IELTS Preparation Series 2, Episode 6: Lasers
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Hello. I'm
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Margot Politis. Welcome to Study English, IELTS preparation.
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Today we're going to learn about lasers - what are they, and how they work.
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We'll also practice structuring a description of how something works, and we'll work on
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our vocabulary for describing colours.
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Let's begin by listening to Imogen Jubb talk about the history and the science of lasers.
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Lasers are used in all sorts of settings like welding,
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cutting,
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surgery,
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communications,
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reading bar codes at the supermarket
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or reading the information stored on a CD or DVD.
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There are many types of lasers but they all have 3 main parts to them. They all have an
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energy source, such as a lamp, some sort of feedback mechanism, like this pair of mirrors,
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and also some medium, like the ruby crystal, which can amplify the light.
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Now the first laser was built in the 1960s. It was made from a ruby crystal, some lamps
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and 2 mirrors, one on either side of the crystal.
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I've got a sort of model of it here.
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The lamp shines white light onto the crystal, which is represented by this tube. Pumping
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energy into the crystal actually gives off light at a particular frequency to produce
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a particular colour.
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Some of this light bounces backwards and forwards between the two mirrors, and passes through
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the crystal each time.
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Each time the light goes through the crystal, it gets amplified, stimulating the same energy
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release in other parts of the crystal. So after many times in between the two mirrors,
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and many reflections passing through the crystal, you end up with a very strong, narrow beam
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of light that is just one colour.
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One of the mirrors is only partially reflective, so some light passes out as the laser beam.
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Before Imogen explains the laser to us, she starts with an 'introduction', or 'orientation'.
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That way, we know what to focus on.
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If you're describing a device or a tool, it's a good idea to introduce it by naming it and
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describing what it's used for.
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This is useful in spoken English, and it's also a good way to begin if you are writing
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in formal English.
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Listen to how Imogen introduces the laser.
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Lasers are used in all sorts of settings like welding,
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cutting,
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surgery,
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communications,
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reading bar codes at the supermarket
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or reading the information stored on a CD or DVD.
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She talks about the function of the laser and lists a few of the things we use lasers
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for today.
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In formal writing, if you were to introduce a discussion of lasers, you could structure
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your opening paragraph in a few ways.
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One idea would be to start like this:
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A laser is a device designed to intensify a beam of light.