Nicholas Karpowicz

Max Planck Institute of Quantum Optics, Arching, Bavaria, Germany

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Publications (36)129.45 Total impact

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    ABSTRACT: The dynamics of chirped pulse amplification in thin-disk regenerative amplifiers relevant to the pumping of optical parametric chirp pulse amplification systems are described. It is shown that the suitability for reproducible pumping of subsequent nonlinear processes requires a balance between the demands of avoiding chaotic pulse train dynamics and providing a reproducible spectral phase. We describe measures that may be taken to ensure that a laser system operates in the desired stable regime.
    Optics Express 12/2014; 22(25). · 3.55 Impact Factor
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    ABSTRACT: Femtosecond pulse generation was pioneered four decades ago using mode-locked dye lasers, which dominated the field for the following 20 years. Dye lasers were then replaced with titanium-doped sapphire (Ti:Sa) lasers, which have had their own two-decade reign. Broadband optical parametric amplifiers (OPAs) appeared on the horizon more than 20 years ago but have been lacking powerful, cost-effective picosecond pump sources for a long time. Diode-pumped ytterbium-doped solid-state lasers are about to change this state of affairs profoundly. They are able to deliver 1 ps scale pulses at kilowatt-scale average power levels, which, in thin-disk lasers, may come in combination with terawatt-scale peak powers. Broadband OPAs pumped by these sources hold promise for surpassing the performance of current femtosecond systems so dramatically as to justify referring to them as the next generation. Third-generation femtosecond technology (3FST) offers the potential for femtosecond light tunable over several octaves, multi-terawatt few-cycle pulses, and synthesized multi-octave light transients. Unique tunability, temporal confinement, and waveform variety in combination with unprecedented average powers will extend nonlinear optics and laser spectroscopy to previously inaccessible wavelength domains, ranging from the far IR to the x-ray regime. Here we review the underlying concepts, technologies, and proof-of-principle experiments. A conceptual design study of a prototypical tunable and wideband source demonstrates the potential of 3FST for pushing the frontiers of femtosecond and attosecond science.
    Optica. 07/2014; 1(1):45-63.
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    ABSTRACT: We present experimental observations and corresponding numerical simulations illustrating the difference-frequency generation of mid-infrared radiation using few-cycle near-infrared-to-visible pulses, which yields conversion efficiencies above 12% in beta-barium borate crystal. Type I and type II phase-matching are shown to yield qualitatively different intensity-scaling behavior, with the former showing higher overall efficiency, especially with the addition of a zero-order wave plate for modifying the polarization state of the pulse, and the latter having a better stability of the spectrum versus input intensity.
    Optics Letters 10/2013; 38(20):4216-9. · 3.39 Impact Factor
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    ABSTRACT: Attosecond science relies on the use of intense, waveform-controlled, few-cycle laser pulses1 to control extreme nonlinear optical processes taking place within a fraction of an optical period. A number of techniques are available for retrieving the amplitude envelope and chirp of such few-cycle laser pulses. However, their full characterization requires detection of the absolute offset between the rapidly oscillating carrier wave and the pulse envelope, the carrier–envelope phase (CEP). So far, this has only been feasible with photoelectron spectroscopy, relying on complex vacuum set-ups2, 3, 4. Here, we present a technique that enables the detection of the CEP of few-cycle laser pulses under ambient conditions. This is based on the CEP-dependence of directly measurable electric currents generated by the electric field of light in a metal–dielectric–metal nanojunction. The device holds promise for routine measurement and monitoring of the CEP in attosecond laboratories.
    Nature Photonics 07/2013; · 27.25 Impact Factor
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    ABSTRACT: form only given. High-energy, ultrashort pulses in the few-cycle regime are of great interest as drivers of intense attosecond-pulse sources [1]. Noncollinear optical parametric chirped pulse amplification (OPCPA) is a promising technique to reach an ultrabroad amplification bandwidth and high pulse energies, simultaneously. Recently, in our laboratory a 3-stage OPCPA system delivering pulses with a bandwidth ranging from 670-1400 nm and a pulse energy of 1.8 mJ at 3 kHz repetition rate has been demonstrated [2]. This ultrabroadband amplified spectrum supports 4.3 fs pulses, with a central wavelength around 1 μτη. In this study we investigate the possibility of pulse compression by double-angle chirped mirrors [3].In order to compress the pulse to its transform limit, the chromatic dispersion introduced by the gain media and other dispersive components along the optical path needs to be compensated. In our system we take into account 3 mm FS, 2 mm of BaF2 (of a cross-polarized wave generation stage added to the setup described in [2]), 6 mm LBO, 2 mm BBO and several metres of air. We have calculated the resulting group delay (GD) and group delay dispersion (GDD) according to the Sellmeier equations. The resulting GD curve with opposite sign represents the target curve for the mirror design of the compressor, since the GD of the system and the double-angle chirped-mirror compressor add up linearly. In the double-angle chirped-mirror technique one multilayer design allows for the compensation of GDD oscillations by using reflections under two distinct angles of incidence. In this sense the mirrors have to be used in “pairs” in order to obtain the lowest possible oscillations. The result of the design in terms of the GDD for one such pair, i.e. one mirror used under 5o and one used under 21o angle of incidence, is shown in the central panel of Fig. 1. For such a broadband chirped mirror it is common- even after the compensation using the double-angle technique to have relatively high residual GDD oscillations. However, by analyzing the corresponding GD, which is obtained by numerically integrating the GDD curve once with respect to frequency, we can see that these large oscillations translate into relatively small ripples on the GD curve. This is shown on the left in Fig. 1 where the GD curves for four and five pairs are compared with the target curve. The good match between the design and the target together with the small resulting GD oscillation theoretically allow for a compression with this device to close to the transform limit of the amplified spectrum. This can be seen in Fig. 1 (right), where the compression of a supergaussian spectrum (670 - 1400 nm) to 4.6 fs has been calculated using the GD of 5 pairs. The experimental implementation of the compressor is currently under way, however the full characterization of such an ultrabroad spectrum with close to single-cycle pulse duration is far from straightforward. While in the past a second harmonic (SHG) FROG (frequency-resolved optical gating) was used, in the future we plan to implement a Transient-Grating (TG) FROG device [4], which in our case will overcome the significant bandwidth limitations and phase-matching constraints of the SHG-FROG.
    2013 Conference on Lasers & Electro-Optics Europe & International Quantum Electronics Conference CLEO EUROPE/IQEC; 05/2013
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    ABSTRACT: We investigate the influence of carrier cooling dynamics in TiO_{2} on the excited-state potential energy surface along the A_{1g} optical phonon coordinate after above band-gap excitation using ultrashort ultraviolet pulses. The large amplitude coherent oscillation observed in a pump-probe transient reflectivity measurement shows a phase shift of -0.2π with respect to a purely instantaneous displacive excitation. The dynamic evolution of the potential energy surface minimum of the coherent phonon coordinate is explored using accurate density functional theory calculations, which confirm a shift of the potential energy surface minimum upon resonant laser excitation and reveal a significant positive contribution to the displacive force due to the cooling of the excited hot electron-hole plasma. We show that this noninstantaneous effect can quantitatively explain the experimentally observed phase using reasonable assumptions for the parameters characterizing the excited carriers. Our work demonstrates that the fast equilibration dynamics of laser-excited nonequilibrium carrier populations can have a pronounced effect on the initial structural response of crystalline solids.
    Physical Review Letters 02/2013; 110(6):067402. · 7.73 Impact Factor
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    ABSTRACT: The time it takes to switch on and off electric current determines the rate at which signals can be processed and sampled in modern information technology. Field-effect transistors are able to control currents at frequencies of the order of or higher than 100 gigahertz, but electric interconnects may hamper progress towards reaching the terahertz (10(12) hertz) range. All-optical injection of currents through interfering photoexcitation pathways or photoconductive switching of terahertz transients has made it possible to control electric current on a subpicosecond timescale in semiconductors. Insulators have been deemed unsuitable for both methods, because of the need for either ultraviolet light or strong fields, which induce slow damage or ultrafast breakdown, respectively. Here we report the feasibility of electric signal manipulation in a dielectric. A few-cycle optical waveform reversibly increases-free from breakdown-the a.c. conductivity of amorphous silicon dioxide (fused silica) by more than 18 orders of magnitude within 1 femtosecond, allowing electric currents to be driven, directed and switched by the instantaneous light field. Our work opens the way to extending electronic signal processing and high-speed metrology into the petahertz (10(15) hertz) domain.
    Nature 12/2012; · 38.60 Impact Factor
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    ABSTRACT: We produce 1.5 cycle (10.5 fs), 1.2 mJ, 3 kHz carrier-envelope-phase-stable pulses at 2.1 μm carrier wavelength, from a three-stage optical parametric chirped-pulse amplifier system, pumped by an optically synchronized 1.6 ps Yb:YAG thin disk laser. A chirped periodically poled lithium niobate crystal is used to generate the ultrabroad spectrum needed for a 1.5 cycle pulse through difference frequency mixing of spectrally broadened pulse from a Ti:sapphire amplifier. It will be an ideal tool for producing isolated attosecond pulses with high photon energies.
    Optics Letters 12/2012; 37(23):4973-5. · 3.39 Impact Factor
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    ABSTRACT: The interaction of a few-cycle laser pulse with a metal-dielectric nanostructure creates measurable electric currents. We show that the time scale of the process is sufficiently fast to sample oscillations at visible light frequencies.
    Laser Science; 10/2012
  • Benjamin Clough, Nicholas Karpowicz, X.-C. Zhang
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    ABSTRACT: A synthesized fundamental optical beam and its second harmonic laser field is phase modulated to dynamically reshape the electron momentum distribution inside an air-plasma filament. The net electron motion becomes a combination of the initial laser “kick,” from the remaining optical field, and the terahertz field present at the time of its ionization. The time dependent Schrödinger equation is solved to map the net electron velocity distribution as the phase between the two color beams is changed, and single-scan coherent terahertz wave detection through air-plasma fluorescence is experimentally demonstrated.
    Applied Physics Letters 03/2012; 100(12). · 3.52 Impact Factor
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    ABSTRACT: The fast oscillating electric field of intense few-cycle near-infrared laser pulses with well-defined carrier-envelope phase is exploited to generate charge carriers and control their ultrafast motion within heterogeneous nanoscaled solid-state interfaces.
    Nonlinear Optics: Materials, Fundamentals and Applications; 07/2011
  • Jianming Dai, Nicholas Karpowicz, X-C Zhang
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    ABSTRACT: Unlike polarization control of optical waves, lossless control over the polarization of broadband terahertz waves remained challenging. We recently found that the polarization of terahertz waves generated from gas plasma excited by femtosecond fundamental pulse (ω) and its second harmonic (2ω) could be coherently controlled by changing the relative phase between the ω and 2ω pulses. In particular, when the ω and 2ω pulses are both circularly polarized (or close to it), the photo-excited electrons exhibit different trajectories as the relative phase between the two optical pulses changes, and subsequently terahertz polarization angle can be controlled arbitrarily through the relative phase while the intensity of the emitted terahertz wave is kept constant. This new finding may enable fast terahertz wave modulation and coherent control of nonlinear responses excited by intense terahertz waves with controllable polarization.
    Journal of Physics Conference Series 03/2011; 276(1):012003.
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    ABSTRACT: We report on time-resolved experiments to investigate the attosecond dynamics of photoelectrons generated by ultra-short XUV pulses on clean metal surfaces and in well-defined adsorbate-metal interfaces.
    International Conference on Ultrafast Phenomena; 07/2010
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    ABSTRACT: We demonstrate generation and measurement of intense deep-ultraviolet light pulses with a duration of approximately 2.8 fs (FWHM of the intensity envelope) and a wavelength distribution between 230 and 290 nm. They emerge via direct frequency upconversion of sub-4 fs laser pulses of a carrier wavelength of approximately 750 nm focused into an Ne-filled, quasi-static gas cell. Dispersion-free, third-order autocorrelation measurements provide access to their temporal intensity profile.
    Optics Letters 07/2010; 35(13):2248-50. · 3.39 Impact Factor
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    ABSTRACT: Attosecond streaking, as a measurement technique, was originally conceived as a means to characterize attosecond light pulses, which is a good approximation if the relevant transition matrix elements are approximately constant within the bandwidth of the light pulse. Our analysis of attosecond streaking measurements on systems with complex response to the photoionizing pulse establishes a relation between the momentum-space wave function of the outgoing electron and the result of conventional retrieval algorithms. This finding enables the measurement of the quantum phase associated with bound-continuum transition matrix elements. Comment: similar to the version accepted for publication in PRL
    Physical Review Letters 06/2010; · 7.73 Impact Factor
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    Jianming Dai, Jingle Liu, I-Chen Ho, Nicholas Karpowicz, X.-C. Zhang
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    ABSTRACT: We present experimental and theoretical investigations on the THz wave generation and detection using ambient air or selected gases as the THz emitter and sensor, as well as the potential applications of THz air photonics.
    05/2010;
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    Jianming Dai, Nicholas Karpowicz, X.-C. Zhang
    Optics and Photonics News 12/2009; 20(12):36.
  • Xiaofei Lu, Nicholas Karpowicz, X.-C. Zhang
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    ABSTRACT: We present a combined theoretical and experimental investigation of the detection of pulsed terahertz waves via field-induced second-harmonic generation in gaseous media. The effects of the probe pulse energy, bias field strength, nonlinear susceptibility of the gases, phase matching, and focusing conditions of the terahertz and optical beams are discussed. The analytical calculation, which is based on a Gaussian-beam approximation, allows for the easy identification of the parameters important for the sensitivity of the terahertz gas sensor. A figure of merit is introduced to characterize the sensitivity of gases. The experimental results are found to be in good agreement with the calculation.
    Journal of the Optical Society of America B 08/2009; 26(9):A66-A73. · 2.21 Impact Factor
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    Jianming Dai, Nicholas Karpowicz, X-C Zhang
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    ABSTRACT: Electrons ionized from an atom or molecule by circularly or elliptically polarized femtosecond omega and 2omega pulses exhibit different trajectory orientations as the relative phase between the two pulses changes. Macroscopically, the polarization of the terahertz wave emitted during the ionization process was found to be coherently controllable through the optical phase. This new finding can be completely reproduced by numerical simulation and may enable fast terahertz wave modulation and coherent control of nonlinear responses excited by intense terahertz waves with controllable polarization.
    Physical Review Letters 08/2009; 103(2):023001. · 7.73 Impact Factor
  • Nicholas Karpowicz, Xiaofei Lu, X.-C. Zhang
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    ABSTRACT: The underlying physics of the generation and detection of terahertz (THz) waves in gases are described. The THz wave generation process takes place in two steps: asymmetric gas ionization by two-frequency laser fields, followed by interaction of the ionized electron wave packets with the surrounding medium, producing an intense ‘echo’ with tunable spectral content. In order to clarify the physical picture at the moment of ionization, the laser–atom interaction is treated through solution of the time-dependent Schrödinger equation, yielding an ab initio understanding of the release of the electron wave packets. The second step, where the electrons interact with the surrounding plasma is treated analytically. The resulting pressure dependence of the THz radiation is explored in detail. The THz wave detection process is shown to be the result of four-wave mixing, leading to analytical expressions of the signal obtained which allow for improved optimization of systems that exploit these effects.
    Journal of Modern Optics 01/2009; 56(10):1137-1150. · 1.16 Impact Factor