A friend of mine is a researcher in the field of chemical physics. This week, he invited me to his lab to take a photograph of his 5 megawatt laser, which strikes a copper target and makes a plume of plasma that lasts for just a few fleeting nanoseconds. Normally, I like taking photos of landscapes or architecture, but there’s no way a geek like me can resist the invitation to play with a frickin’ laser.
Naturally such a powerful laser is potentially rather dangerous, so I was under strict instructions not to touch anything, lest I get my hand zapped off or something. Laser safety goggles were the order of the day. As they say, “do not stare into beam with remaining eye.”
The laser table is large and complex. The laser itself is on the far side of the table, behind the computer screen. The beam then bounces around various mirrors and lenses in the section of the table on the left, which has black safety screens to catch any stray reflections. I am told that if any dust gets on the mirrors, it will absorb enough laser energy to become hot enough to damage the mirror.
The beam then enters the metal tube at the front of the table, and finally zaps the copper target in the square metal box in the near-left corner. The box contains a near-vacuum, with a pressure of just 3 ten-billionths of normal atmospheric pressure. The box has an observation window, and if you look carefully you can see my black camera over the hole, peering through the window.
The white box in the very foreground is a specialised laser detector, fitted out with all sorts of gizmos, including the computer on the trolley.
Finally, the image we’ve been waiting for. This picture shows the inside of the box. The green laser beam enters the picture from the right, but you can’t see it because there is no mist or smoke for it to reflect from. The centre of the bright flash is where the beam strikes the copper, and you can see a bit of green in there. The plume of plasma then spreads back along the beam, heading right. It isn’t also going left – what you can see there is a reflection of the plume on the shiny copper surface. Not sure what else I can say about this. I’m no expert! 
Jonathan Gazeley 
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