Photonics paves the way for a Nobel Prize
Three laser scientists share the 2018 Nobel Prize for Physics. The prize winners in Chemistry and Medicine also used photonic technologies in their research.
With Arthur Ashkin, the connection to photonics is obvious. Back in the 1960s, the experimental physicist, who was born in 1922, carried out the first experiments in the Bell Laboratories to move small particles with the help of radiation pressure. His first publication on the subject, Acceleration and trapping of particles by radiation pressure, in 1970 presented the prospect of optical tweezers, for which he was now awarded the Nobel Prize. In the beginning, Ashkin experimented with dielectric particles, which he was able to move in air and water with the help of two opposing laser beams. Several intermediate steps followed, including a vertical laser where particles were suspended in the beam at the point where the radiation pressure and gravitational force balanced each other. In 1986, his team succeeded in developing a single-beam gradient force optical trap, which is considered to be the first optical tweezers. But his scientific curiosity was by no means satisfied. His goal: using lasers to make living cells and viruses tangible without destroying them, which he achieved by changing from green to infrared wavelengths. These days, biological research would be almost inconceivable without optical tweezers. They fix proteins, molecular motors, DNA, and give scientists deep insights into living cells.
High energy, ultrashort laser pulses
The other half of the 2018 Nobel Prize for Physics is shared by Donna Strickland from Canada and Gérard Mourou from France for the development of chirped pulse amplification (CPA)—a method to generate extremely short, intensive laser pulses. To put it simply: in chirping, ultra-short pulses are stretched with the aid of optical lattices, mirrors, or prisms. This reduces their peak powers and, consequently, the stress on the material in the subsequent amplification in the laser medium. The amplified pulses pass through another optical device that compresses them again. With this optical compression the pulse intensity increases considerably. Since the two scientists made the breakthrough in 1985, their process has become very popular—and is gaining ground in industrial material machining processes as well as in physical, chemical, and medical applications—in both research and clinical practice. Laser scientists are driving pulse durations into new realms, from femto (10-15) to atto (10-18), to zeptoseconds (10-21). The powers are also increasing to the petawatt range. A PW laser pulse corresponds to the entire thermal output that the Gulf Stream transports.
Endogenous immune defense fights cancer
James P. Allison and Tasuku Honjo independently identified proteins that slow down and speed up the T cells that are key for our immune defense. Allison took a close look at CTLA-4, which he could switch off with an antibody developed especially for this purpose. His idea was that, if he could release the CTLA-4 brake of the T cells, the body’s own immune defense could attack malignant tumors. The first experiments showed a disruptive effect. Honjo even succeeded in healing patients with metastasized cancer in their body with the brake protein PD-1. Although it sounds simple when described in just a few sentences, it is the result of many years of research with different analytic approaches. In addition to microscopic examinations of tissue, in some cases using fluorescent dyes, immune therapy research is increasingly focused on flow cytometry in an FACS (fluorescence activated cell sorter). In this method, fluorescent molecules are anchored to cells, which are then gradually excited with lasers with different wavelengths. The devices can analyze more than 1000 cells per second. The emitted light provides an indication of the cell population in the samples. Antibody detection methods, such as ELISA (enzyme-linked immunosorbent assay) and ELISpot (enzyme-linked immunospot assay) are also based on photometry, luminescence analyses, and camera-based evaluations; in other words, they use photonics technologies.
The 2018 Nobel Prize for Chemistry was shared by biochemist Frances H. Arnold for her re-search into directed evolution of enzymes and George P. Smith and Sir Gregory P. Winter for their contribution towards the development of the phage display to create monoclonal antibodies on a purely human basis. The instruments of the scientists include various spectroscopic processes and fluorescence-based polymerase chain reaction (PCR) to specifically amplify DNA with mutations. In other words, photonics, which has been enabling top-class cross-disciplinary research for many years.