Abstract-Permanently reconfigured metamaterials due to terahertz induced mass transfer of gold

Permanently reconfigured metamaterials due to terahertz induced mass transfer of gold Andrew C. Strikwerda, Maksim Zalkovskij, Krzysztof Iwaszczuk, Dennis Lund Lorenzen, and Peter Uhd Jepsen  »View Author Affiliations

Optics Express, Vol. 23, Issue 9, pp. 11586-11599 (2015)
http://dx.doi.org/10.1364/OE.23.011586

http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-23-9-11586

View Full Text Article

Enhanced HTML    Acrobat PDF (4111 KB)

Abstract

We present a new technique for permanent metamaterial reconfiguration via optically induced mass transfer of gold. This mass transfer, which can be explained by field-emission induced electromigration, causes a geometric change in the metamaterial sample. Since a metamaterial’s electromagnetic response is dictated by its geometry, this structural change massively alters the metamaterial’s behavior. We show this by optically forming a conducting pathway between two closely spaced dipole antennas, thereby changing the resonance frequency by a factor of two. After discussing the physics of the process, we conclude by presenting an optical fuse that can be used as a sacrificial element to protect sensitive components, demonstrating the applicability of optically induced mass transfer for device design.

© 2015 Optical Society of America

Abstract-Nitrogen plasma formation through terahertz-induced ultrafast electron field emission

Nitrogen plasma formation through terahertz-induced ultrafast electron field emission Krzysztof Iwaszczuk, Maksim Zalkovskij, Andrew C. Strikwerda, and Peter U. Jepsen  »View Author Affiliations

http://www.opticsinfobase.org/optica/abstract.cfm?uri=optica-2-2-116

Optica, Vol. 2, Issue 2, pp. 116-123 (2015)
http://dx.doi.org/10.1364/OPTICA.2.000116

View Full Text Article

Enhanced HTML    Acrobat PDF (18

Electron microscopy and electron diffraction techniques rely on electron sources. Those sources require strong electric fields to extract electrons from metals, either by the photoelectric effect, driven by multiphoton absorption of strong laser fields, or in the static field emission regime. Terahertz (THz) radiation, commonly understood to be nonionizing due to its low photon energy, is here shown to produce electron field emission. We demonstrate that a carrier-envelope phase-stable single-cycle optical field at THz frequencies interacting with a metallic microantenna can generate and accelerate ultrashort and ultrabright electron bunches into free space, and we use these electrons to excite and ionize ambient nitrogen molecules near the antenna. The associated UV emission from the gas forms a novel THz wave detector, which, in contrast with conventional photon-counting or heat-sensitive devices, is ungated and sensitive to the peak electric field in a strongly nonlinear fashion.

© 2015 Optical Society of America

Abstract-Structural Control of Metamaterial Oscillator Strength and Electric Field Enhancement at Terahertz Frequencies

George R. Keiser, Huseyin R. Seren, Andrew C. Strikwerda, Xin Zhang, Richard D. Averitt

(Submitted on 4 Jun 2014)

The design of artificial nonlinear materials requires control over the internal resonant charge densities and local electric field distributions. We present a MM design with a structurally controllable oscillator strength and local electric field enhancement at terahertz frequencies. The MM consists of a split ring resonator (SRR) array stacked above an array of nonresonant closed conducting rings. An in-plane, lateral shift of a half unit cell between the SRR and closed ring arrays results in a decrease of the MM oscillator strength by a factor of 4 and a 40% change in the amplitude of the resonant electric field enhancement in the SRR capacitive gap. We use terahertz time-domain spectroscopy and numerical simulations to confirm our results and we propose a qualitative inductive coupling model to explain the observed electromagnetic reponse.

Abstract-Metamaterial composite bandpass filter with an ultra-broadband rejection bandwidth of up to 240 terahertz

Andrew C. Strikwerda^1,a), Maksim Zalkovskij¹, Dennis Lund Lorenzen¹,

Alexander Krabbe¹, Andrei V. Lavrinenko¹ and Peter Uhd Jepsen¹


1 DTU Fotonik—Department of Photonics Engineering, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark
a) Author to whom correspondence should be addressed. Electronic mail: astr@fotonik.dtu.dk.
Appl. Phys. Lett. 104, 191103 (2014); http://dx.doi.org/10.1063/1.4875795

http://scitation.aip.org/content/aip/journal/apl/104/19/10.1063/1.4875795

We present a metamaterial, consisting of a cross structure and a metal mesh filter, that forms a composite with greater functional bandwidth than any terahertz (THz) metamaterial to date.Metamaterials traditionally have a narrow usable bandwidth that is much smaller than commonTHz sources, such as photoconductive antennas and difference frequency generation. The composite structure shown here expands the usable bandwidth to exceed that of current THz sources. To highlight the applicability of this combination, we demonstrate a series ofbandpass filters with only a single pass band, with a central frequency (f0 ) that is scalable from 0.86–8.51 THz, that highly extinguishes other frequencies up to >240 THz. The performance of these filters is demonstrated in experiment, using both air biased coherent detection and a Fourier transform infrared spectrometer (FTIR), as well as in simulation. We present equations—and discuss their scaling laws—which detail the f0 and full width at half max (Δf) of the pass band, as well as the required geometric dimensions for their fabrication using standard UVphotolithography and easily achievable fabrication linewidths. With these equations, the geometric parameters and Δf for a desired frequency can be quickly calculated. Using thesebandpass filters as a proof of principle, we believe that this metamaterial composite provides the key for ultra-broadband metamaterial design.

Abstract-Experimental three-dimensional beam profiling and modeling of a terahertz beam generated from a two-color air plasma

Pernille Klarskov¹, Andrew C Strikwerda, Krzysztof Iwaszczuk and Peter Uhd Jepsen
Hide affiliations

pkpe@fotonik.dtu.dk
DTU Fotonik—Department of Photonics Engineering, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark
¹ Author to whom any correspondence should be addressed. 

http://m.iopscience.iop.org/1367-2630/15/7/0

We use a broadband microbolometer array to measure the full three-dimensional (3D) terahertz (THz) intensity profile emitted from a two-color femtosecond plasma and subsequently focused in a geometry useful for nonlinear spectroscopic investigations. Away from the immediate focal region we observe a sharp, conical intensity profile resembling a donut, and in the focal region the beam collapses to a central, Lorentz-shaped profile. The Lorentzian intensity profile in the focal region can be explained by considering the frequency-dependent spot size derived from measurements of the Gouy phase shift in the focal region, and the transition from the donut profile to a central peak is consistent with propagation of a Bessel–Gauss beam, as shown by simulations based on a recent transient photocurrent model (You et al 2012 Phys. Rev. Lett. 109 183902). We combine our measurements to the first full 3D visualization of the conical THz emission from the two-color plasma.

GENERAL SCIENTIFIC SUMMARY 
Introduction and background. Nonlinear spectroscopy with intense terahertz (THz) light is an important tool for the understanding of anharmonicities and couplings in low-energy interactions in solids, liquids and gases. The light intensity is one of the key parameters in any nonlinear experiment. It is determined by the detailed shape of the beam in time and space. An intense femtosecond laser beam focused with its second harmonic in air forms a plasma which generates ultrashort THz pulses with high bandwidth and intensity. The THz radiation emitted from such air plasmas has intriguing propagation properties that we explore here.
Main results. We measure the full three-dimensional (3D) THz intensity profile emitted from a two-color femtosecond plasma and subsequently focused in a geometry useful for nonlinear spectroscopic investigations. Away from the immediate focal region we observe a sharp, conical intensity profile resembling a donut, and in the focal region the beam collapses to a central, Lorentz-shaped profile. This Lorentzian beam shape is due to weighted superposition of the Gaussian beam profiles at the individual frequencies within the bandwidth of the THz beam. We demonstrate that the transition from the donut profile to a central peak is consistent with propagation of a Bessel–Gauss beam.
Wider implications. The femtosecond two-color air plasma THz source has appealing properties such as ultrabroad frequency contents, ultrashort transform-limited pulse duration, and high peak field strength, three important properties for ultrafast, nonlinear spectroscopy. The focusing properties investigated here must be carefully considered when designing nonlinear or pump-probe experiments.

Figure. A donut-shaped THz beam profile emitted from a femtosecond two-color plasma is focused to a central spot due to its Bessel–Gauss propagation characteristics.

Abstract-Nonlinear Terahertz Metamaterials via Field-Enhanced Carrier Dynamics in GaAs

Kebin Fan¹, Harold Y. Hwang², Mengkun Liu³, Andrew C. Strikwerda³, Aaron Sternbach³, Jingdi Zhang³, Xiaoguang Zhao¹, Xin Zhang¹, Keith A. Nelson², and Richard D. Averitt^3 
1Department of Mechanical Engineering, Boston University, 110 Cummington Street, Boston, Massachusetts 02215, USA
²Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

We demonstrate nonlinear metamaterial split ring resonators (SRRs) on GaAs at terahertz frequencies. For SRRs on doped GaAs films, incident terahertz radiation with peak fields of ∼20–160  kV/cm drives intervalley scattering. This reduces the carrier mobility and enhances the SRR LC response due to a conductivity decrease in the doped thin film. Above ∼160  kV/cm, electric field enhancement within the SRR gaps leads to efficient impact ionization, increasing the carrier density and the conductivity which, in turn, suppresses the SRR resonance. We demonstrate an increase of up to 10 orders of magnitude in the carrier density in the SRR gaps on semi-insulating GaAs. Furthermore, we show that the effective permittivity can be swept from negative to positive values with an increasing terahertz field strength in the impact ionization regime, enabling new possibilities for nonlinear metamaterials.

© 2013 American Physical Society

Abstract-Three-dimensional broadband tunable terahertz metamaterials

Kebin Fan, Andrew C. Strikwerda, Xin Zhang, and Richard D. Averitt
http://prb.aps.org/accepted/c107fO2eN53E431002bb4d976a7de3bdae23bd268
We present optically tunable magnetic 3D metamaterials at terahertz (THz) frequencies which exhibit a tuning range of ~ 30% of the resonance frequency. This is accomplished by fabricating 3D array structures consisting of double-split-ring resonators (DSRRs) on silicon-on-sapphire, fabricated using multilayer electroplating. Photoexcitation of free carriers in the silicon within the capacitive region of the DSRR results in a red-shift of the resonant frequency from 1.74 THz to 1.16 THz. The observed frequency shift leads to a transition from a magnetic-to-bianisotropic response as verified through electromagnetic simulations and parameter retrieval. Our approach extends dynamic metamaterial tuning to magnetic control, and may find applications in switching and modulation, polarization control, or tunable perfect absorbers.

Abstract-Three Dimensional Broadband Tunable Terahertz Metamaterials

http://arxiv.org/abs/1301.3977
Kebin Fan, Andrew C. Strikwerda, Xin Zhang, Richard D. Averitt

We present optically tunable magnetic 3D metamaterials at terahertz (THz) frequencies which exhibit a tuning range of ~30% of the resonance frequency. This is accomplished by fabricating 3D array structures consisting of double-split-ring resonators (DSRRs) on silicon-on-sapphire, fabricated using multilayer electroplating. Photoexcitation of free carriers in the silicon within the capacitive region of the DSRR results in a red-shift of the resonant frequency from 1.74 THz to 1.16 THz. The observed frequency shift leads to a transition from a magnetic-to-bianisotropic response as verified through electromagnetic simulations and parameter retrieval. Our approach extends dynamic metamaterial tuning to magnetic control, and may find applications in switching and modulation, polarization control, or tunable perfect absorbers.

Microwave and terahertz wave sensing with metamaterials

MY NOTE: MORE ON USE OF METAMATERIAL FOR THz, GENERATION

http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-19-22-21620

Abstract

We have designed, fabricated, and characterized metamaterial enhanced bimaterial cantilever pixels for far-infrared detection. Local heating due to absorption from split ring resonators (SRRs) incorporated directly onto the cantilever pixels leads to mechanical deflection which is readily detected with visible light. Highly responsive pixels have been fabricated for detection at 95 GHz and 693 GHz, demonstrating the frequency agility of our technique. We have obtained single pixel responsivities as high as 16,500 V/W and noise equivalent powers of 10⁻⁸ W/Hz^1/2 with these first-generation devices.

© 2011 OSA

» View Full Text: Acrobat PDF (2403 KB)