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A complete idiot's laser question


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Sounds like you need a basic in wavelengths and light!


Here is the main parts of the EM (electromagnetic) spectrum:


Radio waves | Micro waves | infrared | visible light | ultra violet | x rays | gamma rays


Left = low frequency, high wavelength

Right = high frequency, low wavelength


Frequency and wavelength are inversely proportional, meaning as one increases the other decreases. The speed of the wave is

wave speed = wavelength x frequency

and as the wave speed for EM waves is a constant (c - the speed of light) you can easily see that if the wavelength increases the frequency must decrease.


With lasers it's all about the power, not so much the wavelength (and consequently the frequency).


Classically red lasers are used in 'laser cutters' because red lasers are popular and most common because they are easiest to produce. Recently different frequency lasers are becoming more and more common... OK, they've been around for a while, but who had heard of a green laser in the 90s? (other than a few involved in that kind of work, or possibly a hobbyist)


Now you can get green laser pens for about £30 (UKP) which is roughly $70 (USD).


I'm kinda sidetracking... back on topic... it's all about the power. Look on e-bay, all the green lasers have a power limit of 5mW, if you look around a lot there will be a few saying that they will 'unofficially' give you an upgrade.


I can't find the website but it showed pictures of a 25mW laser, a 50mW, a 100mW and a 200mW and the difference was quite vast. Also I found a random website which was selling a 200mW green laser, it had warnings that it was far too bright to look at with the bare eye.


Also you will see class II or class IIIA or something, the class is referring to it's power.


Basically it boils down to the power rating of the laser more than the colour (different colours are different frequency (and consequently different wavelengths)).

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I do know the short-wave-length beams are able to read much greater amounts of information across smaller spaces. But I'm talking major-lab quality mega-beams


Oh, maybe my last post wasn't soo much what you were looking for.


Basically lasers with a smaller wavelength can fit inside smaller spaces so can read CDs more finely. Think of it this way, a fat laser can read a certain amount of bits on a CD, but a smaller thinner laser can read data several times over in the same space that a single fatter laser can fit once.


The new blue-ray discs that are coming out before 2010 (I think) use a blue laser because of the smaller wavelength, it can fit far more data per CD, it's a revolution.... except that an even better CD is coming out soon after that due to a breakthrough in CD data encryption a while back whereby they can encrypt several bits per 'trough' in the CD.


Smaller wavelengths are more fine and can also travel further, although that is not a feature in CD players, a green laser can travel vastly further than a red laser, I think it was between 5 and 10 times as far, and also you can see the beam in the air because, think of it this way: the smaller wavelength means it can bounce off atoms which a laser with a bigger wavelength would just go over.

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With lasers it's all about the power' date=' not so much the wavelength (and consequently the frequency).


Classically red lasers are used in 'laser cutters' because red lasers are popular and most common because they are easiest to produce. [/quote']


There's some physics behind this. Usually to get a laser working you need a population inverson, which means more atoms in an excited stated than in some state below it. But lifetime varies as 1/frequency3 so in shorter wavelength lasers it's harder to get an inversion - the spontaneous decay gets large. It's for this reason that the first amplification system was done with very small frequencies - microwaves. Masers came before lasers.


"all about the power" may be true for cutting, but not for all applications. Many require specific wavelengths so that you can be on resonance with a specific atomic or molecular transition. This also may require tunability - a lot of the early lasers were not tunable. The diode laser really revolutionized laser applications in spectroscopy and related fields. In those cases IR was easy to do with material like GaAs and AlGaAs, but getting to shorter wavelengths through the visible required more and more complicated fabrication techniques to get a larger bandgap in the semiconductors used.

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Alright, just a clarification question. The colour of the laser signifies it's strength?


YT is absolutely correct.


The color tells you it's wavelength and frequency, which are related. [math]\lambda\nu = c[/math]. Power is measured in Watts, and that tells you how much energy per unit time the laser sends out. You'll see some lasers advertised as being brighter than others. But that's because your eye is most sensitive to green light, near 550 nm, so a "bright" laser is not necessarily more powerful - your eye can be 10-100 x more sensitive to green that to red and blue light (depending on where you are in the red or the blue). The danger is that a laser in the near IR or UV can harm you before you can realize it, since the light doesn't seem bright

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