N. Karpowicz

Rensselaer Polytechnic Institute, Troy, New York, United States

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Publications (19)24.3 Total impact

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    ABSTRACT: The significant scientific and technological potential of terahertz (THz) wave sensing and imaging has been attracted considerable attention within many fields of research. However, the development of remote, broadband THz wave sensing technology is lagging behind the compelling needs that exist in the areas of astronomy, global environmental monitoring, and homeland security. This is due to the challenge posed by high absorption of ambient moisture in the THz range. Although various time-domain THz detection techniques have recently been demonstrated, the requirement for an on-site bias or forward collection of the optical signal inevitably prohibits their applications for remote sensing. The objective of this paper is to report updated THz air-plasma technology to meet this great challenge of remote sensing. A focused optical pulse (mJ pulse energy and femtosecond pulse duration) in gas creates a plasma, which can serve to generate intense, broadband, and directional THz waves in the far field.
    Proc SPIE 11/2010;
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    J M Dai, X F Lu, J Liu, I C Ho, N Karpowicz, X.-C Zhang
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    ABSTRACT: Historically, THz technologies were mainly used within the astronomy community for studying cosmic far-infrared radiation background, and by the laser fusion community for the diagnostics of plasmas. Since the first demonstration of THz wave time-domain spectroscopy in the late 80's, there has been a series of significant advances (particularly in recent years) as more intense THz sources and more sensitive detectors provide new opportunities for understanding the basic science in the THz frequency range. Now, the region of the electromagnetic spectrum from 0.3 to 10 THz (1 mm – 30 μm wavelength) is a frontier for research in physics, chemistry, biology, materials science and medicine. Ambient air, when excited with intense femtosecond laser beams, exhibits a remarkable ability to generate and detect pulsed THz waves through an optical nonlinear process. The use of air (or selected gases) as a broadband THz wave emitter and THz wave sensor provides superior bandwidth (0.5 -20 THz at 10% bandwidth), sensitivity (heterodyne), resolution (<MHz), and the standoff sensing capability in atmosphere which was heretofore considered impossible due to water vapor attenuation. However, research into the basic science and engineering of THz waves in laser-induced air plasma, especially the application of wide-band and high-field THz waves with standoff capability, is just beginning. Our proposed instrumentation development explores this new area, with an emphasis on broadband spectroscopy, remote sensing and nonlinear effect.
    Terahertz Science and Technology. 01/2010; 2:1941-7411.
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    Jianming Dai, N. Karpowicz, X.-C. Zhang
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    ABSTRACT: We present recent results on experimental measurements and theoretical simulations for terahertz wave generation (quantum mechanical simulation) and detection (four-wave-mixing) with ambient air and selected gases. We demonstrate standoff terahertz wave generation for potential applications of terahertz air photonics in remote sensing and identification.
    Infrared, Millimeter, and Terahertz Waves, 2009. IRMMW-THz 2009. 34th International Conference on; 10/2009
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    ABSTRACT: We present a multiwavelength phase imaging method for terahertz (THz) reflective focal-plane imaging. The phase of the THz pulse at each pixel is linearly fitted within the effective frequency range to reconstruct the ranging profile of the object. The results show that the multiwavelength method significantly improves the ranging resolution and imaging quality in THz reflective imaging applications.
    Journal of the Optical Society of America A 06/2009; 26(5):1187-90. · 1.67 Impact Factor
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    N Karpowicz, X-C Zhang
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    ABSTRACT: We study tunnel ionized electron wave packet dynamics during the initial transition from a gas to a plasma by detecting the terahertz radiation emitted in the process. Experimental and theoretical results show that much of the observed radiation is due to coherent buildup of bremsstrahlung released during the first electron-atom collision. Coherent control of the tunnel ionization process combined with ab initio modeling provides a real-time view of the initial stages of the formation of a laser-induced plasma and allows us to fully understand this important source of terahertz radiation.
    Physical Review Letters 04/2009; 102(9):093001. · 7.94 Impact Factor
  • N. Karpowicz, Xiaofei Lu, X. -C. Zhang
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    ABSTRACT: The role of tunnel ionization in the generation and detection of terahertz waves in gases is explored both theoretically and experimentally. It is shown through comparison of their respective intensity dependence trends that only the generation process requires ionization of the gas, helping to elucidate the difference in the underlying physical mechanisms. This difference in power dependence shows good agreement with quantum mechanical modeling based on solving the time-dependent Schrodinger equation. In the case of detection, the behavior is well described by four-wave mixing, a result of third order perturbation theory.
    Laser Physics 01/2009; 19(8):1535-1539. · 2.55 Impact Factor
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    ABSTRACT: We present a real time imaging measurement in the terahertz (THz) frequency region. The dynamic subtraction technique is used to reduce long-term optical background drift. The reflective images of two targets, a Nikon camera's lens cap and a plastic toy gun, are obtained. For the lens cap, the image data were processed to be false color images. For the toy gun, we show that even under an optically opaque canvas bag, a clear terahertz image is obtained. It is shown that terahertz real time imaging can be used to nondestructively detect concealed objects.
    Proc SPIE 03/2008;
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    ABSTRACT: Terahertz generation from gaseous media was further investigated by a gas jet system. The experimental results reveal that the terahertz radiation amplitude is correlated with the third order nonlinear susceptibility.
    01/2008;
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    ABSTRACT: We present a real-time imaging measurement in the terahertz (THz) frequency region. The dynamic subtraction technique is used to reduce long-term optical background drift. The reflective images of two targets, a Nikon camera’s lens cap and a plastic toy gun, are obtained. For the lens cap, the image data were processed to be false-color images. For the toy gun, we show that even under an optically opaque canvas bag, a clear terahertz image is obtained. It is shown that terahertz real-time imaging can be used to nondestructively detect concealed objects.
    Optics Communications 01/2008; 281(6):1473-1475. · 1.44 Impact Factor
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    ABSTRACT: Terahertz (THz) radiation, which occupies a relatively unexplored portion of the electromagnetic spectrum between the mid-infrared and microwave bands, offers innovative sensing and imaging technologies that can provide information unavailable through conventional methods such as microwave and X-ray techniques. With the advancement of THz technologies, THz sensing and imaging will impact a broad range of interdisciplinary fields, including chemical and biological detections and identifications. In particular, THz radiation offers the opportunity for transformational advances in defense and security. Recent work shows that THz technologies are promising for the standoff detection and identification of explosive targets.
    Proceedings of the IEEE 09/2007; · 6.91 Impact Factor
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    Proceedings of the IEEE. 01/2007; 95(8).
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    Hua Zhong, Nick Karpowicz, X.-C. Zhang
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    ABSTRACT: We report the characterization of the emission profile of terahertz waves generated by four-wave mixing in the presence of laser-induced plasma. Highly directional terahertz waves with a divergence angle smaller than 10° are measured in the presence of long plasmas (>10 mm). Frequency-dependent interference structures in the angular distribution of the radiation are observed under tighter focusing conditions and are explained by intense self-phase modulation of the optical pulse in the plasma. This study reveals that terahertz generation from four-wave mixing in air plasmas is a promising source for spectroscopy and imaging in the terahertz range.
    Applied Physics Letters 06/2006; 88(26):261103-261103-3. · 3.79 Impact Factor
  • H. Zhong, N. Karpowicz, X.-C. Zhang
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    ABSTRACT: Terahertz (THz) waves generated through four-wave mixing in laser-induced air plasmas are an ideal source for imaging arbitrary locations. Under an amplified laser beam, ionized ambient air as a mixing medium provides broadband pulses with an unprecedented THz electric field strength among all the optically induced THz waves from nonlinear materials. We report the use of plasma-induced THz waves for 2D imaging for the first time, and compare it to other methods.
    01/2006;
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    ABSTRACT: Terahertz (THz) radiation, which occupies a large portion of the electromagnetic spectrum between the mid-infrared and microwave bands, offers innovative imaging and sensing technologies that can provide information, which may not be available through conventional methods (i.e. microwave and X-ray techniques.) As THz wave (T-ray) technology improves, we believe new THz wave sensing and imaging capabilities will impact a range of interdisciplinary fields, including: communications, imaging, medical diagnosis, health monitoring, environmental control, and chemical and biological identification. This is particularly crucial for identifying terrorist threats in homeland security (three to five years), and medical diagnosis or even clinical treatment in biomedical applications (five to ten years).
    Microwave Photonics, 2005. MWP 2005. International Topical Meeting on; 11/2005
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    ABSTRACT: We present recent progress in the use of continuous wave THz imaging for nondestructive testing applications. We present results demonstrating the use of hyperbolic lenses to achieve diffraction-limited resolution in a CW system and show applications of the technology while discussing its strengths and limitations.
    Infrared and Millimeter Waves and 13th International Conference on Terahertz Electronics, 2005. IRMMW-THz 2005. The Joint 30th International Conference on; 10/2005
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    ABSTRACT: We report on the detection of space shuttle foam insulation defects with a 0.2 THz Gunn diode oscillator as the illumination source. A pyroelectric camera, a Golay cell, and a silicon beam lead diode are used as detectors. The size and location of the defects are identified and the feasibility of using this imaging system in quality inspection is discussed.
    Infrared and Millimeter Waves, 2004 and 12th International Conference on Terahertz Electronics, 2004. Conference Digest of the 2004 Joint 29th International Conference on; 11/2004
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    ABSTRACT: We report detection of space shuttle insulation foam defects by using a 0.2 THz Gunn diode oscillator as the light source, and a pyroelectric camera as the detector. The size and location of the defects are identified, and the feasibility of using this imaging system in quality inspection is discussed.
    10/2004;
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    ABSTRACT: Pulsed THz imaging is a promising non-destructive technology based on its high transmission through selected dielectric materials and its capability to provide time-of-flight and spectral information. The traditional method of the pulsed THz imaging is a point-to-point reflective scanning system. The image is acquired by analyzing the peak amplitude information of the THz pulse in the time-domain at each pixel. It requires the THz beam or sample scanned. In this paper, we present our approach of large scale, focal plane THz wave imaging. In our 2-D focal plane THz wave imaging, the THz beam is expanded to be 60 mm in diameter. The THz beam illuminates the target in a reflective manner, in which a polyethylene lens projects the image onto a 40 mm by 40 mm by 2 mm ZnTe sensor crystal. The probe beam is expanded to be 40 mm in diameter and overlap with the THz beam on the sensor. The modulated probe beam profile carrying the image information is captured by a CCD camera. This technique enables us to view the objects which are optically opaque but transparent in THz frequency and shows feasibility in remote sensing, security inspection, and military defense applications.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
    09/2004;
  • [show abstract] [hide abstract]
    ABSTRACT: Pulsed THz imaging is a promising non-destructive technology based on its high transmission through selected dielectric materials and its capability to provide time-of-flight and spectral information. The traditional method of the pulsed THz imaging is a point-to-point reflective scanning system. The image is acquired by analyzing the peak amplitude information of the THz pulse in the time-domain at each pixel. It requires the THz beam or sample scanned. In this paper, we present our approach of large scale, focal plane THz wave imaging. In our 2-D focal plane THz wave imaging, the THz beam is expanded to be 60 mm in diameter. The THz beam illuminates the target in a reflective manner, in which a polyethylene lens projects the image onto a 40 mm by 40 mm by 2 mm ZnTe sensor crystal. The probe beam is expanded to be 40 mm in diameter and overlap with the THz beam on the sensor. The modulated probe beam profile carrying the image information is captured by a CCD camera. This technique enables us to view the objects which are optically opaque but transparent in THz frequency and shows feasibility in remote sensing, security inspection, and military defense applications.
    Proc SPIE 01/2004;