Photonic nanojet (PNJ), the sub wavelength confinement of light by dielectric microspheres is finding applications in
nanoscale imaging, spectroscopy and nano lithography. These applications require control over the length and lateral
dimension of the nanojets. In the paper we present the results of numerical simulation to show that a core shell
microspheres can be used to generate photonic nanojet with controllable length and confinement by varying the
relative refractive index of the microspheres and the separation between the core and shell centers. We show that a
length of up to 27λ can be achieved when the core microsphere has lower refractive index than the shell and lateral
dimensions down to λ/3 with core microsphere having higher refractive index.
We have investigated the dependence of the Raman spectrum of an optically trapped red blood cell (RBC) on the orientation of the cell, relative to the polarization direction of the Raman excitation beam. The Raman scattered light polarized parallel to the polarization direction of the excitation beam was observed to depend upon the orientation of the cell. In particular, the heme bands at ∼754 cm−1 and in the 1500 to 1700 cm−1 region were observed to become maximum when the cells’ equatorial plane was parallel to the excitation beam polarization direction and minimum when the cells’ plane was normal to the polarization direction. In contrast, no significant orientational dependence was seen in the Raman scattered light polarized orthogonal to the polarization direction of the excitation beam. Theoretical simulations carried out to investigate these observations suggest that inside the RBCs, the hemoglobin molecules must be present in an ordered arrangement, such that heme-porphyrin planes become preferentially orientated parallel to the RBCs’ equatorial plane.
A reflection type white light diffraction phase microscope for full field surface profiling of opaque samples is proposed. The system can extract surface profile from one recorded interferogram without any mechanical movement and the use of white light makes it free from speckle noise. We validated the performance of our system by measuring a known step sample and a high-quality plane sample. The step height of the step sample is found to be 88.5 nm with a standard deviation of 1.4 nm, and the surface peak to valley value of the plane sample is found to be 28.6 nm with a standard deviation of 3 nm.
Raman spectroscopy was performed on optically trapped red blood cells (RBCs) from blood samples of healthy volunteers (h-RBCs) and from patients suffering from P. vivax infection (m-RBCs). A significant fraction of m-RBCs produced Raman spectra with altered characteristics relative to h-RBCs. The observed spectral changes suggest a reduced oxygen-affinity or right shifting of the oxygen-dissociation curve for the intracellular hemoglobin in a significant fraction of m-RBCs with respect to its normal functional state.
We report results of a study on the use of Laguerre-Gaussian (LG) modes for optical trapping of spermatozoa. The results show that for a given trap beam power the first-order LG mode (LG01) leads to lower photodamage to the cells without compromising the trapping efficiency.
Near-infrared laser (785-nm)-excited Raman spectra from a red blood cell, optically trapped using the same laser beam, show significant changes as a function of trapping duration even at trapping power level of a few milliwatts. These changes in the Raman spectra and the bright-field images of the trapped cell, which show a gradual accumulation of the cell mass at the trap focus, suggest photoinduced aggregation of intracellular heme. The possible role of photoinduced protein denaturation and hemichrome formation in the observed aggregation of heme is discussed.
The utilization of the enhanced local field near trapped metallic nanoparticles due to surface-plasmon resonance (SPR) for the optical trapping of dielectric fluorescent nano-objects is of considerable interest for single-molecule manipulation. Theoretical calculations as well as experimental measurements show that even with moderate SPR based field enhancement factors, gradient force based trapping of fluorescent molecules would be rather difficult. While trapping of the fluorescent molecule at resonance wavelength showed decreased stiffness, at wavelengths far away from resonance, increase in stiffness was found which was attributed to interplay of SPR-enhanced absorption and gradient forces.
The effect of oil vapor contamination on sol-gel porous silica antireflection (AR) coatings deposited on optics used in vacuum spatial filters of high-power lasers is experimentally studied. The contamination results in the reduction of laser-induced damage threshold (LIDT) and the increase in reflectivity of the AR coatings. In comparison, the silica coatings treated with ammonia and hexamethyl-disilazane (HMDS) show almost no increase of reflectivity, and their LIDT value reduces only marginally at the wavelength of laser operation. It is found that the decrease in LIDT of the coatings exposed to oil vapors occurs due to higher absorption of the laser light, as evidenced from the increase in the imaginary part of the refractive index of the coatings.
We report three-dimensional trapping of charge stabilized colloidal particles near a charged surface (glass
boundary), using a low numerical aperture objective. The trapping arises due to balancing action between optical forces
and electrostatic repulsions. The observation of 3-d colloidal clusters and a linear array of colloidal microspheres along
the trap beam and the possible reasons thereof are also discussed.
Polarization properties of any optical system are completely described by a sixteen-element (4 x 4) matrix called Mueller
matrix, which transform the Stokes vector describing the polarization properties of incident light to the stokes vector of
scattered light. Measurement of all the elements of the matrix requires a minimum of sixteen measurements involving both
linear and circularly polarized light. However, for many diagnostic applications, it would be useful if all the polarization
parameters of the medium (depolarization (Δ), differential attenuation of two orthogonal polarizations, that is, diattenuation
(d), and differential phase retardance of two orthogonal polarizations, i.e., retardance (δ )) can be quantified with linear
polarization measurements alone. In this paper we show that for a turbid medium, like biological tissue, where the
depolarization of linearly polarized light arises primarily due to the randomization of the field vector's direction by multiple
scattering, the polarization parameters of the medium can be obtained from the nine Mueller matrix elements involving linear
polarization measurements only. Use of the approach for measurement of polarization parameters (Δ, d and δ) of normal and
malignant (squamous cell carcinoma) tissues resected from human oral cavity are presented.
Failure of endodontic treatment is commonly due to Enterococcal infection. In this study influence of chemical
treatments of type-I collagen membrane by chemical agents commonly used in endodontic treatment on Enterococcus
faecalis cell adherence was evaluated. In order to determine the change in number of adhering bacteria after chemical
treatment, confocal laser scanning microscopy was used. For this, overnight culture of E faecalis in All Culture broth
was applied to chemically treated type-I collagen membrane. It was found that Ca(OH)2 treated groups had statistically
significant (p value=0.05) increase in population of bacteria adherence. The change in adhesion force between bacteria
and collagen was determined by using optical tweezers (1064 nm). For this experiment, Type-I collagen membrane was
soaked for 5 mins in a media that contained 50% all culture media and 50% saturated Ca(OH)2 . The membrane was
spread on the coverslip, on which diluted bacterial suspension was added. The force of laser tweezers on the bacteria was
estimated at different trap power levels using viscous drag method and trapping stiffness was calculated using
Equipartition theorem method. Presence of Ca(OH)2 was found to increase the cell-substrate adherence force from
0.38pN to >2.1pN. Together, these experiments show that it was highly probable that the increase in adherence to
collagen was due to a stronger adhesion in the presence of Ca (OH)2.
Microscopic objects can be manipulated in a more complex and effective way by use of static aberrated tweezers. We
theoretically studied dynamics of interaction of Rayleigh particles with such asymmetric tweezers. Microscopic objects
are pulled at the high intensity gradient end of the asymmetric tweezers, get accelerated and are ejected from the other
end. Thus objects from two locations could be transported by two asymmetric line tweezers and mixed at another place
where the low intensity gradient regions of the two beams meet. It is pertinent to note here that the speed of transport is
determined by the laser beam power and the degree of asymmetry in the intensity profile. And since for a fixed
asymmetry and laser power, the speed is dependent on the refractive index and size of the objects, sorting of these
objects could be made possible. Sorting could be achieved either by scanning the asymmetric line tweezers across the
sample or without scanning the stage by use of two asymmetric line tweezers. In the all-optical approach (use of two
asymmetric line tweezers), we exploited the fact that when the speed of objects transported by one tweezers crossed a
threshold value, these did not interact with the second tweezers and therefore moved undeviated; whereas slower
moving objects were collected by the second tweezers and transported to a well-separated location.
We report the use of a chemically etched tapered single mode fiber tip for enhancing lateral resolution in optical
coherence tomography (OCT). The important advantage of this approach is that high lateral resolution is achieved,
without compromising the depth of imaging, as is the case with the use of high numerical aperture (NA) objectives. Use
of the tapered tip in the sample arm of a single mode fiber based set-up allowed visualization of intracellular structures
of Elodea densa plant leaf that could not be seen by the conventional OCT.
Recently, we have reported self-rotation of normal red blood cells (RBC), suspended in hypertonic buffer, and trapped in unpolarized laser tweezers. Here, we report use of such an optically driven RBC-motor for microfluidic applications such as pumping/centrifugation of fluids. Since the speed of rotation of the RBC-motor was found to vary with the power of the trapping beam, the flow rate could be controlled by controlling the laser power. In polarized optical tweezers, preferential alignment of trapped RBC was observed. The aligned RBC (simulating a disk) in isotonic buffer, could be rotated in a controlled manner for use as a microfluidic valve by rotation of the plane of polarization of the trapping beam. The thickness of the discotic RBC could be changed by changing the osmolarity of the solution and thus the alignment torque on the RBC due to the polarization of the trapping beam could be varied. Further, in polarized tweezers, the RBCs in hypertonic buffer showed rocking motion while being in rotation. Here, the RBC rotated over a finite angular range, stopped for some time at a particular angle, and then started rotating till it was back to the aligned position and this cycle was found repetitive. This can be attributed to the fact that though the RBCs were found to experience an alignment torque to align with plane of polarization of the tweezers due to its form birefringence, it was smaller in magnitude as compared to the rotational torque due to its structural asymmetry in hypertonic solution. Changes in the laser power caused a transition from/to rocking to/from motor behavior of the RBC in a linearly polarized tweezers. By changing the direction of polarization caused by rotation of an external half wave plate, the stopping angle of rocking could be changed. Further, RBCs suspended in intermediate hypertonic buffer and trapped with polarized tweezers showed fluttering about the vertical plane.
We report the use of light scattering to monitor the morphological changes in mammalian breast cancer cells (MCF-7)
undergoing UVA irradiation induced apoptosis. The values for the scattering anisotropy parameter (g) and reduced scattering
coefficient [μs/ = μs (1-g), where μs is the scattering coefficient] of the control cell suspensions and cell suspensions
irradiated to varying dosage of UVA (80 - 160 kJ / m2) were estimated for the wavelength range 450nm - 750 nm using
integrating sphere measurements of diffuse reflectance and transmittance. These estimates were used to determine the Mie
equivalent scatterer radius (r Mie) and thus quantify the morphological alterations of the cells. The value for r Mie was
observed to decrease monotonically with increase in the UVA dose to up to a dose of 140 KJ/m2 and showed an increasing
behavior beyond this dose. Since it is known that while apoptosis leads to shrinkage in volume of the cells and fragmentation
of nuclei, necrosis of the cells is associated with a swelling of cells, the results suggest that at doses below 1 40 kJ/m2 cells
undergo apoptosis and beyond this dose necrosis takes place. We also used the light scattering approach to monitor effect of
He-Ne pre-irradiation on UVA induced damage in cells. Results were consistent with previous reports that suggest that He-
Ne pre-irradiation can induce protection against the UVA damage to the cells.
For in vivo determination of optically active (chiral) substances in turbid media, like for example glucose in human tissue,
the backscattering geometry is particularly convenient. However, recent polarimetric measurements performed in the
backscattering geometry have shown that, in this geometry, the relatively small rotation of the polarization vector arising due
to the optical activity of the medium is totally swamped by the much larger changes in the orientation angle of the
polarization vector due to scattering. We show that the change in the orientation angle of the polarization vector arises due to
the combined effect of linear diattenuation and linear retardance of light scattered at large angles and can be decoupled from
the pure optical rotation component using polar decomposition of Mueller matrix. For this purpose, the method developed
earlier for polar decomposition of Mueller matrix was extended to incorporate optical rotation in the medium. The validity of
this approach for accurate determination of the degree of optical rotation using the Mueller matrix measured from the
medium in both forward and backscattering geometry was tested by conducting studies on chiral turbid samples prepared
using known concentration of scatterers and glucose molecules.
We report the application of a support vector machine (SVM) for the development of diagnostic algorithms for optical diagnosis of cancer. Both linear and nonlinear SVMs have been investigated for this purpose. We develop a methodology that makes use of SVM for both feature extraction and classification jointly by integrating the newly developed recursive feature elimination (RFE) in the framework of SVM. This leads to significantly improved classification results compared to those obtained when an independent feature extractor such as principal component analysis (PCA) is used. The integrated SVM-RFE approach is also found to outperform the classification results yielded by traditional Fisher's linear discriminant (FLD)-based algorithms. All the algorithms are developed using spectral data acquired in a clinical in vivo laser-induced fluorescence (LIF) spectroscopic study conducted on patients being screened for cancer of the oral cavity and normal volunteers. The best sensitivity and specificity values provided by the nonlinear SVM-RFE algorithm over the data sets investigated are 95 and 96% toward cancer for the training set data based on leave-one-out cross validation and 93 and 97% toward cancer for the independent validation set data. When tested on the spectral data of the uninvolved oral cavity sites from the patients it yielded a specificity of 85%.
Larger depolarization of incident polarized light has been reported for tissues compared to tissue phantoms with matched optical thickness (? =?s × d, ?s being the scattering coefficient and d the physical thickness). We show that this arises because for the sample with larger ?s more multiply scattered photons are detected in a narrow collection angle typically used in experiments. These results were verified by time resolved studies on transmitted light as well as by Monte Carlo simulation.
A theoretical treatment based on electromagnetic theory has been developed for the dependence of depolarization of linearly and circularly polarized light on size parameter of scatterer. The model reproduces the earlier results for the dependence of depolarization of circularly and linearly polarized light on scatterer size parameter. Further, the results obtained from this model show that for a given scatterer size parameter, a change in the value of ratio of refractive index of scatterer to that of the surrounding medium also significantly affects the degree of depolarization of both linearly and circularly polarized light. These results have been experimentally verified and can have important consequences for polarization gated optical imaging.
KEYWORDS: Photodynamic therapy, Tumors, Tissues, Luminescence, Mathematical modeling, In vivo imaging, Diffusion, Data modeling, Laser therapeutics, Cancer
In the recent years (delta) -aminolevulinic acid ((delta) -ALA) a precursor for the endogenous production of protoporphyrin IX (PPIX) has gained importance in the Photodynamic Therapy (PDT) of superficial and early-stage cancers. Though (delta) -ALA is present naturally in the cells, systemic administration of exogenous (delta) -ALA leads to the production of intracellular endogenous PP IX in both the tumor and the normal cells, but with varying concentration. However, the PPIX is accumulated more in the tumor tissues as the fast growing tumor cells take up the administered (delta) -ALA more than the normal cells. As the therapeutic efficacy of PDT is dependent on the post (delta) -ALA incubation time, at which the tumor to normal ratio of the PPIX concentration is high, the concentration of the PPIX in the normal and the tumor site were estimated using fluorescence spectroscopy. However, the estimation of the PPIX concentration during/after PDT is mandatory, as the PDT dosimetry is dependent on the sensitizer concentration at the target of interest. The observed variation in the concentration of PPIX in the tumor site with respect to the unexposed normal surrounding tissues, may be attributed to the diffusion of PPIX from the surrounding normal tissues to the tumor site, across the concentration gradient. Based on this a mathematical model has been proposed, to estimate the rate parameter for the diffusion of PPIX from the surrounding normal tissues in to the tumor tissue (Km), due to photobleaching during PDT at two different fluence. The Km value at two different fluences, 57.6 and 36 J/cm2 are estimated as 5.444+/- 1.186 and 3.221+/- 0.957, respectively. Further, the rate parameter for the cleavage and efflux of (delta) -ALA (K1), and the rate parameter for the evasion of the PPIX from the tumor tissues during PDT (Kt), were also estimated by fitting the experimental data to the developed mathematical model. The estimated parameters will be utilized to estimate the exact concentration of PPIX in the tumor tissues for a better PDT efficacy.
In this work high resolution Fourier transform infrared (IR) spectra corresponding to the OCD-bending, C-O stretching and CH2-rocking bands of methyl alcohol-D1 have been recorded in the range 815-1120 cm-1, at a resolution of cm-1. Analysis of the OCD bending mode transitions yielded identification of quantum numbers involved for far Infrared (FIR) laser lines optically pumped by the 10P(34) and 10P(46) CO2 laser lines. The observed wavenumbers for the OCD bending transitions relevant to the laser assignments are presented. The IR assignments are confirmed by forming close combination loops of observed R, P, and Q branch transitions. The results are in agreement with microwave (MW) analysis.
In this work, the high resolution infrared (IR) spectrum of C-13 substituted methyl alcohol corresponding to the C-O stretch vibration and far infrared (FIR) spectrum corresponding to the torsional-rotational transitions have been recorded using a Fourier transform spectrometer. The results of the detailed analysis on the spectra have been applied to proposed new assignments of FIR laser lines pumped by the 9P(34) CO2 laser line. These assignments involve highly interacted first excited C-O stretch vibrational state. The assignments are supported by closed combination loops of accurately measured IR and FIR transitions. The analysis also yielded accurate frequencies for seventeen potential FIR laser lines in C-13 methanol. The spectral data relevant to this work are presented. The FIR absorption spectroscopic study allowed us to evaluate the leading torsional-rotational molecular parameters for 13CH3OH in the vibrational ground state. In addition, comments are also made on the identification of FIR laser lines in 13CD3OH pumped by the 10P(24) CO2 laser line. The results will be useful for a precise model of the Hamiltonian for excited C-O stretching state.
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.