Quantum ghost imaging can be an important tool in making optical measurements. One of the most useful aspects of ghost imaging is the unique ability to correlate two sets of independently collected information. We aim to use the principles of ghost imaging to build out a 3-dimensional microscope which utilizes detection from two imaging detectors that simultaneously capture entangled light. Further advancements and application of this relatively new imaging method depends on understanding the limits of the optical system. What quality should we expect? Can we image out-of-focus objects? How long do we need to expose? For ghost imaging, these answers are not so obvious. This is because entangled light sources are atypical: the light profile, frequency distribution, and intensity, for instance, all depend on an assortment of parameters associated with how the entangled light was generated. While we cannot practically explore the extent of this configuration space, we present here an exploration of a very accessible range. We show in which ways a commonly used bulk non-linear crystal can alter the imaging capabilities. In this study, we utilize a pair of state-of-the-art, single-photon avalanche diode (SPAD) array detectors. Thus, we also use this study as an opportunity to demonstrate the capabilities of these detectors in their use for ghost imaging applications.
Fluorescence microscopy has become integral to biological studies for the technique’s ability to elucidate structures of biomolecules for in-situ studies with high selectivity and specificity. Imaging of intrinsic indicators, such as fluorescent amino acids in proteins, provides important information, but can be challenging to accomplish. Current microscopy techniques that measure native fluorescence without the use of exogenous labels involve either direct UV excitation which is commonly non-localized and can be detrimental to the system, or multiphoton absorption which must be conducted at high intensities, therefore posing high risks of photodamage. As such, we seek to investigate an efficient way to gently excite native fluorescence in biological systems in a way that overcomes these limitations. Quantum entangled photon pairs generated via spontaneous parametric downconversion (SPDC), may be an alternative to conducting two-photon absorption (TPA) to excite fluorescence in amino acids without the high fluences currently used. These photon pairs are highly correlated in time. Thus, the arrival of one photon is simultaneously followed by the arrival of its sister photon. As a result, a molecule interacting with the photon pair should simultaneously absorb both photons, leading to a linear two-photon absorption rate, and the linearity of the two-photon process should dramatically reduce the light intensity necessary for TPA. Therefore, quantum entangled photon pairs offer the possibility of performing low intensity UV excitation using photons in the visible wavelength range. With this work, we generated and characterized entangled photons generated via SPDC, and investigated whether fluorescent amino acids can be excited, and the subsequent fluorescence induced with entangled two-photon absorption. Results show that much higher entangled two-photon rates than what are currently available are needed to measure significant signals with entangled two-photon excitation.
The evolution of pathogens has increased the demand for a sensing and detection platform, capable of qualifying constituents in real time. Whispering Gallery Mode Resonators provide an ideal biochemical sensing platform due to their low cost, high sensitivity, and low impact on the analyte. These resonators have high quality factors and possess the ability to detect minute changes in the local environment, as the light traveling on the surface of the resonator, when at resonance interacts with the surrounding medium for interaction lengths on the order of ~10-100cm’s . These changes in physical properties are captured through shifts of the resonance wavelength, resonance dip intensity, and/or quality factor. In this work, we provide our design of a 3-D printed microfluidic cell that is compatible with our taper and sphere coupling scheme developed from our previous work. Initially, the baseline performance of the resonator fluidic system was established by measuring the resonance wavelength shift due to refractive index change from water to phosphate buffered saline (PBS). Next, we showcase our biofunctionalization procedure and measure the accumulation of pathogens, such as E. Coli and Influenza A, on the resonator’s surface. The presence of these biological analytes results in small changes in the resonator’s diameter and refractive index, which manifests in real time as a red shift of the resonance wavelength on the picometer scale. Finally, we develop the foundation for a silicon integrated circuit chip resonator system, resulting in a further reduction of our system’s footprint.
Shrinking the volumetric footprint of gas sensors is desirable as it allows for nonintrusive, nonperturbing gas mixture analysis and access to tight enclosures. Micro-resonators are a perfect candidate for these sensors as their size parameter (~micron) is minimal, and the typical surface propagating whispering gallery modes can interact with an analyte without disrupting the environment. The large, quality factor (Q) of these resonant cavity modes enables long interaction lengths on the order of 100s of centimeters between the optical field and analyte. Thus, the presence of a gas different than the nominal environment will result in a shift of the resonant properties, including the resonant wavelength, amplitude, and quality factor, that can be detected in real-time. To illustrate this effect, we utilized a spherical micro resonator on the end of a piece of optical fiber, formed using standard ball lens fabrication, and excited the resonant modes using a tapered optical fiber connected to tunable Infrared laser. The resonator was fixed in contact with the tapered region of fiber, and the assembly was placed inside an in-house, optically coupled, vacuum-tight vessel for gas testing. We compared the spectral response of air, pure CO2, and pure N2 gas, observing spectral shifting and broadening of the cavity resonances. In addition, the effect of vessel temperature on resonance peak position due to the thermo-optic effect was investigated and quantified. Lastly, a feedback arm was added to the setup to reduce signal noise and automated data analysis was implemented to improve data clarity.
We demonstrate an all-fiber super-continuum (SC) laser based near infrared (1160nm to 2350nm) spectroscopy system that is capable of measuring protein (gluten) levels in wheat flour, at a stand-off distance. We show that reflectance spectrum between 1160nm and 2350nm can be used to measure protein levels in wheat flour. The measured protein concentration with the partial least square regression shows a good linear correlation (R square >0.95) to the protein level measured by the Dumas method with standard error variance down to 0.5 percent. Our system could be used for non-destructive, real-time determination of the protein level of wheat flour at a stand-off distance in industrial settings such as food factories or flour milling plants.
KEYWORDS: Absorption, Near infrared, Spectroscopy, High power lasers, Nondestructive evaluation, Near infrared spectroscopy, Laser applications, Standoff detection, Supercontinuum sources
We demonstrate infrared spectroscopy systems that are capable of predicting acrylamide level in powders of potato fries based on all-fiber high power supercontinuum (SC) lasers in both the short-wave and mid-wave infrared spectral range. Two SC lasers used in this study cover wavelength range of 670nm to 2500nm and 1600nm to 11000nm, respectively. We use the spectroscopy system to measure 32 French fry samples with different acrylamide concentrations calibrated by gas chromatography-mass spectroscopy (GCMS). Our predicted acrylamide concentrations show a good linear correlation to the measured acrylamide concentration obtained through GCMS, and the partial least square regression analysis shows standard error down to 145ppb. Based on our results, our system could provide a non-destructive alternative method for determining the acrylamide in food samples at a stand-off distance, which could be important for near-line or in-line quality control purposes.
All-fiber integrated super-continuum (SC) sources are described based on a platform architecture that can operate in the visible, near-infrared, short-wave infrared, mid-wave infrared and long-wave infrared, with demonstrated SC wavelengths ranging from 0.47 to 12 μm. Modulation instability initiated SC generation leads to a simple SC source with no moving parts and that uses o_-the-shelf components from the mature telecommunications and fiber optics industry. The resulting light sources are basically a cascade of fibers pumped by fiber-pigtailed laser diodes and some drive and control electronics; thus, the SC sources have the potential to be cost-effective, compact, robust and reliable. Starting from fused silica fibers, the SC spectrum can be extended to shorter or longer wavelengths by cascading fibers with appropriate dispersion and/or transparency. As one example, we demonstrate a long-wave infrared SC source that generates a continuous spectrum from approximately 1.57 to 12 μm using a fiber cascade comprising fused silica fiber followed by ZBLAN fluoride fiber followed by sulfide fiber and, finally, a high-numerical-aperture selenide fiber. The time-averaged output power is as high as 417 mW at 33% duty cycle, and we observe a near-diffraction-limit, single spatial-mode beam across the entire spectral range. A prototype is described that is based on a three-layer architecture with a form factor of 16.7 × 10 × 5.7 and that plugs into a standard wall plug. This SC prototype has been used in a number of field tests as the active illuminator for stand-off FTIR system over distances of 5 to 25 m, thus enabling identification of targets or samples based on their chemical signature. Further optimization of the SC source will also be described to increase the output power and to reduce the form factor.
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