Irfan Ahmed

Charge transport through split photoelectrodes in dye-sensitized solar cells

Charge transport and recombination are relatively ignored parameters while upscaling dye-sensitized solar cells (DSCs). Enhanced photovoltaic parameters are anticipated by merely widening the devices physical dimensions, viz., thickness and area as evident from the device design adopted in reported large area DSCs. These strip designs lead to ≤50% loss in photocurrent compared to the high efficiency lab scale devices. Herein, we report that the key to achieving higher current density (JSC ) is optimized diffusion volume rather than the increased photoelectrode area because kinetics of the devices is strongly influenced by the varied choices of diffusion pathways upon increasing the electrode area. For a given electrode area and thickness, we altered the photoelectrode design by splitting the electrode into multiple fractions to restrict the electron diffusion pathways. We observed a correlation between the device physical dimensions and its charge collection efficiency via current-voltage and impedance spectroscopy measurements. The modified electrode designs showed >50% increased JSC due to shorter transport time, higher recombination resistance and enhanced charge collection efficiency compared to the conventional ones despite their similar active volume (∼3.36 × 10−4 cm3). A detailed charge transport characteristic of the split devices and their comparison with single electrode configuration is described in this article.

Two-dimensional Talbot self-imaging via Electromagnetically induced lattice

We propose a lensless optical method for imaging two-dimensional ultra-cold atoms (or molecules) in which the image can be non-locally observed by coincidence recording of entangled photon pairs. In particular, we focus on the transverse and longitudinal resolutions of images under various scanning methods. In addition, the role of the induced nonmaterial lattice on the image contrast is investigated. Our work shows a non-destructive and lensless way to image ultra-cold atoms or molecules that can be further used for two-dimensional atomic super-resolution optical testing and sub-wavelength lithography.

Elemental analysis of the thyroid by laser induced breakdown spectroscopy

The thyroid is an important hormone regulation organ. Laser induced breakdown spectroscopy (LIBS) is developed to assess iodine and other essential elements in the thyroid (of rats). Subjects are administered 0.05% iodine water for 0, 6, and 12 days before the thyroid is extracted. Pronounced iodine, sodium, calcium, and potassium emissions are observed at approximately 746, 589, 395/422, and 766/770 nm, respectively. Iodine emission is surprisingly highest in 0 day subjects, lowest after 6 days, and recovers by 12 days. This follows the Wolff-Chaikoff effect as ingestion of excess iodine reduces thyroid iodine and iodine is essential for hormone production. LIBS is a promising method for trace elemental analysis of the thyroid.

Second-order self-imaging with parametric amplification four-wave mixing

By modulating the emission characteristics of a twin-correlated bright beam in a parametric amplification of the four-wave mixing process, a nondestructive and lensless imaging scheme to image ultra-cold atoms or molecules is proposed. The optical lattice state, which is induced via the coupling between ultra-cold atoms and a standing wave, is used to effectively modulate the dressing-suppressed/enhanced nonlinear susceptibility, and an emission-intensity-modulated grating of a correlated bright beam is formed. The intensity fluctuations of the correlated bright beam are taken as the imaging light to implement second-order coincidence measurement. As an important complementary scheme to a previous self-imaging scheme with spontaneous parametric down-conversion, our scheme has the characteristic of an efficient generation and detection rate. In addition, the visibility of the imaging can be significantly improved by enhanced nonlinear susceptibility. Our work may offer a nondestructive and lensless way to image ultra-cold atoms or molecules.

Spectroscopic examination of enamel staining by coffee indicates dentin erosion by sequestration of elements

The mechanism of coffee eliciting erosion on teeth is unclear as few studies have investigated the direct effect of coffee on enamel and dentin structures. The present study identified how coffee, the most popular beverage worldwide, induces staining and erosion on teeth. We show the grade of erosion of molars and incisors in Sprague Dawley rats from two different age groups, young (four weeks) and old (six months). We quantified the concentration of metals contained in coffee by mass spectrometry (ICP-MS). To determine elemental content in enamel (i.e. superficial) and dentin (i.e. substructure), we used Laser-induced Breakdown Spectroscopy (LIBS) and X-ray fluorescence (XRF) spectroscopy, respectively. For LIBS, a significant decrease of Ca, P, and Na was observed in the young coffee group relative to age-matched controls, whereas a significant increase in Mn, Fe, and K was observed. In the old coffee group, a significant increase of Mg, Fe, and K was observed along with a decrease of Mg, Ca, P, Na, Sr and Zn. For XRF, a significant decrease of the Ca/P ratio in the coffee group was observed. Spectroscopy results were correlated with scanning electron microscopy (SEM) and histological analysis. The SEM analysis showed pores and open spaces between young and old coffee groups, respectively. Thinning of enamel layers, loss of continuity in the enamel-dentin-junction, and wide spaces in dentin tubules with coffee use was found histologically. Coffee induces decalcification of teeth that corresponds to erosion, exposing the dentin structure by reducing enamel. Coffee immersion demonstrated an intrinsic staining in dentin by metal deposition.

General monogamy equalities of complementarity relation and distributive entanglement for multi-qubit pure states

We propose a method to detect genuine quantum correlation for multi-qubit pure states. We then derive a complementarity relations for pure quantum states of N qubits. We prove that in all many-qubit systems there exist strict monogamy laws for quantum correlations. On the other hand, it is known that the entanglement monogamy equality proposed by Coffman, Kundu, and Wootters is in general not true for multiqubit states. Inducing from the CKW equality, we find a proper form of entanglement monogamy equality for arbitrary quantum states. The total quantum correlation of qubit k with the remaining qubits Rk can be characterizes. Furthermore, the quantum correlation of qubit mn with the remaining qubits Rmn can also be obtained. Furthermore, some monogamy relations have been obtained.

Spontaneous parametric four wave mixing and fluorescence lifetime manipulation in the diamond nitrogen vacancy center

We report the lifetime of spontaneous parametric four wave mixing (SP-FWM) and multiorder fluorescence in two-, three-, and four-level systems of negatively charged nitrogen vacancy (NV−) in diamond. The lifetime of SP-FWM is enhanced at high power by the induced dark state from coupling fields. The reduction and enhancement in fluorescence lifetime are attributed to destructive and constructive quantum interference, respectively. The quantum interference is induced by interaction among different decay pathways of spontaneous emission by closely spaced energy levels, which can be controlled by dipole–dipole interaction and the mutual orientations of dipole moments. The lifetime is observed to be longer in two-level as compared to three-level and four-level systems. The different measured lifetimes suggest the sensitivity of these NV systems to quantum interference and the dressing effect. These outcomes may provide new insights in development of all-optical communication devices and quantum storage on photonic chips.

Amplifier and Router of Parametric Amplified Four-Wave Mixing

We investigated an optical amplifier and router by the aperture nonlinear phase and the phase angle of parametric amplified four-wave mixing in a thermal rubidium vapor. The three-stage optical amplifier has been realized and the total amplified gain is observed up to 10. The router action results from the multi-peaks (multi-pair two-modes) while the cross talk of router can be realized by the opposite dressing shift of composite Autler-Townes splitting.

Rapid and in situ optical detection of trace lithium in tissue

Lithium-based medications are used against many mental disorders, including Bipolar disorder and Alzheimer’s disease. However, lithium’s distribution in organs and cells is poorly characterized due to limitations in detection. This limits the ability to improve lithium-based treatments. To address this need, laser induced breakdown spectroscopy (LIBS) is developed for rapid and in situ detection of lithium in tissues. Pronounced lithium emissions are observed at 670.7 nm from the rat thyroid and salivary glands. The lithium emission intensity is positively correlated with tissue lithium concentration (R2=0.80). When subjects are administered lithium orally, thyroid lithium intensity increases (p<0.05) while iodine intensity decreases (p<0.001). The reduced intrathyroidal iodine following administration likely impairs hormone production. This reduced intrathyroidal iodine is also observed when iodine is supplemented on the regular diet, which agrees with the hypothesis of Wolff–Chaikoff.

Detection of lithium in breast milk and in situ elemental analysis of the mammary gland

Breast feeding provides considerable benefits to the infant and mother. However, a lithium-based psychiatric medication may cause side effects in the child. Using laser induced breakdown spectroscopy (LIBS), trace lithium levels were observed in the breast milk of lactating rats administered with lithium treatment postpartum. Subsequently, the mammary glands of female rats were analyzed using LIBS, energy dispersive X-ray fluorescence spectroscopy, and inductively coupled plasma mass spectrometry. Key biological elements iron, magnesium, cobalt, calcium, phosphorus, sodium, iodine, potassium, sulfur, chlorine and zinc were observed. Lithium at 1.06 µg/g was measured in the mammary glands of treated subjects, but was below the limit of detection in controls. Lithium also increased iodine content in the glands. Lithium is present in the breast milk and mammary glands of lithium treated female subjects and this is the likely route of entry to breast-fed infants.