Achieving a high-quality (Q) factor for microresonators at a longer wavelength, e.g. longwave infrared (LWIR) with a wavelength from 8 to 14 um, will trigger new development in integrated non-linear optics and sensing on a chip. Although there are both powerful integrated light sources like solid-state quantum cascade lasers (QCLs) and strong driving force from chip-based sensing applications in the LWIR atmospheric transparent window, the Q factors of the microresonators are only several thousand, due to limited choices of low-loss materials and complicated fabrication procedures. Here, we report on the realization of a germanium (Ge) whispering gallery mode microresonator from a facile non-epitaxy fabrication process of high-quality Ge material with an ultra-smooth surface. By coupling the output of a QCL at 7.8 um into a partially suspended Ge on glass waveguide, an intrinsic Q of 2.5 ×105 are reported. Compared with the previous study, our work shows the importance and great promise of maintaining high-quality material for integrated photonics at LWIR.
A powerful class of techniques utilizing frequency combs is that of multiheterodyne techniques. These techniques use each individual, evenly space, spectral line of a comb as a local oscillator to measure a source's spectrum. By mixing an unknown source with that of a comb one can convert an optical signal into an electrical signal where standard radio-frequency (RF) electronics can be used. However, these techniques have been limited to measuring coherent sources, such as lasers, due to their inability to disambiguate signals that overlap in the down-converted intermediate frequencies (IF). This excludes most natural sources from being measured. In this manuscript, we present a new dual-comb technique that allows for the measurement of any arbitrary spectrum, even incoherent ones that span multiple comb lines.1, 2 It is shown that using the same equipment required in a dual-comb experiment one can calculate a correlation function between the two channels that has all the information required for accurate reconstruction. We brie y present the theory followed by simulation and an RF comb experiment.
We propose and demonstrate a novel multiphoton frequency-domain fluorescence lifetime imaging microscopy (MPM-FD-FLIM) system that is able to generate 3D lifetime images in deep scattering tissues. The imaging speed of FD-FLIM is improved using phase multiplexing, where the fluorescence signal is split and mixed with the reference signal from the laser in a multiplexing manner. The system allows for easy generation of phasor plots, which not only address multi-exponential decay problems but also clearly represent the dynamics of the fluorophores being investigated. Lastly, a sensorless adaptive optics setup is used for FLIM imaging in deep scattering tissues. The capability of the system is demonstrated in fixed and living animal models, including mice and zebrafish.
We present the first experimental demonstration of super-resolution multiphoton frequency-domain (FD) fluorescence lifetime imaging microscopy (FLIM). This is obtained through a novel microscopy technique called generalized stepwise optical saturation (GSOS). GSOS√utilizes the linear combination of M steps of raw images to improve the imaging resolution by a factor of √M . Here, a super-resolution multiphoton FD-FLIM is demonstrated on various samples, including fixed cells and biological tissues, with a custom-built two-photon FD-FLIM microscope. We demonstrate simultaneous super-resolution intensity and fluorescence lifetime images of a variety of cell cultures and ex vivo tissues. Combined with multiphoton excitation, the proposed GSOS microscopy is able to generate super-resolution FLIM images deep in scattering samples.
In this report the development of a low SWAP-C mid-infrared imaging system is outlined. This system is designed with a commercially available Vanadium-oxide (VOx) microbolometer camera costing $250 controlled via a Raspberry Pi (RPi) and Python. The camera used was previously characterized to have a NEDT of 25 mK for an integration time of 3.43s at 7 Hz framerate, but from software modifications discussed in this paper it was found that the cameras framerate can be pushed to 32 Hz lowering this integration time to 0.75 s. Due to the low SWAP-C characteristics of the design and the plug-and-play nature of the camera paired with Python code, this system can enable MIR imaging applications that are currently limited by the SWAPC characteristics of currently available detection systems. After outlining the development of interfacing the camera with a computer/microcontroller, the cameras code is extended to a client-server operation that allows for wireless control of the imaging system. This further enables remote operation for applications such as dronebased monitoring/surveillance or trace explosives detection. The report concludes with the discussion of two potential applications of distributed imaging and spectroscopic organics detection.
Many long-wave infrared spectroscopic imaging applications are limited by the portability and cost of detector arrays. We present a characterization of a newly available, low-cost, uncooled vanadium oxide microbolometer array, the Seek Compact, in accordance with common infrared detector specifications: noise-equivalent differential temperature (NEDT), optical responsivity spectra, and Allan variance. The Compact’s imaging array consists of 156×206 pixels with a 12-μm pixel pitch, 93% of the pixels yield useful temperature readings. Characterization results show optical response between λ=7.4 and 12 μm with an NEDT of 148 mK (at ≈7 fps). Comparing these results to a research-grade camera, the Seek Compact exhibits a 4× and 48× reduction in weight (2.0/0.5 lbs) and cost ($12,000/$250) but takes 93× longer to achieve the same NEDT (1.55 s/16.6 ms for 45 mK). Additionally, a proof-of-concept spectral imaging experiment of SiN thin films is conducted. Leveraging this price reduction and spectroscopic imaging capability, the Seek Compact has potential in enabling field-deployable and distributed active midinfrared spectroscopic imaging, where cost and portability are the dominate inhibitors and high frame rates are not required.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.