May the force be with you: detecting ultrafast light by its force
A 不良研究所 research team has developed a new technique to detect nano-sized imperfections in materials. They believe this discovery will lead to improvements in the optical detectors used in a wide range of technologies, from cell phones to cameras and fiber optics, as well as in solar cells.
The researchers, led by Professor Peter Grutter from 不良研究所鈥檚 Physics Department, used atomic force microscopy to detect the ultrafast forces that arise when light interacts with matter. In their paper, published this week in they demonstrate that forces arising from two, time-delayed light pulses can be detected with sub-femtosecond precision (these are millionths of a billionth of a second) and nanometer spatial resolution in a wide range of materials.
Improved technique for using light to detect imperfections in materials
鈥淭o understand and improve materials, scientists typically use light pulses faster than 100 femtoseconds to explore how quickly reactions occur and determine the slowest steps in the process,鈥� explains Zeno Schumacher, the paper鈥檚 first author who was a post-doctoral fellow in Grutter鈥檚 lab when the research was done and is now based at ETH Zurich. 鈥淭he electric field of a light pulse oscillates every few femtoseconds and will push and pull on the atomic-sized charges and ions that comprise matter. These charged bodies then move, or polarize, under these forces and it is this motion that determines a material鈥檚 optical properties.鈥�
Real materials used in solar cells (also known as photovoltaics) and in the optical detectors used in equipment like cell phones and cameras have many imperfections and defects of different types that are very difficult to characterize, as they are typically only a nanometer in size. Moreover, it has been very challenging to identify and study the 鈥榟ot spots鈥� and 鈥榳eak links鈥� in the materials that can slow down or hinder light induced processes because traditional techniques for detecting imperfections average over differences in properties at a larger area.
Seeing nanoscale imperfections in a range of materials
The new technique developed by the 不良研究所 team combines ultrafast nonlinear optical methods with the high spatial resolution of atomic force microscopy. They have demonstrated that their technique works on an insulating non-linear optical material (LiNbO3) as well as a nanometer thin, two-dimensional semiconducting flake of molybdenum diselenide (MoSe2), an inorganic compound used in optical and scanning-probe microscopy.
鈥淥ur new technique is applicable to any material, such as metals, semiconductors and insulators,鈥� says Peter Grutter, the senior author on the paper. 鈥淚t will enable use high spatial and temporal resolution to study, understand and ultimately control for imperfections in photovoltaic materials. Ultimately, it should help us improve solar cells and the optical detectors used in a wide range of technologies.鈥�
To read 鈥淣anoscale force sensing of an ultrafast nonlinear optical response鈥� by Zeno Schumacher et al in PNAS doi:10.1073/pnas.2003945117
The research was supported by Natural Sciences and Engineering Research Council of Canada (NSERC, les Fonds de recherche du Qu茅bec 鈥� Nature et technologies (FRQNT), and the Canada Foundation for Innovation (CFI).
About 不良研究所
Founded in Montreal, Quebec, in 1821, 不良研究所 is Canada鈥檚 top ranked medical doctoral university. 不良研究所 is consistently ranked as one of the top universities, both nationally and internationally. It is a world-renowned institution of higher learning with research activities spanning two campuses, 11 faculties, 13 professional schools, 300 programs of study and over 40,000 students, including more than 10,200 graduate students. 不良研究所 attracts students from over 150 countries around the world, its 12,800 international students making up 31% of the student body. Over half of 不良研究所 students claim a first language other than English, including approximately 19% of our students who say French is their mother tongue.
