Fun With A 200-kW Fiber Laser

We’ve all heard the “Do not stare into laser with remaining eye” joke. It’s funny because it’s true, as pretty much any laser a hobbyist can easily come by can cause permanent damage to eyes unless the proper precautions are taken. But a fiber laser with 200kW peak power is in another hazard class entirely.

Granted, outsized power ratings like this are a bit misleading, based as they are on femtosecond-long pulses. And to be sure, the fiber laser that [Marco Reps] tears down in the video below was as harmless as a kitten when he got it, thanks to its output optics having been unceremoniously shorn from the amplifier by its former owner. Reattaching the output and splicing the fiber would be necessary to get the laser lasing again, but [Marco] had other priorities in mind. He wanted to understand the operation of a fiber laser, but the tangle of fibers on two separate levels inside the chassis was somewhat inscrutable. The coils of fiber wrapped around the aluminum drums inside the chassis turned out to be the amplifier; fed by a semiconductor seed laser, the light pulse travels through the ytterbium-doped fiber of the two-stage amplifier, which is the active gain medium where stimulated emission, and therefore amplification, occurs.

With a little reverse engineering and the help of an online manual, he was able to understand the laser’s operation. A laser company helped him splice the optics back together – seeing the splicing rig in action is worth the price of admission alone – and the unit seems to be in more or less working order at this point. Normally the most powerful laser we see around here are the CO2 lasers in those cheap Chinese laser cutters, so we’re looking forward to learning more about fiber lasers.

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First Light: The Story Of The Laser

Lasers are such a fundamental piece of technology today that we hardly notice them. So cheap that they can be given away as toys and so versatile that they make everything from DVD players to corneal surgery a reality, lasers are one of the building blocks of the modern world. Yet lasers were once the exclusive province of physicists, laboring over expansive and expensive experimental setups that seemed more the stuff of science fiction than workhouse tool of communications and so many other fields. The laser has been wildly successful, and the story of its development is an intriguing tale of observation, perseverance, and the importance of keeping good notes.

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How Lasers Actually Work

Lasers are optical amplifiers, optical oscillators, and in a way, the most sophisticated light source ever invented. Not only are lasers extremely useful, but they are also champions of magnitude: While different laser types cover the electromagnetic spectrum from radiation (<10 nm) over the visible spectrum to far infrared light (699 μm), their individual output band can be as narrow as a few µHz. Their high temporal and spatial coherence lets them cover hundreds of meters in a tight beam of lowest divergence as a perfectly sinusoidal, electromagnetic wave. Some lasers reach peak power outputs of several exawatts, while their beams can be focused down to the smallest spot sizes in the hundreds and even tens of nanometers. Laser is the acronym for Light Amplification by Stimulated Emission Of Radiation, which suggests that it makes use of a phenomenon called stimulated emission, but well, how exactly do they do that? It’s time to look the laser in the eye (Disclaimer: don’t!).

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