Optical Ruler Research Articles

Real-Time Measurement and Uncertainty Evaluation of Optical Path Difference in Fiber Optic Interferometer Based on Auxiliary Interferometer.

Optical interferometers are the main elements of interferometric sensing and measurement systems. Measuring their optical path difference (OPD) in real time and evaluating the measurement uncertainty are key to optimizing system noise and ensuring system consistency. With the continuous sinusoidal wavelength modulation of the laser, real-time OPD measurement of the main interferometer is achieved through phase comparison of the main and auxiliary interferometers. The measurement uncertainty of the main interferometer OPD is evaluated. It is the first evaluation of the impact of different auxiliary interferometer calibration methods on OPD measurements. A homodyne quadrature laser interferometer (HQLI) is used as the main interferometer, and a 3 × 3 interferometer is used as the auxiliary interferometer. The calibration of the auxiliary interferometer using optical spectrum analyzer scanning and ruler measurement is compared. The evaluation shows that the auxiliary interferometer is the most significant source of uncertainty and causes the total uncertainty to increase linearly with increasing OPD. It is proven that a high-precision calibration and large-OPD auxiliary interferometer can improve the real-time accuracy of OPD measurements based on the auxiliary interferometer. The scheme can determine the minimum uncertainty to optimize the system noise and consistency for vibration, hydroacoustic, and magnetic field measurements with OPDs of the ~m level.

Prosthetic approach following traumatic evisceration: a case report

A 20-year-old male patient was referred to Prosthodontic Department, Dental Hospital of Hasanuddin University, Makassar with chief complaint of disfiguration of the face. Medical history revealed a significant trauma to the left eye 6 months prior which stayed after evisceration. Patient has never used prosthetic eye afterwards. Examination of the left eye socket revealed a healthy conjunctiva covering the posterior wall of the anophthalmic socket with syn-chronous motions and absence of infection or inflammation signs. Sulcus depth was sufficient enough to retain prosthetic eye. This article presents rehabilitation of the ocular defect with customized acrylic-based ocular prosthe-sis to increase patient’s appearance and to prevent further shrinkage of the eye socket. Preliminary impression was done using customized tray fabricated from modelling wax and hydrocolloid irreversible impression material. An in-traocular custom tray for secondary impression was fabricated with acrylic resin and modified with a syringe that at-tached to the custom tray. Secondary impression of the defect was recorded using polyvinyl siloxane light viscosi-ty material followed by wax pattern fabrication using modelling wax. The wax pattern was tried in patient’s socket and checked for size, comfort, support, fullness, and then packed with tooth colored heat cure acrylic resin. After deter-mining the location and diameter of the iris with an optical vernier pupillary distance ruler, the color of sclera was de-termined by shade guide and confirmed with technician using digital photo. Ocular prosthesis was fabricated after-wards and inserted into the eye socket and evaluated for suitability, aesthetic and also movements with the contra-lateral eye. It is concluded that customized ocular prosthesis was significantly more aesthetic than pre-fabricated one with better contouring, color matching, and coordinated movements with the contralateral eye. This prosthetic ap-proach may restore patient’s appearance, increase their self-esteem, and improve their quality of life.

Movable Optical Frequency Ruler with Optical Activity

Optical frequency rulers (OFR) are suggested for use as optical wavelength or frequency references for spectra manipulation or unknown wavelength measurement. In the past, complicated mechanisms that are not easy to utilize were used to make OFR, such as a double-slits with a high-speed fluid or an external circuit to control the liquid crystal birefringence. This work introduces a simple structure to produce an OFR, which should be easier to implement. It utilizes quartz block optical activity and two polarizers. Because of the strong wavelength dependence of the rotatory power, each wavelength component in the spectrum experiences a different amount of polarization angle rotation. Some components whose angles are perpendicular to that of the analyzer are filtered out and naturally form the OFR’s ticks. The numerical results show that those spectral ticks can be moved to higher or lower wavelengths by rotating the analyzer’s angle. This scheme provides another possibility for creating movable OFR with the merit of easy usage.

The effect of atropine used in dobutamine stress echocardiography on pupil diameter.

The use of atropine during dobutamine stress echocardiography (DSE) is contraindicated in persons with narrow angle glaucoma though there is limited evidence that low doses of intravenous atropine do not cause pupillary dilation. The aim of this study is to investigate whether atropine when administered in persons without glaucoma during dobutamine stress echocardiography causes pupillary dilation. Out of 144 patients without a history of glaucoma referred for DSE for clinical indications, 105 patients received intravenous atropine doses ranging from 0.1 mg to 1.25 mg (most patients received 0.25-0.75 mg). Pupil diameter of both eyes was measured under the same light conditions before and after the DSE using a CP-30 Optical Digital PD Ruler. For the total of 210 examined eyes pupil diameter remained unaltered after each DSE test (3.65 ± 0.799 mm before vs 3.63 ± 0.766 mm after, p = .737). Similarly, pupil diameter remained unchanged when left and right eyes were assessed separately (right eye: 3.770 ± 0.812 before vs 3.752 ± 0.745 mm after, p = .821 and left eye: 3.521 ± 0.770 before vs 3.499 ± 0.770 mm after, p = .806). Diameter of right and left pupil were also unaltered after grouping patients by sex and iris pigmentation. Age, weight, atropine dose and propranolol dose were not correlated with changes in pupil diameter. Intravenous atropine in usual doses administered in DSE does not cause mydriasis in adults without glaucoma. Future studies need to confirm our findings and expand the investigation regarding safety of atropine use during DSE in patients with narrow angle glaucoma.

Frequency-comb-calibrated swept-wavelength interferometry.

Lasers are often used to characterize samples in a non-destructive manner and retrieve sensing information transduced in changes in amplitude and phase. In swept wavelength interferometry, a wavelength-tunable laser is used to measure the complex response (i.e. in amplitude and phase) of an optical sample. This technique leverages continuous advances in rapidly tunable lasers and is widely used for sensing, bioimaging and testing of photonic integrated components. However, the tunable laser requires an additional calibration step because, in practice, it does not tune at a constant rate. In this work, we use a self-referenced frequency comb as an optical ruler to calibrate the laser used in swept-wavelength interferometry and optical frequency domain reflectometry. This allows for realizing high-resolution complex spectroscopy over a bandwidth exceeding 10 THz. We apply the technique to the characterization of low-loss integrated photonic devices and demonstrate that the phase information can disentangle intrinsic from coupling losses in the characterization of high-Q microresonators. We also demonstrate the technique in reflection mode, where it can resolve attenuation and dispersion characteristics in integrated long spiral waveguides.

Compact cold atom gravimeters and precise gravity measurement

Atomic gravimetry measures the gravitional acceleration of an ensemble of identical neutral atoms through the atom interferometry based on Raman two-photon transition, where the Raman lasers are used as “optical ruler" and the identical neutral atoms play the role of test mass and quantum storage of gravity field information. As the novel gravimetry system suffers no mechanical wear and works at a higher repetition rate, atom gravimetry can reach a much better short-term sensitivity than the classical falling-corner-cube counterpart, and the accuracy is reasonably well. Since the very first in-laboratory device built over 30 years ago, atomic gravimetry has matured to a versatile tool that offers both precise and accurate absolute gravity measurement to fundamental research and metrology, such as testing the weak equivalence principle or linking the mass and weight of the test mass in Watt (Kibble) balance. As the current rapid development of compact cold-atom gravimeters, atomic gravimetry is moving out of the laboratory to be used as a quantum enhancement of classical devices in dynamical measurement, such as geophysics survey, inertial navigation and space mission. We review the roadmap for the development of cold-atom absolute gravimetry, highlight recent advances in the dynamical measurement using compact cold atom gravimeters and discuss the associated technological challenges. In the future, with the maturity of its application in dynamical measurement or civil engineering and the innovation in atom interferometry theory, atomic gravimetry could play a more and more important role in our life.

Slit Diffraction Spectrum Manipulation in Non-Paraxial Regions via the Spatial-Spectral Correspondence Relationship

In the past, a two-dimensional aperture diffraction of light in the non-paraxial region could only be studied using the Huygens integral without functional forms. This work presents a special case—a one dimension slit where the functional form can be obtained. The monochromatic light intensity distributions are investigated in detail. Using the correspondence relationship, the diffracted spectra of polychromatic light in that region can be readily found. Three interesting spectral effects are described: spectral switches, multi-level data transmission, and optical wavelength ruler. Since the functional form is derived without approximation, it is applicable to a region very near to the slit, including the wavelength region or even sub-wavelength scale. Thus, for light with micron-order wavelength (visible to near infrared (NIR) band), these results are valuable to micro- or nano-optics, especially for studies of the spatial intensities or spectral characteristics in the non-paraxial region.

Liquid crystal based spectral control for applications in optical communication and metrology

The molecules of nematic liquid crystals (LCs), aligned in one average direction, constitute a birefringent medium. The molecules in nematic LCs of positive anisotropy (ne>no) get aligned in the direction of applied electric field due to the induced dipoles, which results in modification in the birefringence of this medium by applying the voltage. Being an electro-optical medium, the broadband spectra passing through the nematic LCs can be manipulated by the application of voltage. We demonstrate both theoretically and experimentally a tunable optical frequency ruler and a spectral switch using voltage application across the LCs. The tunable optical frequency ruler finds application in identifying an unknown spectral line in the given spectra suitable for optical metrology applications. The LC based spectral switch, which can be controlled several orders of magnitude faster then its mechanical counterpart, is used in a proposed scheme for efficient spectral shift based data encoding and decoding in free-space based optical communication. We also demonstrate theoretically and experimentally, the tunability in spectral width selection by rotating the LC cell placed between the two cross-polarizers. It may be useful in the situations where a tunable spectral bandwidth source is of prime importance.

Three-Dimensional Two-Color Dual-Particle Tracking Microscope for Monitoring DNA Conformational Changes and Nanoparticle Landings on Live Cells.

Here, we present a three-dimensional two-color dual-particle tracking (3D-2C-DPT) technique that can simultaneously localize two spectrally distinct targets in three dimensions with a time resolution down to 5 ms. The dual-targets can be tracked with separation distances from 33 to 250 nm with tracking precisions of ∼15 nm (for static targets) and ∼35 nm (for freely diffusing targets). Since each target is individually localized, a wealth of data can be extracted, such as the relative 3D position, the 2D rotation, and the separation distance between the two targets. Using this technique, we turn a double-stranded DNA (dsDNA)-linked dumbbell-like dimer into a nanoscopic optical ruler to quantify the bending dynamics of nicked or gapped dsDNA molecules in free solution by manipulating the design of dsDNA linkers (1-nick, 3-nt, 6-nt, or 9-nt single-strand gap), and the results show the increase of kon (linear to bent) from 3.2 to 10.7 s-1. The 3D-2C-DPT is then applied to observe translational and rotational motions of the landing of an antibody-conjugated nanoparticle on the plasma membrane of living cells, revealing the reduction of rotations possibly due to interactions with membrane receptors. This study demonstrates that this 3D-2C-DPT technique is a new tool to shed light on the conformational changes of biomolecules and the intermolecular interactions on plasma membrane.

Direct observation of dynamic thermal lensing in nanoscale surfaces/interfaces of end-pumped Nd:YVO4 laser

This work describes non-invasive observations of dynamic thermal lensing in an end-pumped Nd:YVO4 laser. Measurements were obtained with a nanoscale optical ruler created using chromatic aberrations, pinholes, dispersive gratings, and position-sensitive detectors. This study reports on variations in thermally induced oscillations and on underdamping behavior in the regime of high pump power. Dynamic data related to the thermal behavior can be used to study the balance between driving forces (pumping and thermal stresses) and damping losses (cooling and output coupling). The non-invasive nature of the proposed scheme along with its sub-100-nm axial resolution, sub-millisecond time resolution, and simple configuration makes it widely applicable for studying heat-related phenomena within laser crystals. The preliminary results show that such non-invasive methods could be used to detect thermally induced nanoscale deformations in integrated circuits, high-power optoelectronic devices, and optical devices with high-power illumination.

Detecting nanometric displacements with optical ruler metrology.

We introduce the optical ruler, an electromagnetic analog of a physical ruler, for nanoscale displacement metrology. The optical ruler is a complex electromagnetic field in which singularities serve as the marks on the scale. It is created by the diffraction of light on a metasurface, with singularity marks then revealed by high-magnification interferometric observation. Using a Pancharatnam-Berry phase metasurface, we demonstrate a displacement resolving power of better than 1 nanometer (λ/800, where λ is the wavelength of light) at a wavelength of 800 nanometers. We argue that a resolving power of ~λ/4000, the typical size of an atom, may be achievable. An optical ruler with dimensions of only a few tens of micrometers offers applications in nanometrology, nanomonitoring, and nanofabrication, particularly in the demanding and confined environment of future smart manufacturing tools.

Spectral manipulation and tunable optical frequency ruler using liquid crystal’s birefringence

The polarization control method using a birefringent solid crystal produces only fixed optical frequency rulers and complementary spectra. A configuration using liquid crystal (LC) improves and extends above method’s ability to control incident polychromatic light spectra. It is shown that, by adjusting the voltage applied to the LC module, the induced birefringence and phase shift can be controlled in a wide range; consequently, this scheme can be employed to realize tunable optical frequency ruler, spectral switches, and spectrum compression. Compared with the previous one, this work provides an easier, and more powerful way to manipulate polychromatic light, which benefits its future applications, such as optics communication, spectra control, etc.

Chromatic confocal microscopy to rapidly reveal nanoscale surface/interface topography by position-sensitive detection

This paper presents a confocal microscope for the rapid and noninvasive capture of three-dimensional (3D) images showing the surface/interface topography in a far-field configuration. The proposed microscope features a nanoscale optical ruler capable of performing fast depth measurements based on the chromatic aberration of microscope objectives. A diffraction grating and a position-sensitive detector were used to extract the spectral shift, which directly maps the height of the surface with a nanoscale resolution. Because neither the mechanical scanning nor the spectrometer, which limit the speed of 3D imaging, are needed in the axial direction, full 3D surface topography images with nanoscale depth resolution can be acquired rapidly using the nanoscale optical ruler in conjunction with 2D lateral beam scanning. The presented technique overcomes the limitation of the detection speed of conventional chromatic confocal microscopy. In experiments, the 3D static and dynamic nanoscale surface profiles of several representative optoelectronic and electronic devices were demonstrated. This fast and non-invasive approach with nanoscale depth resolution to the measurement of topography images has considerable promise in academic research and industrial applications.

Determination of hyperfine structure constants of 5D5/2 and 7S1/2 states of rubidium in cascade atomic system

We present a method to precisely determine the hyperfine structure constants of the rubidium 5D5/2 and 7S1/2 states in a cascade atomic system. The probe laser is coupled to the 5S1/2→5P3/2 hyperfine transition, while the coupling laser is scanned over the 5P3/2→5D5/2(7S1/2) transition. The high-resolution double-resonance optical pumping spectra are obtained with two counter-propagating laser beams acting on rubidium vapor. The hyperfine splitting structures are accurately measured by an optical frequency ruler based on the acousto-optic modulator, thus, the magnetic dipole hyperfine coupling constant A and quadrupole coupling constant B are determined. It is of great significance for the atomic hyperfine structure and fundamental physics research.

Spectral manipulation and complementary spectra with birefringence polarization control

A polarization control method using crystal birefringence is suggested to manipulate polychromatic light. This scheme can be used with narrower bandwidth to produce various spectral effects, such as a notch filter, a flat top, and triangle-type, nipple-type, and central-frequency-dominant distributions. A modulated spectrum with greater bandwidth can be used as an optical frequency ruler, and phenomena called complementary spectra are also proposed, where the two spectral distributions, produced by rotating the polarizer, complement each other in the sense that the peaks and valleys in one spectrum are the reverse in the other. These results benefit the controlling of the spectral shape and the measurement of an unknown optical frequency.

Molecular interactions of organic molecules at the air/water interface investigated by sum frequency generation vibrational spectroscopy

The molecular structure and dynamics of organic molecules at the aqueous interface have attracted a number of investigations owing to their importance and specific nature. However, there are relatively few studies on the direct characterization of the molecular interactions at the air/water interface because they are extremely difficult to measure in experiments. In this study, we use dibutyl ester molecules (R1CO2R2O2CR1) as a model of organic molecules, and investigate their molecular structure and interactions using sum frequency generation vibrational spectroscopy. We demonstrate that the molecular interactions can be estimated by measuring the intensity ratio of the symmetric stretching (ν1) and Fermi resonant bands (2ν2) of methyl groups. Here, dibutyl ester molecules are widely used as plasticizers in polymers to improve the properties of the plastics and polymers. It is found that the orientation angles of the tailed methyl groups at the air/water interface decrease from 34° to 19° when the chain length of R2 increases from 0 to 8. The total intermolecular interactions of the dibutyl ester molecules decrease as the chain length of R2 increases because the van der Waals interactions between the hydrocarbon chains increase, while the hydrogen bond interactions between the carbonyl group and water molecules decrease. Our study demonstrates the stability of ester-based plasticizers in polymers can be well predicted from the intensity ratio of the ν1 and 2ν2 bands of methyl group. Such an intensity ratio can be thus used as an effective vibrational optical ruler for characterizing molecular interactions between plasticizers and polymers.

Triangulating Nucleic Acid Conformations Using Multicolor Surface Energy Transfer.

Optical ruler methods employing multiple fluorescent labels offer great potential for correlating distances among several sites, but are generally limited to interlabel distances under 10 nm and suffer from complications due to spectral overlap. Here we demonstrate a multicolor surface energy transfer (McSET) technique able to triangulate multiple points on a biopolymer, allowing for analysis of global structure in complex biomolecules. McSET couples the competitive energy transfer pathways of Förster Resonance Energy Transfer (FRET) with gold-nanoparticle mediated Surface Energy Transfer (SET) in order to correlate systematically labeled points on the structure at distances greater than 10 nm and with reduced spectral overlap. To demonstrate the McSET method, the structures of a linear B-DNA and a more complex folded RNA ribozyme were analyzed within the McSET mathematical framework. The improved multicolor optical ruler method takes advantage of the broad spectral range and distances achievable when using a gold nanoparticle as the lowest energy acceptor. The ability to report distance information simultaneously across multiple length scales, short-range (10-50 Å), mid-range (50-150 Å), and long-range (150-350 Å), distinguishes this approach from other multicolor energy transfer methods.

Subnanometer-accuracy optical distance ruler based on fluorescence quenching by transparent conductors

Available data: Complex refractive index of Indium Tin Oxide, http://dx.doi.org/10.4121/uuid:59febf27-a532-4ac9-8ec0-29d4195b2c8c Transparent conductive oxides (TCOs), such as the well-known indium-tin oxide, find widespread use in modern (nano)technological applications because of their unique combination of negligible optical absorption and good electric conductivity. We, however, show that despite the near-zero imaginary part of the refractive index that is responsible for the material’s transparency, TCOs drastically quench optical emitters when the emitter is within 10 nm from the TCO. Our results reveal that the pure near-field nature of this dissipation makes for an exquisite short-range optical ruler. Previous quenching-based optical rulers, based on interactions with plasmonic or graphene materials, have allowed measuring distances in the 20–100 nm range. Distances below 20 nm have, however, been hard to assess due to poor photon yields or weak absolute variations. We show that TCO-based rulers close this gap, allowing distance measurements with far-field optics in the 1–10 nm distance range with deep subnanometer sensitivity.

Intermolecular Interactions at the Interface Quantified by Surface-Sensitive Second-Order Fermi Resonant Signals

Accurate determination of intermolecular interaction forces at the surface and the interface is essential to identify the nature of interfacial phenomena such as absorption, interfacial assembly, and specific ion effect, but it still represents a major technical challenge. In this study, we proposed a novel method to deduce the interfacial interaction forces by using surface-sensitive second-order Fermi resonant signals, generated in sum frequency generation vibrational spectroscopy (SFG-VS). By investigating the influence of lipid chain length and intermolecular distance on the Fermi resonant signals of phospholipid monolayer at the air/CaF2 surface and the air/water interface, a linear correlation between the Fermi resonant intensity ratio and the dominated interactions in the lipid monolayer has been observed. It implies that the amplitude of the intensity ratio can be used as an effective in situ vibrational optical ruler to characterize the total intermolecular interaction forces at the surface and t...

Tailoring of optical properties of fluorescein using green synthesized gold nanoparticles.

Dye-nanoparticle mixtures hold great promise in biological as well as photonics applications due to their capability to tailor the emission behavior of dye by tuning the nanoparticles parameters. However, as compared to the well-defined dye-nanoparticle distance, studies lack the understanding of homogenous mixtures of dye and nanoparticles. In this work, we investigate the influence of shape and concentration of gold nanoparticles prepared via green synthesis on the optical properties of fluorescein dye in a dye-nanoparticle mixture. We have investigated the radiative path of deexcitation using steady state fluorescence and the non-radiative path is probed using a laser based dual-beam thermal lens technique. The energy transfer efficiency as well as dye-nanoparticle distance is studied using both techniques. Furthermore, we have explored the influence of nanoparticles parameters on the fluorescence quantum yield of fluorescein using the thermal lens technique. The studies indicate that spherical nanoparticles are efficient quenchers while star shaped nanoparticles can probe larger dye-NP distances. The tailoring of dye properties by tuning nanoparticle parameters can be utilized in diverse areas including bioimaging, solar cells, and sensors.