New Femtosecond Laser Reported by Scientists

A team of scientists based in Poland reports a new femtosecond laser - with the latest light source potentially game-changing for various applications.

Laser sources are often constructed specially to meet specialized applications - from observing objects in outer space, treating illnesses in the human body to fabricating materials in the micro and nanoscales.

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A New Class of Laser

"Our goal is to develop new ones," says Yuriy Stepanenko, leader of the study and team head at the Ultrafast Laser Techniques at the Polish Academy of Sciences' Institute of Physical Chemistry, in a statement. He further explains that they deal with sources capable of delivering "ultrashort pulses of light," or those in the femtosecond pulses. A femtosecond is equivalent to one to the negative fifteenth (10-15), or one-part in a quadrillion, of a second. Stepanenko adds that this is the scale at which intracellular chemical reactions occur, and to "see" these events, they have to take a photo in that extremely short period of time - and the new laser can do just that.

The Polish scientist also adds that the femtosecond laser can also be used for the "very precise removal" of foreign materials on surfaces without harming or even destroying them. For example, the famous painting Mona Lisa can supposedly be cleaned without damaging the layers of paint on the artwork. The femtosecond laser would only remove dust and dirt that is a layer about 10 nanometers thick, according to Stepanenko.

Dr. Bernard Piechal, a co-author of the study, adds that the laser might even be "too precise" for the artwork application, saying that the task only requires lasers in the nanosecond scale. As for the new laser, Piechal explains that it can be used for engraving precise paths in ultrathin materials, such as scraping gold off microchips with precise depth measurement. Using a nanosecond laser for such applications could melt the silicon in the chip or break the glass with its longer exposure time.

Their findings are published in the Journal of Lightwave Technology.

Creating Harmonics in Light Pulses

Piechal explains that they aimed for a laser source that could meet two conditions. The first is that the source has to be "susceptible to mechanical disturbance to the least possible extent," and the second is that the source has to be mobile. It led the researchers to fiber-optic lasers, which, according to Stepanenko, is "basically an optical fiber enclosed in a ring." The light inside these fibers is greatly protected from mechanical disturbances, consistently transmitting light pulses even when moved or physically touched.

The other challenge is the frequency of light pulses emitted. Conventionally, the frequency is affected by the length of the fiber optic loop where the light pulse passes through, and higher frequencies would require longer cables, which was not ideal for the researchers. They then reduced the circumference of the loop. But still, the pulses achieved was around 60 nanoseconds. To work around this limitation, researchers designed a system that can duplicate the frequency to achieve a higher output, similar to creating harmonic frequencies, in a tech known as Harmonic Mode Locking.

Stepanenko compares the tech to a guitar, where the basic frequency is an open string. They can then choose which harmonics they will use, similar to achieving a higher note on a guitar string by pressing on the middle of the fretboard.