Researchers set a new record for the strongest ultra-short laser pulses

Lasers are devices that excite atoms and molecules in a material to radiate light of a specific wavelength through a mechanical process of stimulated emission. Lasers that generate concentrated and continuous light beams are quite common.

However, in rare circumstances, researchers or industries might require very short and strong pulses of laser light. Such laser beams can be used for precise cutting or laser ablation.

A team of researchers at ETH Zurich has achieved a new record of producing the strongest ultra-short laser pulses. These laser pulses could be used for meticulous measurements and materials processing.

Professor Ursula Keller at the Institute for Quantum Electronics led the team to produce 550 watts of power, i.e., energy of 100 µJ, which surpasses the previous maximum by 50%.

These are the highest average power and highest pulse energy ever generated by a laser oscillator. These pulses last for an extremely short duration (less than a picosecond) and exit the laser in a regular sequence at a high rate of five million pulses per second.

Researchers discovered novel way of generating ultra-short bursts of light

Researchers claim that the pulses can reach the power of 100 megawatts, which in theory is sufficient enough to power one lakh vacuum cleaners.

Ursula Keller believes that this new laser could have potential applications in ultraviolet X-ray regimes, leading even precise clocks.

The research group has been working on advancements in the short pulsed disk lasers (100 micrometers thick) for the last 25 years. During this time, the group encountered several challenges in further elevating the power, followed by a few devastating incidents.

“This record is the result of a long and exciting journey with lots of interesting laser physics,” says Ursula Keller.

The recording breaking power and pulse rates are based on two innovations. First, a special mirror arrangement sends the light inside the laser and reflects several times before it leaves the laser through an outcoupling mirror. This configuration enabled the researchers to amplify the light without becoming unstable.

Meanwhile, the second innovation is the use of SESAM (Semiconductor Saturable Absorber Mirror), invented by the group leader Keller. SESAM’s reflectivity depends on the intensity of the light striking it.

Using the SESAM, researchers were able to redirect short pulses rather than a continuous beam. The pulses have extremely high intensity as the light energy is concentrated during a short period.

Up to now, pulses with power could only be generated by sending weaker laser pulses through several separate amplifiers. However, such amplifications produced loud noise. Therefore, scientists attached a semiconductor layer of the SESAM mirror to a thin sapphire window and generated the high power directly using the laser oscillator.

“The support by ETH Zurich over the years and the reliable funding of my research by the Swiss National Fund have helped me and my collaborators reach this great outcome. We now also expect to be able to shorten these pulses very efficiently to the regime of a few cycles, which is very important for creating attosecond pulses,” says Keller

Quantum squeeze to make clocks more precise

“A dream would be to show, one day, that the natural constants aren’t constant after all. All in all, one can say that with our pulses lasers, we have shown that laser oscillators are a good alternative to amplifier-based laser systems and that they enable new and better measurement,” Keller continued.

Journal Reference