- #1
Lauri
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I’m looking to demonstrate destructive optical interference using a laser pointer. I’m splitting the beam with a prism and projecting the beams onto one point on the wall. Somehow I’m failing to get any effect, however.
Setup:
1. I’m using a static laser pointer, a prism and a handheld mirror. The laser is at 0cm, the prism is at 7cm, the mirror is at 3cm (between the laser and prism out of the way of the original beam), the wall is at 15cm.
2. I’m pointing the laser dot through one side and using the internal reflection to project the dot through another prism face onto a wall.
3. I’m using the part of the light that reflects back from the prism and reflecting it into the dot on the wall using a mirror. The reflected beam is weaker than the one from the internal reflection, but it has good focus and decent intensity.
4. I’m observing the projected laser pattern when the two dots meet. I don’t have an expectation to see an unchanging cancellation or interference pattern, but I do expect to observe changes, fringe patterns, flickering or vibration in the projected dot when the two beam projections meet.
Reasons I don’t expect to see an unchanging pattern are:
A) I’m using a handheld mirror and my hands aren’t capable of statically holding a mirror to tens of nanometers :) That said, I should still be able to observe some kind of changes - flickering or optical artifacts.
B) One beam is slightly weaker (the one that reflects back). It may be tens of percent or many tens of percent less intense, but not by order(s) of magnitudes. Witnessing some sort of artifacts seems reasonable.
C) The beams are at a slight angle - one edge of the projection has had to travel longer. However seeing artifacts again should be a reasonable expectation.
Equipment:
i. Red laser pointer
The laser was purchased from http://www.amazon.com/gp/product/B0051223CU/?tag=pfamazon01-20. The pointer emits a red dot that (viewed very closely) seems to have a sparkling effect with lots of tiny-tiny dots. Its focus point is about 4mm, the focus at three meters is the same (or no more than 1-2mm larger), the focus at 25m is small as well - somewhere between the original 4mm and definitely not larger than a few cm. The label warns of eye exposure, declares compliance with 21 CFR and says the power is less than 1mW. The website says the wavelength is 650nm. It seems to be a genuine laser pointer. When doing the hair experiment and moving it in into the beam, I do see some sort of patterns indicative of interference.
ii. Glass prism
The glass prism is from http://www.amazon.com/gp/product/B00BNSU7FQ/?tag=pfamazon01-20. It reflects from the inner surfaces and reflects back to the original source.
iii. The mirror is http://www.amazon.com/gp/product/B003EB57MI/?tag=pfamazon01-20 (acrylic safety mirror). It’s not of the highest optical quality, but it does reflect well (the loss is less than from splitting the beam using the prism).
Attachments:
Images:
Setup:
1. I’m using a static laser pointer, a prism and a handheld mirror. The laser is at 0cm, the prism is at 7cm, the mirror is at 3cm (between the laser and prism out of the way of the original beam), the wall is at 15cm.
2. I’m pointing the laser dot through one side and using the internal reflection to project the dot through another prism face onto a wall.
3. I’m using the part of the light that reflects back from the prism and reflecting it into the dot on the wall using a mirror. The reflected beam is weaker than the one from the internal reflection, but it has good focus and decent intensity.
4. I’m observing the projected laser pattern when the two dots meet. I don’t have an expectation to see an unchanging cancellation or interference pattern, but I do expect to observe changes, fringe patterns, flickering or vibration in the projected dot when the two beam projections meet.
Reasons I don’t expect to see an unchanging pattern are:
A) I’m using a handheld mirror and my hands aren’t capable of statically holding a mirror to tens of nanometers :) That said, I should still be able to observe some kind of changes - flickering or optical artifacts.
B) One beam is slightly weaker (the one that reflects back). It may be tens of percent or many tens of percent less intense, but not by order(s) of magnitudes. Witnessing some sort of artifacts seems reasonable.
C) The beams are at a slight angle - one edge of the projection has had to travel longer. However seeing artifacts again should be a reasonable expectation.
Equipment:
i. Red laser pointer
The laser was purchased from http://www.amazon.com/gp/product/B0051223CU/?tag=pfamazon01-20. The pointer emits a red dot that (viewed very closely) seems to have a sparkling effect with lots of tiny-tiny dots. Its focus point is about 4mm, the focus at three meters is the same (or no more than 1-2mm larger), the focus at 25m is small as well - somewhere between the original 4mm and definitely not larger than a few cm. The label warns of eye exposure, declares compliance with 21 CFR and says the power is less than 1mW. The website says the wavelength is 650nm. It seems to be a genuine laser pointer. When doing the hair experiment and moving it in into the beam, I do see some sort of patterns indicative of interference.
ii. Glass prism
The glass prism is from http://www.amazon.com/gp/product/B00BNSU7FQ/?tag=pfamazon01-20. It reflects from the inner surfaces and reflects back to the original source.
iii. The mirror is http://www.amazon.com/gp/product/B003EB57MI/?tag=pfamazon01-20 (acrylic safety mirror). It’s not of the highest optical quality, but it does reflect well (the loss is less than from splitting the beam using the prism).
Attachments:
Images:
- labels on laser
- view into the pointy end of the laser, the diode lens being visible
- components
- focus point size at 3m
- experiment with me combining the beams and nothing happening
Attachments
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