Re: Green laser pointers (fwd)

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Original poster: Steven Roys <sroys@xxxxxxxxxx>



---------- Forwarded message ----------
Date: Sun, 01 Jul 2007 22:22:41 -0400
From: David Speck <dave@xxxxxxxxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Re: Green laser pointers (fwd)

Pete,

Lasers work when electrons fall from an energized orbital state to a 
lower energy state.  The change in energy determines the energy of the 
radiated photon, and, as Mike indicated, the color, according to the 
frequency of the radiated photon.

The particular energy levels involved are characteristic of the excited 
element in the laser.  There are a finite number of elements or exotic 
compounds to start with, and only select subset of those have suitable 
chemical, mechanical, optical and photoelectric properties suitable for 
laser construction. 

As I understand it (and I may be wrong or incomplete), the green lasers 
start with a high powered invisible infrared laser source which passes 
through a frequency doubling crystal.  The doubling crystal has the very 
unusual property of absorbing light at a low frequency and reemitting it 
at double the frequency, or half the wavelength, of the incoming light.  
This is contrary to the common property of many phosphors which absorb 
light of one wavelength and then re-radiate it at a longer (lower 
frequency) wavelength, while dissipating the difference in energy as heat. 

It just happens that the properties of current gallium indium arsenide 
(or whatever is the current highest power laser chips are made of) make 
them extremely efficient at emitting infrared light at about 1000 nm, 
which, when doubled in frequency, turns out to be green light at about 
500 nm wavelength.  If the exciting wavelength were longer, and the 
doubling crystal still happens to work efficiently at that wavelength, 
then you could theoretically get yellow, orange, or red light out of a 
DPSS laser. 

Dave
>   Steve, or anyone else...,
>
> I've always wondered why they can make such hi-powered green
> lasers, but not red or yellow ?
>
> -Pete Lawrence.