Mid-infrared near-field superlenses to overcome the diffraction limit
CIC nanoGUNE Seminars
- Speaker
-
Peining Li, . Physikalisches Institut (IA) IR-Nano-Group RWTH Aachen University (Germany)
- When
-
2015/10/02
13:00 - Place
- nanoGUNE seminar room, Tolosa Hiribidea 76, Donostia - San Sebastian
- Add to calendar
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New metamaterial-based imaging concepts such as perfect lenses [1],
superlenses [2,3] and hyperlenses [4] offer great possibilities to realize
sub-diffraction-limited optical imaging. However, most of these achievements
have focused on the visible wavelength. In this talk we present and discuss
the development of infrared-version superlenses (hyperlenses) that could be
used for future infrared microscopy and spectroscopy.
We provide an experimental study of the basic imaging mechanism of an infrared
silicon carbide (SiC) superlens. We have experimentally mapped the dispersion
relation of a 500-nm-thick SiC superlens through the real-space imaging of the
launched surface phonon polariton modes. The obtained dispersion map clearly
reveals that the so-called ‘superlensing’ effect (subdiffractive imaging
using the superlens) originates from the evanescent-field enhancement enabled
by the surface polariton modes.
However, the SiC superlens is not suitable for broadband applications owing to
a very narrow wavelength bandwidth. In order to overcome this limitation, we
have also proposed a wavelength-tunable graphene lens that can work at
different wavelengths [5]. This graphene lens due to its non-resonant
enhancement of evanescent fields yields new promising properties including
broad intrinsic bandwidth and low sensitivity to loss, together with a still
good subwavelength resolution of around λ/7 for a two-layer case and over
λ/10 for the multilayered configuration. Most importantly, the working
wavelength of the graphene lens can be electrically tuned via the dynamical
tuning of the graphene conductivity. This large tunability allows it to cover
a very broad infrared wavelength range. As a proof of this theory concept, we
have also experimentally demonstrated that a monolayer-graphene lens offers a
7-fold enhancement of evanescent information, improving conventional infrared
near-field microscopy to resolve buried structures at a 500-nm depth with
λ/11-resolution [6].
Moreover, we have also investigated the near-field imaging through a natural
hyperbolic material, hexagonal boron nitride (hBN).[7] We have demonstrated
that a thin, flat hBN slab exhibits wavelength-dependent multifunctional
imaging operations, offering both the superlensing of single objects with down
to λ/32 resolution, as well as enabling an enlarged imaging of the outline of
the object. Both imaging functionalities can be explained based on the volume-
confined, wavelength dependent propagation angle of hyperbolic phonon
polaritons in hBN.
Our results provide in-depth physical understanding and experimental proofs of
different infrared superlenses and will inspire future superlens-based high-
resolution infrared microscopy and spectroscopic applications.
1\. J. B. Pendry, “Negative refraction makes a perfect lens,†Physical
Review Letters, 85, 3966 (2000).
2\. N. Fang, H. Lee, C. Sun, and X. Zhang, “Sub–diffraction-limited
optical imaging with a silver superlens,†Science, 308, 534–537 (2005).
3\. T. Taubner, D. Korobkin, Y. Urzhumov, G. Shvets, and R. Hillenbrand,
“Near-field microscopy through a sic superlens,†Science, 313, 1595
(2006).
4\. Z. Liu, H. Lee, Y. Xiong, C. Sun, and X. Zhang, “Far-field optical
hyperlens magnifying sub-diffraction-limited objects†Science, 315, 1686
(2007).
5\. P. Li and T. Taubner, “Broadband subwavelength imaging using a tunable
graphene-lensâ€. ACS nano 6, 10107 (2012).
6\. P. Li, T. Wang, H. Boeckmann, and T. Taubner, “Graphene-Enhanced
Infrared Near-Field Microscopy†Nano Lett. 4, 4400 (2014)
7\. P. Li, et al., “Hyperbolic phonon-polaritons in boron bitride for near-
field optical imaging and focusingâ€. Nature communications 6, 7507 (2015).
**Host** : Rainer Hillenbrand