John Kohoutek

Opto-mechanical force mapping of deep subwavelength plasmonic modes.

We present spatial mapping of optical force generated near the hot spot of a metal-dielectric-metal bowtie nanoantenna at a wavelength of 1550 nm. Maxwells stress tensor method has been used to simulate the optical force and it agrees well with the experimental data. This method could potentially produce field intensity and optical force mapping simultaneously with a high spatial resolution. Detailed mapping of the optical force is crucial for understanding and designing plasmonic-based optical trapping for emerging applications such as chip-scale biosensing and optomechanical switching.

Quantum-cascade laser integrated with a metal–dielectric–metal-based plasmonic antenna

Optical nanoantennas are capable of enhancing the near-field intensity and confining optical energy within a small spot size. We report a novel metal-dielectric-metal coupled-nanorods antenna integrated on the facet of a quantum-cascade laser. Finite-difference time-domain simulations showed that, for dielectric thicknesses in the range from 10 to 30 nm, peak optical intensity at the top of the antenna gap is 4000 times greater than the incident field intensity. This is 4 times higher enhancement compared to a coupled metal antenna. The antenna is fabricated using focused ion-beam milling and measured using modified scanning probe microscopy. Such a device has potential applications in building mid-IR biosensors.

Composite Nano-Antenna Integrated With Quantum Cascade Laser

Exploiting optical nano-antennas to boost the near-field confinement within a small volume can increase the limit of molecular detection by an order of magnitude. We present a novel antenna design based on Au-SiO2-Au single nanorod integrated on the facet of a quantum cascade laser operating in the midinfrared region of the optical spectrum. Finite-difference time-domain simulations showed that for sandwiched dielectric thicknesses within the range of 20-30 nm, peak optical intensity at the top of the antenna ends is 500 times greater than the incident field intensity. The device was fabricated using focused ion beam milling. Apertureless midinfrared near-field scanning optical microscopy showed that the device can generate a spatially confined spot within a nanometric size about 12 times smaller than the operating wavelength. Such high intensity, hot spot locations can be used in increasing photon interaction with bio-molecules for sensing applications.

Integrated all-optical infrared switchable plasmonic quantum cascade laser.

We report a type of infrared switchable plasmonic quantum cascade laser, in which far field light in the midwave infrared (MWIR, 6.1 μm) is modulated by a near field interaction of light in the telecommunications wavelength (1.55 μm). To achieve this all-optical switch, we used cross-polarized bowtie antennas and a centrally located germanium nanoslab. The bowtie antenna squeezes the short wavelength light into the gap region, where the germanium is placed. The perturbation of refractive index of the germanium due to the free carrier absorption produced by short wavelength light changes the optical response of the antenna and the entire laser intensity at 6.1 μm significantly. This device shows a viable method to modulate the far field of a laser through a near field interaction.

Signal-to-noise performance of a short-wave infrared nanoinjection imager

We report on the signal-to-noise performance of a nanoinjection imager, which is based on a short-wave IR InGaAs/GaAsSb/InP detector with an internal avalanche-free amplification mechanism. Test pixels in the imager show responsivity values reaching 250 A/W at 1550 nm, -75 degrees C, and 1.5V due to an internal charge amplification mechanism in the detector. In the imager, the measured imager noise was 28 electrons (e(-)) rms at a frame rate of 1950 frames/s. Additionally, compared to a high-end short-wave IR imager, the nanoinjection camera shows 2 orders of magnitude improved signal-to-noise ratio at thermoelectric cooling temperatures primarily due to the small excess noise at high amplification.

A Short-Wave Infrared Nanoinjection Imager With 2500 A/W Responsivity and Low Excess Noise

We report on a novel nanoinjection-based short-wave infrared imager, which consists of InGaAs/GaAsSb/InAlAs/InP-based nanoinjection detectors with internal gain. The imager is 320×256 pixels with a 30-m pixel pitch. The test pixels show responsivity values in excess of 2500 A/W, indicating generation of more than 2000 electrons/photon with high quantum efficiency. This amplification is achieved at complementary metal-oxide semiconductor (CMOS) compatible, subvolt bias. The measured excess noise factor F of the hybridized imager pixels is around 1.5 at the responsivity range 1500 to 2000 A/W. The temperature behavior of the internal dark current of the imager pixels is also studied from 300 to 77 K. The presented results show, for the first time, that the nanoinjection mechanism can be implemented in imagers to provide detector-level internal amplification, while maintaining low noise levels and CMOS compatibility.

An opto-electro-mechanical infrared photon detector with high internal gain at room temperature.

Many applications require detectors with both high sensitivity and linearity, such as low light level imaging and quantum computing. Here we present an opto-electro-mechanical detector based on nano-injection and lateral charge compression that operates at the short infrared (SWIR) range. Electrical signal is generated by photo-induced changes in a nano-injector gap, and subsequent change of tunneling current. We present a theoretical model developed for the OEM detector, and it shows good agreement with the measured experimental results for both the mechanical and electrical properties of the device. The device shows a measured responsivity of 276 A/W, equivalent to 220 electrons per incoming photon, and an NEP of 3.53 x 10(-14) W/Hz(0.5) at room temperature. Although these results are already competing with common APDs in linear mode, we believe replacing the AFM tip with a dedicated nano-injector can improve the sensitivity significantly.

Towards an Integrated Chip-Scale Plasmonic Biosensor

Biosensing allows researchers to detect tiny amounts of harmful chemicals before they become major threats. These researchers are using advanced optical technologies to develop the biosensor of the future-a plasmonic-based chip-scale device that will allow for compact, inexpensive, ubiquitous and sensitive detection.

Dynamic measurement and modeling of the Casimir force at the nanometer scale

We present a dynamic method for measurement of the Casimir force with an atomic force microscope (AFM) with a conventional AFM tip. With this method, originally based on the phase of vibration of the AFM tip, we are able to verify the Casimir force at distances of nearly 6 nm with an AFM tip that has a radius of curvature of nearly 100 nm. Until now dynamic methods have been done using large metal spheres at greater distances. Also presented is a theoretical model based on the harmonic oscillator, including nonidealities. This model accurately predicts the experimental data.

An apertureless near-field scanning optical microscope for imaging surface plasmons in the mid-wave infrared

An apertureless near-field scanning optical microscope (a-NSOM) setup is described. Special consideration is given to important system components. Surface plasmons are defined, as is their relationship to a- NSOM and their interaction with the scanning probe tip. We used this set-up to measure a metal-dielectric-metal (MDM) antenna integrated with a quantum cascade laser (QCL). The former is introduced and described. The role of the atomic force microscope (AFM) in the experiment is laid out and explained. Finally, the lock-in amplifier is explained. Next, the system setup is introduced and explained from the point of view of the light path taken by light generated in the laser. Finally, results are given for the MDM single nanorod antenna and the coupled MDM nanorod antenna. Simulation, topography, and NSOM images are shown. Lastly, several experimental issues are discussed as well as other types of NSOM.