KEYWORDS: Holograms, Glasses, Digital holography, Contrast transfer function, High power microwaves, Chalcogenide glass, CCD cameras, Thin films, 3D image reconstruction, Optical engineering
Fingerprint analysis is a popular identification technique due to the uniqueness of fingerprints and the convenience of recording them. The quality of a latent fingerprint on a surface can depend on various conditions, such as the time of the day, temperature, and the composition of sweat. We first developed latent fingerprints on transparent and blackened glass slides by depositing 1000-nm-thick columnar thin films (CTFs) of chalcogenide glass of nominal composition Ge28Sb12Se60. Then, we used transmission-/reflection-mode multiwavelength digital holography to construct the topograms of CTF-developed fingerprints on transparent/blackened glass slides. The two wavelengths chosen were 514.5 and 457.9 nm, yielding a synthetic wavelength of 4.1624 μm, which is sufficient to resolve pores of depths 1 to 2 μm. Thus, our method can be used to measure the level-3 details that are usually difficult to observe with most other techniques applied to latent fingerprints.
Multiple surface-plasmon-polariton (SPP) waves are guided by the interface of a metal and a chiral sculptured thin film (STF) at a single wavelength. Spatially multiplexed 4-quadrant chips comprising a lanthanum-fluoride chiral STF embedded with a silver-nanoparticle layer were deposited atop an aluminum-coated glass substrate, each quadrant functioning as an autonomous sensor. The void regions of the chiral STF in each quadrant were in filtrated with sucrose solutions of increasing molarity and deployed in a prism-coupled surface-multi-plasmonics-resonance- imaging (SMPRI) machine. The angular locations of the SPP-wave modes shift as the molarity of the fluid increases, thus demonstrating simultaneous sensing of fluids via SMPRI.
Multiple surface-plasmon-polariton (SPP) waves at a single free-space wavelength can be guided by the interface of a metal and a chiral sculptured thin film (STF). Multilayers comprising a chiral STF of lanthanum fluoride deposited on an aluminum thin film deposited on a glass substrate were fabricated. In some chips, a 5-nm-thick layer of silver nanoparticles was deposited at one of two selected depths in the chiral STF. The chips were then deployed in a prism-coupled configuration in a custom-built machine for surface multiplasmonic resonance imaging (SMPRI), in order to observe the effects of the silver-nanoparticle layer on the multiple SPP-wave modes. The angular locations of the SPP-wave modes were found to be not greatly dependent on whether the silver-nanoparticle layer was deposited after the first or the second period of a three-periods-thick chiral STF. With aqueous solutions of sucrose as infiltrant fluids, the angular shifts of the SPP-wave modes were determined as the refractive index of the infiltrant fluid increased. The use of a charge-coupled devices camera and upgraded motion-control equipment for SMPRI was found to increase the sensitivity of the chip. The silver-nanoparticle layer was also found to enhance the sensitivity.
The analysis of fingerprints is important for biometric identification. Two-wavelength digital holographic
interferometry is used to study the topography of various types of fingerprints. This topography depends on
several conditions such as the temperature, time of the day, and the proportions of eccrine and sebaceous sweat.
With two-wavelength holographic interferometry, surface information can be measured with a better accuracy
compared to single-wavelength phase-retrieving techniques. Latent fingerprints on transparent glass, a
forensically relevant substrate are first developed by the deposition of 50–1000-nm-thick columnar thin films,
and then analyzed using the transmission-mode two-wavelength digital holographic technique. In this technique,
a tunable Argon-ion laser (457.9 nm to 514.5 nm) is used and holograms are recorded on a CCD camera
sequentially for several sets of two wavelengths. Then the phase is reconstructed for each wavelength, and the
phase difference which corresponds to the synthetic wavelength (4 μm to 48 μm) is calculated. Finally, the
topography is obtained by applying proper phase-unwrapping techniques to the phase difference. Interferometric
setups that utilize light reflected from the surface of interest have several disadvantages such as the effect of
multiple reflections as well as the effects of the tilt of the object and its shadow (for the Mach-Zehnder
configuration). To overcome these drawbacks, digital holograms of fingerprints in a transmission geometry are
used. An approximately in-line geometry employing a slightly tilted reference beam to facilitate separation of
various diffraction orders during holographic reconstruction is employed.
Experimentation with obliquely incident light established that all four circular reflectances of a chiral sculptured thin film backed by a metallic mirror contain strong evidence of the circular Bragg phenomenon. When the mirror is removed, strong evidence of that phenomenon is found only in the spectrum of the copolarized and cohanded reflectance.
Multiple surface-plasmon-polariton (SPP) waves can be guided by the interface of a metal and a chiral sculptured
thin film (STF). It is possible to embed within the chiral STF a layer of silver nanoparticles as sites to bind
recognition molecules for sensing analytes of a certain kind. Chiral STFs were deposited on aluminum thin films.
5-nm-thick layers of silver nanoparticles were deposited in the chiral STF at different depths in different samples.
The samples were then deployed in the Turbadar–Kretschmann–Raether configuration to observe the effects the
silver-nanoparticle layer had on the multiple SPP-wave modes in relation to the depth. We concluded that the
silver-nanoparticle layer tends to shift the angular locations of the SPP-wave modes but does not necessarily
affect the location of the SPP-wave modes to an extent that would render the data uninterpretable.
Tungsten-oxide thin films of three different morphologies-dense, columnar, and chiral-were fabricated by
evaporation at low pressure. The morphologies were observed using a scanning-electron microscope and their
optical transmission spectrums were also recorded. The CTF discriminated between normally incident light
of different linear polarization states. The chiral STF exhibited the circular Bragg phenomenon. Annealing
blue-shifted and widened the circular Bragg regime.
The propagation of a surface plasmon polariton (SPP) wave can be guided by the interface of a metal and a columnar thin film (CTF). Theory predicts that the angle of incidence on the prism/metal interface in the Turbadar–Kretschmann–Raether prism-coupled configuration required to excite the SPP wave shifts upon infiltration of the CTF by a fluid. Otherwise identical CTFs of different thicknesses were partnered with dense thin films of aluminum in optical experiments. The angle of incidence for exciting the SPP wave was found to shift to a higher value each time the CTF was infiltrated by a fluid of refractive index of increasing value. Experimental data indicated that the sensor offers a state-of-research sensitivity, thereby proving that a CTF can be a useful platform for SPP-wave-based optical sensing.
Multiple surface plasmon-polariton (SPP)-wave modes can be guided by the interface of a metal and a chiral sculptured thin film (STF). Theory predicts that the angular locations of SPP-wave modes will be shifted if the void regions of the chiral STF are infiltrated with a liquid. Therefore, chiral STFs of lanthanum fluoride were fabricated and employed as a partnering dielectric material to an aluminum thin film to guide multiple SPP-wave modes. The SPP-wave modes shifted to higher angular locations when the refractive index of the infiltrant was increased, exhibiting sensitivity comparable to state-of-research values. Thereby, surface multiplasmonics was exploited for optical sensing.
The propagation of a surface plasmon-polariton (SPP) wave can be guided by the interface of a metal and a columnar thin film (CTF). Theory predicts that the angle of incidence on the prism/metal interface in the Turbadar–Kretschmann–Raether prism-coupled configuration required to excite the SPP wave shifts upon infiltration of the CTF by a fluid. Otherwise identical CTFs of different thicknesses were partnered with dense thin films of aluminum in optical experiments. Regardless of the angle between the morphologically significant plane of the CTF and the cross-sectional plane of the prism, the angle of incidence for exciting the SPP wave was found to shift to a higher value when the CTF was infiltrated by a fluid of refractive index in excess of unity. Experimental data indicated that the angle between the morphologically significant plane of the CTF and the cross-sectional plane of the prism should not exceed about 45°◦ for high sensitivity.
Chiral sculptured thin films (STFs) produced by substrate rotation during physical vapor deposition exhibit the circular Bragg phenomenon, whereby normally incident left- and right-circularly polarized plane waves are discriminated in a spectral regime called the circular Bragg regime. Theory had predicted that substrate rocking, in synchrony with substrate rotation, during deposition could suppress the propensity to exhibit the circular Bragg phenomenon. Therefore chiral STFs of a dielectric material were fabricated with/without substrate rocking, and their transmittance spectrums for incident linearly and circularly polarized plane waves were measured. With sufficient rocking amplitude, the discrimination between incident left- and right-circularly polarized light nearly vanished, whereas a Bragg phenomenon for all normally incident plane waves was observed. Thus, chiral STF technology can be used to produce both ordinary and circular-polarization Bragg filters.
Chiral sculptured thin films (STFs) produced by substrate rotation during physical vapor deposition exhibit
the circular Bragg phenomenon, whereby normally incident left- and right-circularly polarized plane waves are
discriminated in a spectral regime called the circular Bragg regime. Theory had predicted that substrate rocking,
in synchrony with substrate rotation, during deposition, could suppress the propensity to exhibit the circular
Bragg phenomenon. Therefore, ZnSe chiral STFs were fabricated with/without substrate rocking, and their
transmittance spectrums for incident linearly and circularly polarized plane waves were measured. With sufficient
rocking amplitude, the discrimination between incident left- and right-circularly polarized light nearly vanished,
whereas a Bragg phenomenon for all normally incident plane waves was observed. Thus, chiral STF technology
can be used to produce both ordinary and circular-polarization Bragg filters.
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