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ABSTRACT: An extended cavity Ti:Sapphire oscillator exhibits stable operation for positively chirped pulses, while in the negative chirp regime multiple pulses are present in the cavity. At the border of these regimes automodulations, being an effect of the interplay between population inversion, laser medium polarization and the laser pulse field, appear. Two particular instabilities: period doubling and chaotic behavior of the pulse train envelope are observed. Complex temporal evolution of the pulse spectrum within the modulation period is investigated.
Optics Express 12/2010; 18(26):26989-94. · 3.59 Impact Factor
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ABSTRACT: Manipulation of quantum interference requires that the system under control remains coherent, avoiding (or at least postponing) the phase randomization that can ensue from coupling to an uncontrolled environment. We show that closed-loop coherent control can be used to mitigate the rate of quantum dephasing in a gas-phase ensemble of potassium dimers (K2), which acts as a model system for testing the general concepts of controlling decoherence. Specifically, we adaptively shaped the light pulse used to prepare a vibrational wave packet in electronically excited K2, with the amplitude of quantum beats in the fluorescence signal used as an easily measured surrogate for the purpose of optimizing coherence. The optimal pulse increased the beat amplitude from below the noise level to well above it, and thereby increased the coherence life time as compared with the beats produced by a transform-limited pulse. Closed-loop methods can thus effectively identify states that are robust against dephasing without any previous information about the system-environment interaction.
Science 06/2008; 320(5876):638-43. · 31.20 Impact Factor
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ABSTRACT: We present an experimental demonstration of heralded single photons prepared in pure quantum states from a parametric down-conversion source. It is shown that, through controlling the modal structure of the photon pair emission, one can generate pairs in factorable states and thence eliminate the need for spectral filters in multiple-source interference schemes. Indistinguishable heralded photons were generated in two independent spectrally engineered sources and Hong-Ou-Mandel interference observed between them without spectral filters. The measured visibility of 94.4% sets a minimum bound on the mean photon purity.
Physical Review Letters 04/2008; 100(13):133601. · 7.37 Impact Factor
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ABSTRACT: We present experimental data of the frequency-resolved optical gating measurements of light pulses revealing interference features which correspond to sub-Planck structures in phase space. For superpositions of pulses, a small, sub-Fourier shift in the carrier frequency leads to a state orthogonal to the initial one, although in the representation of standard time-frequency distributions these states seem to have a nonvanishing overlap.
Physical Review Letters 03/2007; 98(6):063901. · 7.37 Impact Factor
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ABSTRACT: A simple, compact, and robust implementation of spectral shearing interferometry using a single nonlinear crystal for both ancilla generation and upconversion is demonstrated. The device is capable of accurate characterization of femtosecond laser pulses over the 740-900 nm range with a KDP crystal.
Optics Letters 02/2007; 32(2):181-3. · 3.40 Impact Factor
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ABSTRACT: We propose and demonstrate a novel implementation of spectral-shearing interferometry (SSI) for reconstructing the electric field of ultrashort pulses by utilizing asymmetric group velocity matching in a long nonlinear crystal. The proposed configuration eliminates the requirement for a linearly chirped auxiliary pulse that is in common in all existing SSI methods, relying on nonlinear conversion to produce a spectral shear.
Optics Letters 05/2006; 31(7):1008-10. · 3.40 Impact Factor
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ABSTRACT: We propose and demonstrate a method for measuring the joint spectrum of photon pairs via Fourier spectroscopy. The biphoton spectral intensity is computed from a two-dimensional interferogram of coincidence counts. The method has been implemented for a type-I downconversion source using a pair of common-path Mach-Zehnder interferometers based on Soleil compensators. The experimental results agree well with calculated frequency correlations that take into account the effects of coupling into single-mode fibers. The Fourier method is advantageous over scanning spectrometry when detectors exhibit high dark count rates leading to dominant additive noise.
Optics Letters 05/2006; 31(8):1130-2. · 3.40 Impact Factor
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ABSTRACT: A compact, single-shot, second-harmonic autocorrelator for ultrashort laser pulse measurements is presented. The autocorrelator uses a Babinet compensator to split the pulse to be measured into two replicas with a relative delay between them varying across the beam. It consists of a few optical elements only, requires no sensitive alignment, and offers a robust diagnostics tool for low repetition rate femtosecond laser amplifiers. © 2004 American Institute of Physics.
Review of Scientific Instruments 06/2004; 75(7):2482-2484. · 1.37 Impact Factor
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ABSTRACT: Ultrakurze optische Pulse sind in vielen Bereichen ein zunehmend wichti-ges Werkzeug. Manchmal sind die extrem hohen elektrischen Feldstärken der Pulse nützlich, während unter anderen Umständen die Pulsdauer selbst entscheidend ist. In beiden Fällen gilt: Kann man das elektrische Feld des Pulses in seinem zeitlichen Verlauf (oder frequenzabhängig) vollständig cha-rakterisieren, dann erweitert dies den Wirkungsbereich von Techniken zur Beschreibung ultraschneller Phänomene. So lassen sich nicht nur völlig neu-artige Experimente durchführen, sondern auch die Reichweite und Zuver-lässigkeit konventioneller optischer Ultrakurzpuls-Techniken vergrößern. Der weit verbreitete Einsatz ultraschneller Technologien in Physik, Chemie, Biologie und Medizin sowie ihre Schlüsselrolle in zahlreichen praktischen Anwendungen verlangt nach der Entwicklung von Instru-menten zur Puls-Charakterisierung, die mindestens so stabil sind wie die derzeiti-gen Laserquellen. Diese Messgeräte sollten hochempfi ndlich sein, außerdem einfach anzuwenden, fl exibel und zuverlässig. Der kürzlich entwickelte micro-SPIDER (Bild 1) ist ein solches Instrument.
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ABSTRACT: Ultrashort optical pulses form an increasingly important tool for many fields. In some cases it is the ability to deliver extremely high electric field strengths that makes the pulses useful, whilst in others it is the duration of the pulse itself that is critical. In both circumstances the ability to completely characterize the pulse's electric field in time (or frequency) adds a new dimension to ultra-fast science, providing the means to perform new types of experiments and extending the range and reliability of standard ultrafast optical techniques. The widespread use of ultrafast technology in physics, chemistry, biology, medicine and its enabling role in numerous practical applications calls for the development of pulse characterization instrumentation that is at least as robust as the current genera-tion of laser sources. This instrumentation should be extremely sensitive, easy to use, flexible and reliable. The recently devel-oped microSPIDER shown in figure 1 is such a device.
