Browsing by Subject "Photodetection"

Active plasmonic nanostructures with tunable resonances promise to enable smart materials with multiple functionalities, on-chip spectral-based imaging and low-power optoelectronic devices. A variety of tunable materials have been integrated with plasmonic structures, however, the tuning range in the visible regime has been limited and small on/off ratios are typical for dynamically switchable devices. An all optical tuning mechanism is desirable for on-chip optical computing applications. Furthermore, plasmonic structures are traditionally fabricated on rigid substrates, restricting their application in novel environments such as in wearable technology.

In this dissertation, I explore the mechanisms behind dynamic tuning of plasmon resonances, as well as demonstrate all-optical tuning through multiple cycles by incorporating photochromic molecules into plasmonic nanopatch antennas. Exposure to ultraviolet (UV) light switches the molecules into a photoactive state enabling dynamic control with on/off ratios up to 9.2 dB and a tuning figure of merit up to 1.43, defined as the ratio between the spectral shift and the initial line width of the plasmonic resonance. Moreover, the physical mechanisms underlying the large spectral shifts are elucidated by studying over 40 individual nanoantennas with fundamental resonances from 550 to 720 nm revealing good agreement with finite-element simulations.

To fully explore the tuning capabilities, the molecules are incorporated into plasmonic metasurface absorbers based on the same geometry as the single nanoantennas. The increased interaction between film-coupled nanocubes and resonant dipoles in the photochromic molecules gives rise to strong coupling. The coupling strength can be quantified by the Rabi-splitting of the plasmon resonance at ~300 meV, well into the ultrastrong coupling regime.

Additionally, fluorescent emitters are incorporated into the tunable absorber platform to give dynamic control over their emission intensity. I use optical spectroscopy to investigate the capabilities of tunable plasmonic nanocavities coupled to dipolar photochromic molecules. By incorporating emission sources, active control over the peak photoluminescence (PL) wavelength and emission intensity is demonstrated with PL spectroscopy.

Beyond wavelength tuning of the plasmon resonance, design and characterization is performed towards the development of a pyroelectric photodetector that can be implemented on a flexible substrate, giving it the ability to be conformed to new shapes on demand. Photodetection in the NIR with responsivities up to 500 mV/W is demonstrated. A detailed plan is given for the next steps required to fully realize visible to short-wave infrared (SWIR) pyroelectric photodetection with a cost-effective, scalable fabrication process. This, in addition to real-time control over the plasmon resonance, opens new application spaces for photonic devices that integrate plasmonic nanoparticles and actively tunable materials.

Thermal photodetectors are uniquely capable of sensing any incident wavelength and are only limited by the wavelength range of the integrated absorber, yet these detectors are commonly thought to be less sensitive and slower than their photoconductor (PC) or photovoltaic (PV) counterparts. As such, the use of thermal detectors for multispectral imaging has largely been ignored for spectral regions outside of the LWIR. However, recent theoretical and experimental developments have shown that thermal detectors with spectrally selective absorbers can outperform ideal PC and PV detectors in the MWIR and beyond. In this dissertation, thermal detectors integrated with spectrally selective, metasurface absorbers are theoretically and experimentally investigated. Large-area metasurface absorbers with resonances spanning from 340 to 2740 nm are developed that localize absorption and subsequent thermal generation in significantly subwavelength volumes. When integrated with a thermally sensitive pyroelectric film, the metasurface-pyroelectric detectors exhibit a sub-nanosecond response time with potential to match the response times of state-of-the-art, high-speed photodiodes. Overall, the spectrally selective thermal detectors developed here are a promising approach capable of disrupting the low cost, low form-factor spectral imaging market and providing an interesting platform to conduct research into photothermal generation and thermal diffusion at the nanoscale.