Technical Activities

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"Technical Activities  2005-2007" - Table of Contents

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Quantum Physics Division
The strategy of the division is to help produce a new generation of scientists and to investigate new ways of precisely directing and controlling light, atoms, and molecules; measuring electronic, chemical, and biological processes and the nanoscale; and manipulating ultrashort light pulses.
GOAL: To make transfor- mational advances at the frontiers of measurement science, in partnership with the University of Colorado
at JILA.

Strategic Focus Areas:

   

First

Measurement Science  -  to develop precision measurement science tools and applications.

Second   

Ultracold Atoms and Molecules  -  to exploit Bose-Einstein condensation, quantum degenerate Fermi gases, and cold molecules for metrology and ultralow-temperature physics.

Third

Ultrafast Science  -  to advance ultrafast science.

Fourth

Biophysics  -  to apply cutting edge measurement science to biological physics.


Ultrafast Science:

to advance ultrafast science.

INTENDED OUTCOME AND BACKGROUND

Ultrafast science has traditionally exploited ultrashort optical pulses with durations as short as a few femtoseconds. These pulses provide precise time resolution and/or high peak powers. Because they are produced by modelocked lasers, their frequency comb spectra can be controlled with the techniques described in the first strategic element. In ultrafast science, the control of the comb spectrum corresponds to control of the electric field of the pulses in the time domain. Control of the electric field of the pulses enables the observation of unique physical phenomena and the ability to coherently synthesize new pulse shapes.

Traditional ultrafast techniques are used in the Division to study the dynamics of electron spins in semiconductors and of biomolecules, providing technologically important information for both optoelectronics and biotechnology. We use phase stabilization to improve measurement techniques and to develop radical new ultrafast technologies, such as "gainless" amplification of femtosecond pulses in a buildup cavity.

Accomplishments

  • Femtosecond Enhancement Cavities

    The use of femtosecond enhancement cavities continues to push the frontiers on wide-bandwidth molecular detections and VUV frequency comb generation. Optical frequency comb-based cavity-ringdown spectroscopy has recently enabled high sensitivity absorption detection of molecules over a broad spectral range.

    We have demonstrated an improved system based on a mode-locked erbium-doped fiber laser source centered at 1.5 μm, resulting in a spectrometer that is inexpensive, simple, and robust. It provides a very large spectral bandwidth (1.45 μm to 1.65 μm) for investigation of a wide variety of molecular absorption features. Strong molecular absorption at 1.5 μm allows for detection at sensitivities approaching the level of 1 nL/L. We have performed measurements of the rovibrational spectra for CO, NH3, H2O, and C2H2 with an absorption sensitivity of 10-8 cm-1Hz per detection channel. Spectral resolution has been dramatically improved to less than 100 MHz, easily useful for isotope identification.

    Femtosecond enhancement cavities can also be used to reach high intensities, which are usually achieved by using low repetition rate, expensive optical amplifiers. High-harmonic generation at 136 MHz r epetition rate has been produced with a cavity enhanced, Yb-fiber frequency-comb laser. The intracavity field peak intensity reaches above 3 × 1014 W/ cm2, corresponding to a record high 3.5 kW av erage power. We have demonstrated laser-induced plasmas and high-harmonic generation in Xe, Kr, and Ar. High-harmonic signals after an Al filter have been observed, thus it is clear that we are now reaching shorter wavelengths in comb generations than ever before.

    CONTACT: Dr. Jun Ye
    (303) 735-3171
    ye@jila.colorado.edu



    Figure 7

    Figure 7. Two-dimensional Fourier Transform spectra of exciton resonances in a GaAs heterostructure. (a) is experimental data, (b) is theory within a Hartree-Fock approximation, and (c) is a full theory including terms beyond Hartree-Fock.

  • Optical Two-Dimensional Fourier Transform Spectroscopy

    An optical two-dimensional Fourier transform spectrometer has been developed and is being used to study many-body effects in semiconductors. Multidimensional Fourier- transform spectroscopy was originally developed in nuclear magnetic resonance using radio frequencies. Recently there has been significant work to bring these techniques to infrared and optical frequencies. Achieving the necessary phase control and stability is a challenge. We have achieved it by using actively stabilized delay lines.

    Many-body effects in semiconductors were extensively studied using traditional ultrafast spectroscopic techniques. While the experimental results proved the nonlinear signals are dominated by many-body effects, they were unable to disentangle the various terms. Optical two-dimensional Fourier transform spectroscopy excels at separating the various contributions to the signals. The separation is in part due to the spreading of the signals in two dimensions and also because full phase information can be obtained. The experimentally obtained spectra have been compared to calculations and show good agreement, but only when terms beyond the standard Hartree-Fock approximation are included.

    A second-generation spectrometer is under development. It will allow all excitation pulses to be phase locked, not just two, as is the case for the current spectrometer. The new spectrometer will be used for continuing studies on semiconductors and for studies of atomic vapors and proteins.


    CONTACT: Dr. Steven T. Cundiff
    (303) 735-7858
    cundiff@jila.colorado.edu






  • Grism-Based, ScalableRepetition- Rate Ti:Sapphire Amplifier

    Working with academia and industry, Division scientists have developed efficient reflection grisms (gratings in contact with prisms) for pulse compression in femtosecond Ti:sapphire laser amplifiers. These components simplify and miniaturize the optics required for commonly used femtosecond amplifier systems. A simple and efficient grism-based femtosecond amplifier system that produces 36 fs, 300 μJ pulses at 5 kHz to 15 kHz repetition rates was demonstrated using the down-chirped pulse amplification technique.


    CONTACT: Dr. Ralph Jimenez
    (303) 492-8439
    rjimenez@jilau1.colorado.edu


First strategic focus | Second strategic focus | Third strategic focus | Fourth strategic focus

"Technical Activities  2005-2007" - Table of Contents