Intrinsic dichroism in amorphous and crystalline solids with helical light.

Amorphous solids do not exhibit long-range order due to the disordered arrangement of atoms. They lack translational and rotational symmetry on a macroscopic scale and are therefore isotropic. As a result, differential absorption of polarized light, called dichroism, is not known to exist in amorphous solids. Using helical light beams that carry orbital angular momentum as a probe, we demonstrate that dichroism is intrinsic to both amorphous and crystalline solids. We show that in the nonlinear regime, helical dichroism is responsive to the short-range order and its origin is explained in terms of interband multiphoton assisted tunneling. We also demonstrate that the helical dichroism signal is sensitive to chirality and its strength can be controlled and tuned using a superposition of OAM and Gaussian beams. Our research challenges the conventional knowledge that dichroism does not exist in amorphous solids and enables to manipulate the optical properties of solids.

Helical dichroism in enantiomeric solutions.

A novel chiroptical sensing technique was recently introduced that utilized the helical phase of the structured light as a chiral reagent instead of polarization of light to differentiate enantiopure chiral liquids. The unique advantage of this non-resonant, nonlinear technique is that the chiral signal can be scaled and tuned. In this paper, we extend this technique to enantiopure powders of alanine and camphor by dissolving them in solvents of varying concentrations. We show the differential absorbance of helical light to be an order of magnitude higher relative to conventional resonant linear techniques and is comparable to nonlinear techniques that use circularly polarized light. The origin of helicity dependent absorption is discussed in terms of induced multipole moments in nonlinear light-matter interaction. These results opens up new opportunities in using helical light as a primary chiral reagent in nonlinear spectroscopic techniques.

Progressive Familial Intrahepatic Cholestasis: A Study in Children From a Liver Transplant Center in India.

Background/Aims: This study aimed to delineate the clinical profile of children diagnosed with progressive familial intrahepatic cholestasis (PFIC). Methods: This study was a retrospective analysis of case records of children in the tertiary care hospital, with the diagnosis of PFIC from January 2017 to January 2020. The diagnosis was made using clinical and laboratory parameters and with genetic testing when available. Medical and surgical management was according to the departmental protocol. Liver transplant was offered to children with end-stage liver disease, intractable pruritus, or severe growth failure. Result: There were 13 identified PFIC cases (familial intrahepatic cholestasis 1 [FIC1] deficiency-4, bile salt export pump (BSEP) deficiency-3, tight junction protein [TJP2] deficiency 3, multidrug-resistant protein 3 [MDR3] deficiency 2 and farnesoid X receptor deficiency-1). PFIC subtypes 1, 2, and 5 presented in infancy, whereas MDR3 presented in childhood. TJP2 deficiency had varied age of presentation from infancy to adolescence. Jaundice with or without pruritus was present in most cases. Genetic testing was carried out in 10 children, of which five had a homozygous mutation, three had a compound heterozygous mutation, and two had a heterozygous mutation. Three children (FIC1-2 and TJP2-1) underwent biliary diversion, of which clinical improvement was seen in two. Six children underwent liver transplantation, which was successful in four. Conclusion: Byler's disease was the most common subtype. A clinicopathologic correlation with molecular diagnosis leads to early diagnosis and management. Liver transplantation provides good outcomes in children with end-stage liver disease.

Chiral discrimination by recollision enhanced femtosecond laser mass spectrometry.

Chiral molecules and their interactions are critical in a variety of chemical and biological processes. Circular dichroism (CD) is the most widely used optical technique to study chirality, often performed in a solution phase. However, CD has low-efficiency on the order of 0.01-1[Formula: see text]. Therefore, there is a growing need to develop high-efficiency chiroptical techniques, especially in gas-phase, to gain background-free in-depth insight into chiral interactions. By using mass spectrometry and strong-field ionization of limonene with elliptically polarized light, we demonstrate an efficient chiral discrimination method that produces a chiral signal of one to two orders of magnitude higher than the conventional CD. The chiral response exhibits a strong dependence on wavelength in the range of 1,300-2,400 nm, where the relative abundance of the ion yields alternates between the two enantiomers. The origin of enhanced enantio-sensitivity in intense laser fields is attributed to two mechanisms that rely on the recollision dynamics in a chiral system: (1) the excited ionic state dynamics mediated either by the laser field or by the recollision process, and (2) non-dipole effects that alter the electron's trajectories. Our results can serve as a benchmark for testing and developing theoretical tools involving non-dipole effects in strong-field ionization of molecules.

Author Correction: Femtosecond Laser Mass Spectrometry and High Harmonic Spectroscopy of Xylene Isomers.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

Femtosecond Laser Mass Spectrometry and High Harmonic Spectroscopy of Xylene Isomers.

Structural isomers, molecules having the same chemical formula but with atoms bonded in different order, are hard to identify using conventional spectroscopy and mass spectrometry. They exhibit virtually indistinguishable mass spectra when ionized by electrons. Laser mass spectrometry based on photoionization of the isomers has emerged as a promising alternative but requires shaped ultrafast laser pulses. Here we use transform limited femtosecond pulses to distinguish the isomers using two methods. First, we probe doubly charged parent ions with circularly polarized light. We show that the yield of doubly charged ortho-xylene decreases while para-xylene increases over a range of laser intensities when the laser polarization is changed from linear to circular. Second, we probe high harmonic generation from randomly oriented isomer molecules subjected to an intense laser field. We show that the yield of high-order harmonics varies with the positioning of the methyl group in xylene isomers (ortho-, para- and meta-) and is due to differences in the strength of tunnel ionization and the overlap between the angular peaks of ionization and photo-recombination.

Ultra-high density optical data storage in common transparent plastics.

The ever-increasing demand for high data storage capacity has spurred research on development of innovative technologies and new storage materials. Conventional GByte optical discs (DVDs and Bluray) can be transformed into ultrahigh capacity storage media by encoding multi-level and multiplexed information within the three dimensional volume of a recording medium. However, in most cases the recording medium had to be photosensitive requiring doping with photochromic molecules or nanoparticles in a multilayer stack or in the bulk material. Here, we show high-density data storage in commonly available plastics without any special material preparation. A pulsed laser was used to record data in micron-sized modified regions. Upon excitation by the read laser, each modified region emits fluorescence whose intensity represents 32 grey levels corresponding to 5 bits. We demonstrate up to 20 layers of embedded data. Adjusting the read laser power and detector sensitivity storage capacities up to 0.2 TBytes can be achieved in a standard 120 mm disc.

Femtosecond laser induced surface swelling in poly-methyl methacrylate.

We show that surface swelling is the first step in the interaction of a single femtosecond laser pulse with PMMA. This is followed by perforation of the swollen structure and material ejection. The size of the swelling and the perforated hole increases with pulse energy. After certain energy the swelling disappears and the interaction is dominated by the ablated hole. This behaviour is independent of laser polarization. The threshold energy at which the hole size coincides with size of swelling is 1.5 times that of the threshold for surface swelling. 2D molecular dynamics simulations show surface swelling at low pulse energies along with void formation below the surface within the interaction region. Simulations show that at higher energies, the voids coalesce and grow, and the interaction is dominated by material ejection.

Fabrication of microlens arrays in polycarbonate with nanojoule energy femtosecond laser pulses.

We report fabrication of smooth microlens arrays by focusing a nanojoule energy, high repetition rate femtosecond laser oscillator inside a polycarbonate sample. Heat accumulation at the laser focal point and subsequent material expansion leads to localized swelling at the sample surface that behaves as a microlens. By changing the depth of the laser focus in the sample, the focal length of the microlens can be controlled and varies from 40 to 80 µm while maintaining a high numerical aperture of ~0.6. This fabrication technique is a single step, controllable, and economical process that can produce arrays of optically smooth microlenses.

Mechanism for spherical dome and microvoid formation in polycarbonate using nanojoule femtosecond laser pulses.

Spherical domes are created on the surface of polycarbonate samples, and microvoids are formed within the bulk using only a femtosecond oscillator with pulse energy of just 0.47 nJ. Size of spherical domes and shape of microvoids are controlled by changing the laser focus inside the material. Their formation is explained by a combination of heat accumulation and dome formation dynamics, where the dome acts as a microlens shifting the laser focus within the sample. The technique described here provides a simple avenue for fabricating smooth microlens arrays of various sizes and opens the possibility for direct fabrication of complex three-dimensional microfluidic channels in transparent materials.

Impact of fly ash composition on mercury speciation in simulated flue gas.

The impact of different fly ash samples on mercury speciation in simulated flue gas at 140 degrees C was evaluated in this study. Experiments were conducted in a fixed bed reactor to determine the impact of fly ash morphological characteristics and chemical composition on mercury uptake and oxidation. No homogeneous mercury oxidation was observed at 140 degrees C. Mercury uptake tests with different fly ash samples revealed that loss on ignition (LOI), surface area, and particle size all had positive effects on mercury oxidation and adsorption (i.e., as the above parameters increased, mercury adsorption and oxidation also increased). Experiments with pure inorganic components showed that alumina (A12O3), silica (SiO2), calcium oxide (CaO), magnesium oxide (MgO), and titania (TiO2) do not promote mercury oxidation or adsorption. Ferric oxide (Fe2O3) and unburned carbon, on the other hand, showed significant mercury oxidation and capture.