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Ultrafast Phenomena

This research is centered around the use of ultrafast lasers, that is, pulsed lasers that have a temporal width near 100 femtoseconds (10-13 seconds). This allows us to measure phenomena which occur on a very short time scale, by essentially "freezing" the motion of atoms and molecules.  Currently in use is a solid-state regeneratively amplified laser system producing 120 femtosecond pulses of 1 millijoule in energy, tunable in wavelength from 750nm to 900nm with a pulse repition rate of 1kHz.  The picture below illustrates a phenomenon called white-light continuum generation, in which an intense, femtosecond pulse (up to 1014W/cm2 in our case) is focused into a glass, liquid, or rare gas, to produce a coherent white light from the near-IR to the ultraviolet.  This is useful for time-domain spectroscopy applications, since any wavelength can be selected while preserving the ultrafast timescale of the pulses.

 
 
White light continuum produced in a 0.25" thick fused silica window
 

The Optical Physics and Engineering Lab has recently studied vibrational wavepackets in the Cesium dimer[1, 2, 3], which is used to independently verify (as opposed to traditional frequency-based methods) and improve upon the spectroscopic constants of the molecule.  Current studies involve the production of wavepackets in atomic media[4, 5, 6].  Specifically, we are using a four-wave mixing process in alkali-metal vapors to generate and detect wavepackets (that is, a superposition of states) which are populated by the large-bandwidth ultrafast laser pulses.  By using a pump-probe setup, we monitor the temporal evolution of the wavepackets by detecting the ultraviolet or violet light emitted as a result of the four-wave mixing process (see picture below).  This allows us to observe the wavepacket motion, which behaves as coupled pendula, with several "modes" (corresponding to energy level splittings) simultaneously oscillating as well as exchanging energy over longer timescales (tens of picseconds).  This energy exchange is an unexpected result which warrants further study, and may uncover new physics about the structure of the atom.
 
 

Violet emission at 420 nm from a heat pipe containing rubidium vapor at 2 torr,

pumped by 770 nm, 130 fs, 1 mJ energy light pulses.
 

Selected Papers:

C.J. Zhu, A.A. Senin,  Z.-H. Lu, J. Gao, Y. Xiao, and J.G. Eden, Physical Review A (Atomic, Molecular, and Optical Physics), v 72, n 2, 2005, p 23811-1-7. " Polarization of signal wave radiation generated by parametric four-wave mixing in rubidium vapor: ultrafast (~150-fs) and nanosecond time scale excitation"

C.J. Zhu, A.A. Senin, J. Gao, J.G. Eden, 2004 IEEE LEOS Annual Meeting Conference Proceedings, 2004, pt. 2, p 903-4 Vol.2. " Observation of quantum beating at 18.2 THz in Rb by parametric six-wave mixing"

C.J. Zhu, Z.H. Lu, A.A. Senin, J.R. Allen, A.L. Oldenburg, J. Gao, and J.G. Eden, International Quantum Electronics Conference (IQEC), 2004. " Competition between quantum beatings at 608 cm-1 and 70 cm-1 in Rb observed by parametric four-wave mixing"

J.G. Eden, Progress in Quantum Electronics, v 28, n 3-4, 2004, p 197-246. " High-order harmonic generation and other intense optical field-matter interactions: Review of recent experimental and theoretical advances"

Z.H. Lu, C.J. Zhu, A.A. Senin, J.R. Allen, J. Gao, and J.G. Eden, IEEE Journal on Selected Topics in Quantum Electronics, 10(1), 2004, Organic Light-Emitting Diodes, p 159-168. " Production and probing of atomic wavepackets with ultrafast laser pulses: Applications to atomic and molecular dynamics"

Senin, A.A.;  Tran, H.C.; Gao, J.; Lu, Z.H.; Zhu, C.J.; Oldenburg, A.L.; Allen, J.R.; Eden, J.G., Chemical Physics Letters, 381(1-2), 2003, p 53-9. "Molecular dissociation observed with an atomic wavepacket and parametric four-wave mixing"

Senin, A.A.; Lu, Z.H.; Zhu, C.J.; Allen, J.R.; Eden, J.G., Quantum Electronics and Laser Science (QELS). Postconference Digest (IEEE Cat No.CH37420-TBR), 2003, p 2 pp. " Observation of molecular dissociation along several exit channels with parametric four-wave mixing"

Senin, A.A.; Lu, Z.; Allen, J.R.; Eden, J.G., LEOS 2002. 2002 IEEE/LEOS Annual Meeting Conference Proceedings. 15th Annual Meeting of the IEEE Lasers and Electro-Optics Society (Cat. No.02CH37369), 2002, pt. 1, p 267-8 vol.1. "Ultrafast spectroscopic tool for studying molecular dissociation"

A. A. Senin, A. L. Oldenburg, and J. G. Eden, "Time-frequency analysis of the ultraviolet signal resulting from probe pulse scattering by atomic wavepackets."  presented at the 11th International Conference for Lasers in Science, Technology and Medicine, Sept. 2000, Sochi, Russia.

A. L. Oldenburg, P. C. John, and J. G. Eden, "Vibrational wavepackets in the B1Pu and D1Su+ states of Cs2: Determination of improved Cs2+(X) and Cs2(B) spectroscopic constants."  Journal of Chemical Physics  113, pp. 11009-18, 2000.

A. L. Oldenburg and J. G. Eden, "Wavepacket dynamics and time-domain spectroscopy in atomic rubidium."  [Conference Paper], Technical Digest, Quantum Electronics and Laser Sciences Conference, pp. 176-7, 1999.

H. C. Tran, P. C. John, and J. G. Eden, "Interaction of atomic wave packets with four-wave mixing: detection of rubidium and potassium wave packets by coherent ultraviolet emission."  Optics Letters  23, pp. 70-72, 1998.

G. Rodriguez, P. C. John, and J. G. Eden, "Vibrational wave packets in the C1Pu state of Cs2: Two color pump-probe expreiments."  Journal of Chemical Physics  103, pp. 10473-83, 1995.

G. Rodriguez and J. G. Eden, "Dynamics of vibrational wave packets in the C1Pu state of Cs2." Chemical Physics Letters  205, pp. 371-9, 1993.

 

ite maintained by Kwang Soo Kim (kkim28@uiuc.edu).  Copyright © 2004 Laboratory of Optical and Physics Engineering.

Administered by the Department of Electrical and Computer Engineering at the University of Illinois at Urbana-Champaign.