What is Ultrashort Pulse Laser Technology? Applications of Ultra-Short Laser Pulses

The idea of an ultrashort pulse is one of the most interesting and developed new concepts in femtotechnology today. Generally, when we say “ultra-short pulse”, we’re talking about ultrashort pulse laser technology, but this term can encompass any area of the electromagnetic spectrum- and indeed, it’s conceivable that there could be an ultra-short pulse of air, water, or other chemicals as well. However, ultra-short pulse lasers are of the most value to science right now, and this is one area where femtoscience is already making waves. You very likely have something in your pocket right now that’s been created with the help of ultrashort laser pulses- we’ll get to that later.

An ultrashort pulse is created by a special sort of laser emitter- a mode-locked oscillator. Mode locking involves allowing a laser to pass between mirrors for a very short amount of time, which makes the already-synchronized waves of light even more synced up.

Getting Energized With Chirped Pulse Amplification

While the creation of one of these ultrafast events is difficult enough, the challenge for a long time was the strength of the laser. If you shine a laser for a short amount of time and it’s next to powerless, there’s no benefit; the importance of this technology is also dependent on the power output.

Getting an amplified level of power requires a special cutting-edge technique known as chirped pulse amplification– where a short, weak pulse is generated, then stretched out through a grating, then amplified, recompressed with a reverse grating, and sent out, maintaining its amplified power. This is one of the only methods that doesn’t overload the machinery during the powerful amplification process.

Chirped Pulse Amplification for an Ultrashort Laser Pulse

A diagram of chirped pulse amplification, needed to produce an ultrashort laser pulse. Image by US Energy Department.

These pulses have opened up a new subfield of chemistry, brought about new procedures in optics, revolutionized areas of manufacturing, and more. But just how small is an ultrashort laser pulse?

Ultrashort Pulse Lasers- How Short is Ultrashort?

“Ultrashort” is, in this scientific context, the magnitude of a picosecond– that’s 10-12 seconds. Ultra-short can mean pulses even less than that, too.

How does this relate to minutes, to hours, to years, and more? One picosecond is…

  • 1.0 x 10-12 seconds
  • 1.7 x 10-14 minutes
  • 2.8 x 10-16 hours
  • 1.2 x 10-17 days
  • 3.2 x 10-20 years
  • 3.2 x 10-21 decades
  • 3.2 x 10-22 centuries
  • 3.2 x 10-23 millenia

Or in reverse:

  • One second is 1,000,000,000,000 (one trillion) picoseconds
  • One minute is 6.0 x 1013 picoseconds
  • One hour is 3.6 x 1015 picoseconds
  • One day is 8.6 x 1016 picoseconds
  • One year is 3.2 x 1019 picoseconds
  • One decade is 3.2 x 1020 picoseconds
  • One century is 3.2 x 1021 picoseconds
  • One millenium is 3.2 x 1022 picoseconds
  • And, for the finale, the age of the Universe is 4.3 x 1029 picoseconds.

In a picosecond, light in a vacuum travels 0.0118 inches or 0.2998 millimeters.

With such huge/tiny numbers at play, these conversions can be a little hard to grasp mentally. Turns out, there are now even shorter pulses possible, on the realm of the attosecond. As a comparison, the Universe is 4.3 x 1035 attoseconds old.

The Field of, and the Father of, Femtochemistry

The Father of Femtochemistry: Ahmed Hassan Zewail

The Father of Femtochemistry: Scientist Ahmed Hassan Zewail (source)

The first Egyptian scientist to ever win a Nobel Prize in a science-related field is named Ahmed Hassan Zewail, born in 1946. He’s a prominent and highly-regarded chair professor at the California Institute of Technology, as well as the director of the Physical Biology Centre for the Ultrafast Science and Technology. He is also known as the Father of Femtochemistry.

Dr. Zewail’s biggest contribution to science is his remarkable methods of analyzing chemical reactions at the femtosecond level. Using ultra-short laser flashes, he invented/discovered/created a technique to observe and describe these chemical reactions at time intervals so short, the very transition states of matter can be peered into.

In particular, one experiment with a molecule of anthracene (a grey, sandy substance consisting of three Benzene rings joined together) provided some surprising results. The molecule was thought to decay rather chaotically, but at these tiny time intervals, an order emerged from this chaos, and Dr. Zewail and his team observed coherence in atomic motion.

This level of observation opened up the entire field of femtochemistry, which is extremely interesting in it’s own right- all thanks to a new use of ultrashort pulses. Ultrashort pulse laser technology was also responsible for the creation of femtobiology. Dr. Zewail moved on to even smaller intervals of time, and has now won so many awards and honors thanks to his work it’s hard to even list them all. It’s worth noting that he’s a prominent Muslim scientist and has acted as an envoy and educator to many countries around the world, too. Dr. Zewail- Femtotechnology News salutes you!

Applications in Optics, Manufacturing, and More

Lasers are amazingly effective tools in a vast number of fields. We use lasers everywhere from medical operations– in eye surgery (you’ve no doubt heard of Lasik)- to manufacturing plants in high-powered laser cutters. However, lasers get hot. Shine a laser against a piece of metal- or the surface of someone’s eye- for more than a few moments, and the surface area starts heating up. When that happens, metal melts, surfaces become irregular, and flaws introduce themselves into whatever you happen to be working with. When we talk about laser precision cutting, we demand that the precision come not at the cost of the coherence of our work! Luckily, the ultrashort pulse laser overcomes these difficulties.

Since the laser is so fast, the surface doesn’t even have time to heat before the work is already done. Controlled by highly accurate computers down to these fractions of fractions of seconds, the target of the laser is vaporized before your reaction time tells you it’s even begun. This is called cold ablation, and it’s so powerful that inscriptions can be engraved (or, really, ablated) onto the head of a match without setting it on fire. One of the biggest challenges, though, was converting this from a specifically-configured advanced laboratory tool, into a machine that could be used on the manufacturing floor that could be reasonably invested in by businesses in need. After all, practical applications of femtotechnology are not practical if they’re too expensive and specialized for anyone to afford or require.

German scientists Jens König, Stefan Nolte, and Dirk Sutter, working for technology company Bosch (the source of the above video as well as the top image in this article), were able to make this conversion. For this they were awarded the German Future Prize 2013. Now, cold ablation techniques are being used in more and more manufacturing plants across the world. USP has the added benefit of being effective on essentially any substance– even materials that are difficult or impossible to cut and etch traditionally, such as diamond, crystal, ceramic, semiconductor bases, sensitive plastics, and the surface of eyes. In fact, ultrashort pulse lasers were likely used during the crafting of the delicate touch-screen on your smartphone. Femtotechnology isn’t so far off in the future after all!

Conclusion

Ultrashort pulse lasers are already revolutionizing areas of chemistry, manufacturing, healthcare, and more. We’ve seen how they give us a new light on the intricacies of chemical reactions; we’ve also seen how laser pulse cold ablation puts production plants on the cutting edge. All thanks to many dedicated scientists who have put in long hours of hard work and intense research, so all of humanity can benefit from our increased understanding and mastery over the physical world around us.

Have we missed anything? Let us know in the comments below!

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Written by Ethan J. Hulbert

Ethan J. Hulbert is a scientist and marketing professional from Chicago, IL. Find out more about Ethan at ethanjhulbert.org.