SC439 - Attosecond Optics
Sunday, 13 May
13:30 - 16:30
Short Course Level: Beginner (No background or minimal training is necessary to understand course material)
Zenghu Chang, Univ. of Central Florida, USA
Short Course Description:
Since the invention of lasers in 1960, various techniques such as mode-locking have been developed to push the pulse duration down first to picoseconds and then to femtoseconds, which is the oscillation period of infrared and visible light. The generation of attosecond pulses requires new methods to produce broadband coherent electromagnetic waves in the UV to X-ray range because of the lack of proper gain media. The discovery of high-order harmonic generation in high intensity laser-atom interaction at the end of 1980s paved the way. In 2001, attosecond light pulses, a train of attosecond bursts or single isolated attosecond pulses, were measured for the first time. It was accomplished by first converting the attosecond photons to photoelectrons in a combination of weak extreme ultraviolet and strong infrared fields, and then retrieve the spectral phase of the attosecond pulse by reconstructing the photoelectron spectrum. Since then, various sub-optical-cycle gating schemes such as polarization gating and Double Optical Gating have been demonstrated to generation isolated attosecond pulses. By properly compensating the intrinsic chirp, 53 as pulses were characterized in 2017, which is so far the shorted light pulses. The new frontier in attosecond optics research is to significantly increase the photon flux and to extend the spectrum to the “water window.” This course covers: (1) High harmonic generation. (2) Carrier-envelope phase of femtosecond driving lasers. (3) Semi-classical model and Strong Field Approximation. (4) Phase-matching in partially ionized media. (5) Sub-cycle gating and attosecond pulse characterization. (6) Attosecond streaking and transient absorption spectroscopy.
Short Course Benefits:
This course should enable participants to:
Specify parameters of femtosecond driving lasers that are critical to the generation of attosecond pulse trains and single isolated attosecond pulses,
Compare pros and cons of driving lasers based on Ti:Sapphire Chirped Pulse Amplification and Optical Parametric Amplifiers.
Explain the principle and techniques of locking the carrier-envelope offset frequency of femtosecond oscillators and carrier-envelope phase of amplified pulses.
Define short and long trajectories in the attosecond generation process using the Strong Field Approximation in the Lewenstein model.
Estimate the cutoff photon energy and attosecond chirp using the semi-classical model.
Calculate ionization probability of atoms in an intense laser field with the Ammosov-Delone-Krainov (ADK) tunneling rate.
Describe the principle of attosecond streak camera for characterizing attosecond pulses, as well as identify the major factors that affects the phase matching of high harmonic generation in partially ionized media.
Short Course Audience:
This short course targets senior undergraduate students, graduate students, postdoc fellows, scientists and engineers seeking to enter attosecond optics. The audience should have studied electromagnetism, optics, lasers, quantum mechanics and atomic physics at undergraduate or graduate levels. Prior knowledge of femtosecond lasers is required. Although basic theory is covered, it emphasizes on experimental aspects of attosecond optics, such as locking the carrier-envelope phase of the driving lasers and designing time-of-flight spectrometers for attosecond streak cameras.
Zenghu Chang is a Trustee Chair and Distinguished Professor at the University of Central Florida, where he directs the Institute for the Frontier of Attosecond Science and Technology. His group generated the shortest laser pulses, 53 as, which is the current world record. He is the author of the book “Fundamentals of Attosecond Optics.”