The Imperial Festival ran from 12 - 6pm today at the South Kensington Campus of Imperial College, I was lucky enough to have been able to show the public the extra cool side of lasers.
Team Laser, including myself and the amazing Tim Robinson, a PhD student of the Plasma Physics Department hosted the stand. We showed the visitors at the Festival how lasers can be totally internally reflected in a fish tank full of sugar and water; how Newton's rings (an interference phenomena that shows the wave nature of light) can form on your phone screen; how lenses can be used to converge and diverge light and the grande finale was using a Class 3B laser to pop a balloon! The balloon popping laser gained a lot of love from the public, particularly the young ones where there were many screams and jumps due to the unexpected nature of the pop!
But what made my day was not only having fun with lasers but being able to act as a female role model for the many young females that visited my stand - I was asked about my education path so far and it was nice to share my story and (hopefully) inspire some of them.
Before some pictures, let me tell you more about the science of the experiments at my stand. The first experiment was showing total internal reflection with a laser in a fish tank with water and sugar. You can do this at home - all you need is a laser pointer, a cup/clear container and sugar. Mix the sugar and water in a 1:1 ratio and then just shine the laser into the container. The sugar molecules act as a 'scatterer' and scatter the light from the laser allowing you to see the laser beam. If the laser is titled in such a direction, the laser beam can be contained within the liquid - this is called total internal reflection and can be seen in the following image.
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| Total internal reflection |
Total internal reflection occurs at a certain angle known as the critical angle at the boundary between two different media. This phenomena is used in fiber optics to convey information over long distances with minimum loss.
The next experiment at my stand was simple use of two laser pointers parallel to each other and when passed through a converging or diverging lens you can see the two dots from the laser beam come closer or further apart from each other.
The third experiment was producing Newton's rings, an interference effect when two pieces of glass are placed on top of each other, like this:
This was the laser pointer I used and I added some tape on the end which dispersed the light (it wasn't clear tape, it looked 'milky'):
As you can see above, the laser pointer was pointed directly downwards onto the glass and an interference pattern was viewed on the tape. An interference pattern consists of dark and bright bands, where the dark bands show destructive interference (light waves cancel each other out) and the bright bands show constructive interference (where the light waves add together just like a water wave to produce a bigger wave, and in the case of the light, a brighter wave). This could also be done with a phone screen!
The pop-o-matic, a balloon-popping laser, is a class 3B laser, meaning that they are hazardous for eye exposure and can heat skin/materials but are not considered a burn hazard. There is a converging lens in the chamber of the pop=o-matic which focuses the light to a small point. Intensity is equal to the power per unit area which means if there is a small area there is a larger intensity for a given power - thus, the focused laser beam has a high intensity. Power is proportional to energy and so intensity is proportional to energy, therefore the focused laser beam has a high energy in a small area, this burns through the balloon and pops it! If the laser beam is green and we place a green balloon in the beam it doesn't pop because green object reflect green light and so the laser light is reflected by the balloon and the energy does not go into the balloon and does not pop. So this is a great demonstration for showing the relationship between intensity, power, energy and area and also how we see colour.
The next experiment at my stand was simple use of two laser pointers parallel to each other and when passed through a converging or diverging lens you can see the two dots from the laser beam come closer or further apart from each other.
The third experiment was producing Newton's rings, an interference effect when two pieces of glass are placed on top of each other, like this:
As you can see above, the laser pointer was pointed directly downwards onto the glass and an interference pattern was viewed on the tape. An interference pattern consists of dark and bright bands, where the dark bands show destructive interference (light waves cancel each other out) and the bright bands show constructive interference (where the light waves add together just like a water wave to produce a bigger wave, and in the case of the light, a brighter wave). This could also be done with a phone screen!
The pop-o-matic, a balloon-popping laser, is a class 3B laser, meaning that they are hazardous for eye exposure and can heat skin/materials but are not considered a burn hazard. There is a converging lens in the chamber of the pop=o-matic which focuses the light to a small point. Intensity is equal to the power per unit area which means if there is a small area there is a larger intensity for a given power - thus, the focused laser beam has a high intensity. Power is proportional to energy and so intensity is proportional to energy, therefore the focused laser beam has a high energy in a small area, this burns through the balloon and pops it! If the laser beam is green and we place a green balloon in the beam it doesn't pop because green object reflect green light and so the laser light is reflected by the balloon and the energy does not go into the balloon and does not pop. So this is a great demonstration for showing the relationship between intensity, power, energy and area and also how we see colour.
Here are some more images for you to enjoy!
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| Green class 3B laser, courtesy of Professor Roland Smith of the Plasma Physics Department, Imperial College |
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| Popping red coloured balloons with a laser! |
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| Tim working his magic with the pop-o-matic and sharing knowledge about the way we see colour |
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| Red and green lasers in a fish tank with water and sugar |
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| Light writing |
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| Plastic Electronics |
The Imperial Festival runs tomorrow from 12 - 5pm and you can enjoy all these laser activities and more! Hope to see you there!
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