction happens at certain angles, and the angle is dependent on slit spacing, slit width, and wavelength.  If you're using a wall that is curved like you say, you can use arclength to relate to the diffraction angle.  With a flat wall, you use right-angle trig to relate to the angle, which is easier, and it's easier to find a flat wall than a curved one.  Here's a short explanation in the form of a picture, and it includes a link to a calculator where you can plug in your data.  http://hyperphysics.phy-astr.gsu.edu/Hbase/phyopt/grating.html#c2[/quote]
Yeah... it just clicked reading your post... the different dot distances between different wavelengths
are still linear (similar ratio) whether the wall is curved or flat...
Thanks for clearing that up.... and the calculator link...:cool:

Jerry
 

Diode_Virgin

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Wow, just think...all those universities, research institutions, major corporations and scientific institutions who purchased monochormeters and spectrometers when they could have just bought the latest Metalica CD, and they had NO IDEA!!! ;D
 

Warske

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Laserman532 said:
I'll give you a +1 for attempting to debate techniques. But try to "accurately" measure a the width of a human hair with the "resolution" of a plastic ruler from 3 grade.
Thanks for the +1!:)

As to the human hair, that is a different problem, but also very easy to solve: You cut it into 10,000 short lengths, lay them side by side, measure the resulting width with the plastic 3rd grade ruler, and divide the result by 10,000. (Don't ask me to demonstrate this!)

The expensive equipment does many more things, quickly, and in a relatively small area, than just measure wavelength accurately. That is the reason it is so expensive. The hobbyist can often get the measurement as accurately or more so, at the expense of time, effort, convenience, and overworked brain cells.

My point is not to try to prove you wrong, but to point out that once you say something can't be done, you automatically make it true because you stop looking for a solution. One of the things I enjoy about this forum are the number of inventive things people have come up with and shared.

Thanks
 

Diode_Virgin

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I think we spun off into physics and philosophy when the OP just wanted to know if his laser was red or blue...

Great Idea on measuring the hair, I wander what the percentage of error would be with the thickness of the 3rd grade ruler markings.

Also, if you lined up 10,000 hairs side by side and shined a laser through it would it make a grating pattern (like a machida) ;)
 
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Laserman532 said:
I think we spun off into physics and philosophy when the OP just wanted to know if his laser was red or blue...

Great Idea on measuring the hair, I wander what the percentage of error would be with the thickness of the 3rd grade ruler markings.

Also, if you lined up 10,000 hairs side by side and shined a laser through it would it make a grating pattern (like a machida) ;)
Im pretty sure everyone will do a scalp after reading that post.
 

cappernicus

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Laserman532 said:
I think we spun off into physics and philosophy when the OP just wanted to know if his laser was red or blue...
I don't mind tangential debates as long as they're somewhat productive. :)
 

Diode_Virgin

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hey, Warske, not to make a big deal or anything...but how far would the wall have to be away from the source to resolve 1nm using a steel ruler with 1/4" divisions? Not being a smart ass, I am really curious.
 




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