Introduction: Measure Wavelength of Laser Cursor.

Shinning a laser pointer thru a microscope calibration grid (0.1mm spacing), I was pleased to take in an noise pattern projected connected the opponent wall. In this instructable we will take or s measurements and attempt to calculate the wavelength of my laser arrow.

Supplies

Laser pointer - low world power

Microscope Calibration Ruler surgery Diffraction Raspy.

Tape measure

Television camera

Step 1: Setup the Experiment

Mount the diffraction grating (with known spatial arrangement) vertically some distance from a fence in. Aim for sufficient distance so that the beaming floater in the interference pattern are adequately separated. Grid spacing will increment with distance, but may become also dim to distinguish. Make positive your diffraction grating is collateral to the surface being projected to.

Mount a target of proverbial dimensions on the wall, this will be the projection aeroplane. I misused a bright paper public square measuring 98.2mm happening from each one side.

Measure the distance from the grating to the projection plane. In my setup the distance was 649mm.

Shine the laser thru the grating so that a clear interference pattern is visible connected the target. Capture an image of the target connected a camera. (Hold the camera at the same height A the direct so that you'atomic number 75 not tilting the camera up or down, a sideway aspect is the only way to capture the image without block the light, but try to minimise this angle as far as possible.)

Footmark 2: Measurements

Admissive your image in a Paint program.

We know the dimension of the target, utilization the paint program to measure the width of the fair game in pixels. For much truth measure at the homophonic pinnacle as the silver spots.

In my case this was 818 pixels = 98.2mm

Then using the same method measure the distance in pixels between the centers of adjacent refulgent spots.

I got 37 pixels.

Straightaway calculate the distance 'tween the center of the fulgid floater.

37 is 22.108 multiplication smaller than 818, the distance represented away 37 pixels is 22.108 multiplication littler than 98.2mm.

37pixels = 98.2mm/22.108 = 4.44mm

Tone 3: What Are We Calculating?

The bright spots on the target result from constructive interference, or when the perch waves arrive in phase angle. The dark spots in 'tween are a resultant of destructive incumbranc, or when the light waves are not in phase, 180° out of phase for the center of the dark spot.

Looking the first bright spy like a shot tail the poin, it is easy to see paths a and b are the Same distance, so the illuminated arrives in phase angle and we hold constructive interference.

Now imagine a bit where the light meets that is squirming towards the left of the image starting from the first bright spot, paths a and b will set off to differ in duration, until we get to where the broken lines meet, this is the darkest spot. At this point path b is exactly half a wavelength thirster than itinerary a. the light waves arrive 180° out of phace.

If we continue moving left we reach the next bright spy. Here I called the paths c and d.. way of life d is precisely single wavelength longer than way of life c. If we can calculate the lengths of these paths and take off them we would possess calculated the wavelength of our optical maser pointer.

Stone's throw 4: Pythagoras

EDIT: I give birth made a silly fault, the values in the figures above should live 4.39mm and 4.49mm.

The spatial arrangement of the slits id 0.1mm, the first bright spot sits in the middle, 0.05mm.

One side of our triagle is 649mm as measured, the top side is 4.44mm - 0.05mm = 4.39mm

Using Pythagoras we know h1 is the square root on the sum of the other sides square.

Likewise manipulation geometry to calculate the sides of the triangle for h2.

giving us Lambda (wavelength) = sqrt(649^2 + 4.49^2) - sqrt(649^2 + 4.39^2)

Step 5: Google It!

type

sqrt(649^2 + 4.49^2) - sqrt(649^2 + 4.39^2)

into Google and we get our answer 0.00068411341

but remember all our measurements were in mm, thus we need to divide by 1000 again to pay off our answer in meters.

And then final exam solvent is 684nm

Which when compared to actual wavelengths , as wel Googled, sits nicely within the range for red light!.

Step 6: Alter It Raised

Repeat the experiment and try to calculate the absent parameter.

For example, apparatus the experiment an unknown length form the target and try to calculate it.

OR use a grating with different spatial arrangement and try to calculate information technology from the other measurements. etc

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