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Apr09-Editorial.pdf

The interaction of light with matter is probably the best diagnostic of matter that we have available to us. Quantum mechanics, for example, grew from such studies. Lasers control light. That is why they are so important. With lasers we are able to make light with a frequency purity of 1 part in 1015 and researchers are already discussing precision of 1 part in 1018. As a result of general relativity, a clock with this accuracy would be able to measure differences in the gravitational potential associated with a vertical shift of only a few millimetres! You may be surprised to learn that femtosecond pulses play a key role in accurate clocks. 

At the other Fourier transform extreme, we can make light flashes that last only 10-16 seconds (or just 100 attoseconds). The frequency content of ultrashort pulses is huge and the peak power of the pulses can be enormous. Imagine a light pulse lasting only about 10 femtosecond (10-14 sec) containing a joule of energy. Its power would be 1014 watts. In fact, such a laser is available at the International User Facility (ALLS) located at INRS near Montreal. Researchers in Europe are planning lasers containing 10’s or 100’s of joules! 1016 - 1017 W pulses appear feasible! In the section of Laser Science below, you will see two papers that highlight how the “Fourier transform twins” of very short or very high purity pulses are interrelated. 

Just as lasers allow us to control a beam in time, they also allow us to control it in space. In fact, lasers beams with a divergence at the very limit that the wave nature of light allows are common. Such beams can be focussed to a wavelength (or slightly below). If a 1017 W pulse were focussed to a micrometer, then the intensity of the beam at the focus would reach about 1025 W/cm2. God would have to think about how to respond -- he (or she) has no experience with such intensities! You will see below how extremely high power pulse like these might be used for a new generation of particle accelerators. University of Ottawa’s Thomas Brabec has also proposed that they can also open a method for measuring the dynamics of the nucleus [1]. 

The implications of these advances, and those that preceded them, lie everywhere in science -- in physics, chemistry, biology and engineering. It is impossible to cover all of the exciting activity in Canada in such a broad field. Instead, we have selected specific sub-topics that can represent the much more diverse effort. 

In biology and medicine, for example, researchers work on measuring the first steps in vision or photosynthesis, or they use lasers for new medical diagnostics and medical procedures. Instead of treating these subjects, we have chosen to represent biophotonics with microscopy and Optical Coherence Tomography. The significance of developments in these areas extends to all areas of science. 

In Chemistry, the impact of ultrafast lasers can be appreciated from the fact that the 1999 Nobel prize in Chemistry was awarded to Professor A. Zewail for femto-Chemistry. He applied the then new methods of laser science to time resolve key photochemical reactions. In this issue, Professor Bandrauk gives his overview of the implications of attosecond science for Chemistry. His overview will be accompanied by two complementary articles. One, by Professor Milner, discusses laser control of chemical reactions; the other, by Professor Siwick, uses femtosecond lasers to produce an ultrashort electron pulse. He uses these electrons to take a movie of melting solids. 

Ultrafast laser pulses are an invaluable tool to measure the dynamics response of solid state materials and in technology. Each of these is a very large field of research with important Canadian dimensions. For example, ultrafast methods are pervasive in optical telecommunications. We represent the technological applications of ultrafast pulses through two papers, one emphasizes the generation of terahertz radiation – opening a notoriously difficult region of the electromagnetic spectrum to applications. The other paper deals with laser micro-machining in dielectrics. 

It is a safe bet that every campus in Canada has advanced laser research. Some, such as the Université Laval, have made it their speciality. After you have looked over the articles in this issue, we suggest that you find out what work is most interesting on your campus. 

[1] N. Milosevic, P. B. Corkum and T. Brabec, “How to use Lasers for Imaging Attosecond Dynamics of Nuclear Processes”, Phys. Rev. Lett.., 92, 013002, (2004)

Paul B. Corkum, University of Ottawa/NRC
Mark Freeman, University of Alberta
Guest Editors, Physics in Canada

Comments of readers on this editorial are more than welcome.