Donna Strickland: Nobel Lecture in Physics 2018

Transcript

our next speaker is Donna Strickland Donna is a Canadian experimental physicist born in May 1959 in the City of Guelph in southwestern Ontario she received her bachelor's degree in engineering physics from McMaster University in Canada in 1981 and obtained a PhD in optics from the University of Rochester New York in 1999 where she and her doctoral ... Read More

Summary

Donna Strickland, a Canadian experimental physicist, discusses how light interacts with matter and how intense light can change this interaction. She explains the concept of photons and their energy, and how different colors of light have varying effects on electrons. She also discusses the work of Albert Einstein and Maria Goeppert-Mayer in understanding the quantized nature of light energy and the concept of multiphoton ionization. Strickland then describes her own research in developing intense laser pulses using chirped pulse amplification (CPA) technique. She explains the process of pulse stretching and amplification using laser rods, gratings, and optical fibers. Finally, she discusses her experiments with multiphoton ionization and the unexpected behavior of intense laser light interacting with atoms.

Questions & Answers

Q: How did early scientists investigate the interaction between light and matter?

Early scientists wondered whether light was made up of particles or waves. They shone different colors of light on materials and observed the behavior of electrons being ejected. Initially, they believed that red light did not cause electrons to come off, while green light caused electrons to come off but with low speed. However, violet light caused electrons to come off with higher speeds.

Q: How did Albert Einstein contribute to the understanding of light energy?

Albert Einstein explained the observation that light energy was quantized into individual photons. He proposed that light was made up of particles called photons, and the energy of a photon was determined by its wavelength. He received a Nobel Prize for his explanation of the photoelectric effect, which demonstrated that light energy was carried by discrete packets or quanta.

Q: What did Maria Goeppert-Mayer contribute to the study of light and matter interaction?

Maria Goeppert-Mayer's research focused on the concept of multiphoton ionization, which involves the interaction of multiple photons with atoms. She hypothesized that if multiple photons could interact with an atom simultaneously, they could collectively provide enough energy to liberate an electron. However, her idea was not immediately observed experimentally, and it took several decades before her predictions were confirmed.

Q: How were multiphoton effects finally observed?

It was not until the 1960s, with the invention of the laser, that researchers were able to observe multiphoton effects. The first experimental observation of multiphoton ionization was done by Peter Franken's group at the University of Michigan in 1961, using atoms that temporarily absorbed two red photons and emitted one photon with double the energy. This phenomenon is known as second harmonic generation.

Q: What is the difference between a regular light source and laser light?

Regular light sources emit photons of all colors in random directions, which results in low photon density and lack of coherence. Laser light, on the other hand, is a single-color, highly coherent beam of photons. In a laser, the photons are in phase and work together to create a concentrated, directed beam of light.

Q: How did Donna Strickland and Gerard Mourou develop intense laser pulses?

Donna Strickland and Gerard Mourou developed a technique called chirped pulse amplification (CPA). They started with a short laser pulse and stretched it out using a process called pulse stretching. Then, they amplified the stretched pulse, which increased its energy. Finally, they compressed the amplified pulse back to its original duration using gratings. This process allowed them to create intense laser pulses with high peak power.

Q: Why did Donna Strickland need fiber optics in her laser experiment?

Donna Strickland used fiber optics in her experiment for several reasons. Firstly, she needed more colors in her laser beam to create a shorter pulse. By adding different wavelengths of light in the fiber, the pulse could be stretched to a greater extent. Secondly, the fiber allowed her to transport the laser beam to another part of the laboratory, where she built the laser amplifier. Finally, fiber optics helped to avoid damage caused by nonlinear effects that occurred inside laser rods.

Q: How did Donna Strickland use pulse compression to shorten the laser pulse again?

Pulse compression was achieved using a pair of parallel gratings, which act like prisms to separate light of different colors. As the stretched pulse passed through the gratings, the different colors were sent out at different angles, with the red color leading the way and the blue color trailing behind. When the colors passed through the second grating, they all converged at the same time, resulting in a compressed, short pulse.

Q: What was Donna Strickland's initial goal for the intense laser pulses?

Donna Strickland's initial goal was to study harmonic generation using intense laser pulses. She wanted to explore the possibility of grabbing multiple photons with one atom to generate higher energy photons. Specifically, she aimed to use nine photons to ionize twice ionized nickel. However, due to technical difficulties and the limitations of the CPA technique, she shifted her focus to multiphoton ionization.

Q: How did intense laser light interact with matter in Donna Strickland's experiments?

In Donna Strickland's experiments, the intense laser light created a giant wave-like structure with high photon density. This wave interacted with atoms, causing them to be pushed and pulled by the electric field of the light. The interaction was so strong that electrons were released from the atoms and accelerated by the electric field. This resulted in the emission of high-energy particles within femtoseconds.

Takeaways

Donna Strickland's research in developing intense laser pulses using chirped pulse amplification (CPA) technique has revolutionized the field of laser science. She demonstrated how light interacts with matter and how intense light can change this interaction. The CPA technique allows researchers to create high-intensity laser pulses with short durations and high photon density. This has opened up new possibilities for studying light-matter interactions and has led to advancements in various fields, including medicine and eye treatment. Strickland's work highlights the importance of pushing the boundaries of scientific understanding and continually innovating in the field of laser science.