2018 Nobel Prize in Laser Physics

When I arrived at Bell Labs in 1988 on a postdoctoral appointment to work with Alastair Glass in the Department of Optical materials, the office I shared with Don Olsen was next door to the mysterious office of Art Ashkin.  Art was a legend in the corridors in a place of many legends.  Bell Labs in the late 80’s, even after the famous divestiture of AT&T into the Baby Bells, was a place of mythic proportions.  At the Holmdel site in New Jersey, the home of the laser physics branch of Bell Labs, the lunch table was a who’s who of laser science.  Chuck Shank, Daniel Chemla, Wayne Knox, Linn Mollenauer.  A new idea would be floated at lunchtime, and the resulting Phys Rev Letter would be submitted within the month…that was the speed of research at Bell Labs.  If you needed expertise, or hit a snag in an experiment, the World’s expert on almost anything was just down a hallway to help solve it.

Bell Labs in the late 80’s, even after the famous divestiture of AT&T into the Baby Bells, was a place of mythic proportions.

One of the key differences I have noted about the Bell Labs at that time, that set it apart from any other research organization I have experienced, whether at national labs like Lawrence Berkeley Laboratory, or at universities, was the genuine awe in people’s voices as they spoke about the work of their colleagues.  This was the tone as people talked about Steven Chu, recently departed from Bell Labs for Stanford, and especially Art Ashkin.

Art Ashkin had been at Bell Labs for nearly 40 years when I arrived.  He was a man of many talents, delving into topics as diverse as the photorefractive effect (which I had been hired to pursue in new directions), nonlinear optics in fibers (one of the chief interests of Holmdel in those days of exponential growth of fiber telecom) and second harmonic generation.  But his main scientific impact had been in the field of optical trapping.

Optical trapping uses focused laser fields to generate minute forces on minute targets.  If multiple lasers are directed in opposing directions, a small optical trap is formed.  This could be applied to atoms, which was used by Chu for atom trapping and cooling, and even to small particles like individual biological cells.  In this context, the trapping phenomenon was known as “optical tweezers”, because by moving the laser beams, the small targets could be moved about just as if they were being held by small tweezers.

In the late 80’s Steven Chu was on the rise as one of the leaders in the field of optical physics, receiving many prestigious awards for his applications of optical traps, while many felt that Art was being passed over.  This feeling intensified when Chu received the Nobel Prize in 1997 for optical trapping (shared with Cohen-Tannoudji and Phillips) but Art did not.  Several Nobel Prizes in laser physics later, and most felt that Art’s chances were over … until this morning, Oct. 2, 2018, when it was announced that Art, now age 96, was finally receiving the Nobel Prize.

Around the same time that Art and Steve were developing optical traps at Bell Labs using optical gradients to generate forces on atoms and particles, Gerard Mourou and Donna Strickland in the optics department at the University of Rochester discovered that optical gradients in nonlinear crystals could trap focused beams of light inside a laser cavity, causing a stable pulsing effect called Kerr-lens modelocking.  The optical pulses in lasers like the Ti:Sapphire laser had ultrafast durations around 100 femtoseconds with extremely stable repetition rates.  These pulse trains were the time-domain equivalent of optical combs in the frequency domain (for which Hall and Hansch  received the Nobel Prize for physics in 2005).  Before Kerr-lens modelocking, it took great skill with very nasty dye lasers to get femtosecond pulses in a laboratory.  But by the early 90’s, anyone who wanted femtosecond pulses could get them easily just by buying a femtosecond modelocked laser kit from Mourou’s company, Clark-MXR.  These types of lasers moved into ophthalmology and laser eye surgery, becoming one of the most common and most valuable commercial lasers.

Donna Strickland and Gerard Mourou shared the 2018 Nobel Prize with Art Ashkin on laser trapping, complementing the trapping of material particles by light gradients with the trapping of light beams themselves.