Knowledge Base

Photorefractive Holographic Gratings

Characterization of PDLC holographic gratings

In this paper we present the results of an experimental study of the diffractive properties of electrically switched holographic gratings fabricated using polymer-dispersed liquid crystal mixtures. These composite gratings can be used to fabricate high contrast, electrically switchable, diffractive elements for the visible and near infrared region of the spectrum for optical switching and beam steering applications

Controlling the anisotropy of holographic polymer-dispersed liquid-crystal gratings

In this work we investigate the optical properties of electrically switched transmission gratings fabricated holographically using polymer-dispersed liquid-crystal (PDLC) materials. We have found that the PDLC mixture can be used to control the diffractive properties of the liquid-crystal composite gratings. In one limit the gratings are highly isotropic and in the other limit the gratings are highly anisotropic with a large birefringence. The experimental results are compared to theories that include the birefringence of the grating. From theoretical fits to the experimental data, measurements of the liquid-crystal distribution and alignment are obtained.

Key words:

Photoretractive and Photromic Polymers and Liquid (CThE), Beam steering, Holographic gratings, Infrared radiation, Light beams, Near infrared radiation, Nematic liquid crystals, statistical nonlinear, soft matter physics

Atomic Molecular Optical (AMO) Physics

Isotopic difference in the heteronuclear loss rate in a two-species surface trap

We have realized a two-species mirror-magneto-optical trap containing a mixture of 87Rb(85Rb) and 133Cs atoms. Using this trap, we have measured the heteronuclear collisional loss rate β′Rb-Cs due to intraspecies cold collisions. We find a distinct difference in the magnitude and intensity dependence of β′Rb-Cs for the two isotopes 87Rb and 85Rb which we attribute to the different ground-state hyperfine splitting energies of the two isotopes.

On-chip optical detection of laser cooled atoms

We have used an optical fiber-based system to implement optical detection of atoms trapped on a reflective “atom-chip”. A fiber pair forms an emitter-detector setup that is bonded to the atom-chip surface to optically detect and probe laser cooled atoms trapped in a surface magneto-optical trap. We demonstrate the utility of this scheme by measuring the linewidth of the Cs D2 line at different laser intensities

Creating, detecting and locating ultracold molecules in a surface trap

Ultracold molecules have been produced by photoassociation of Cs atoms trapped in a mirror magneto-optical trap. The molecules were detected by resonantly enhanced multi-photon ionization followed by time-of-flight mass spectroscopy. The time-of-flight of atomic and molecular ions was investigated in the presence of a dc bias voltage applied to the conducting mirror. This technique provides a new tool for determining the distance between the cold molecules and the mirror surface.

Key Words:

Optical, Trapping, Cooling and Detection, Fiber optics sensors; Laser cooling; Absorption; Spectroscopy, Atomic, Molecular, and Optical physics (AMO) and quantum information

Two-Photon Microscopy

Compensation-free, all-fiber-optic, two-photon endomicroscopy at 1.55 μm

We present an all-fiber-optic scanning multiphoton endomicroscope with 1.55 μm excitation without the need for prechirping femtosecond pulses before the endomicroscope. The system consists of a 1.55 μm femtosecond fiber laser, a customized double-clad fiber for light delivery and fluorescence collection, and a piezoelectric scan head. We demonstrate two-photon imaging of cultured cells and mouse tissue, both labeled with indocyanine green. Free-space multiphoton imaging with near-IR emission has previously shown benefits in reduced background fluorescence and lower attenuation for the fluorescence emission. For fiber-optic multiphoton imaging there is the additional advantage of using the soliton effect at the telecommunication wavelengths (1.3–1.6 μm) in fibers, permitting dispersion-compensation-free, small-footprint systems. We expect these advantages will help transition multiphoton endomicroscopy to the clinic.

Integrated multimodal endomicroscopy platform for simultaneous en face optical coherence and two-photon fluorescence imaging

We report an all-fiber-optic scanning, multimodal endomicroscope capable of simultaneous optical coherence tomography (OCT) and two-photon fluorescence (TPF) imaging. Both imaging modalities share the same miniature fiber-optic scanning endomicroscope, which consists of a double-clad fiber with a core operating in single mode at both the OCT (1310 nm) and two-photon excitation (1550 nm) wavelengths, a piezoelectric two-dimensional fiber-optic beam scanner, and a miniature aspherical compound lens suitable for simultaneous acquisition of en face OCT and TPF images. A fiber-optic wavelength division multiplexer was employed in the integrated platform to combine the low coherence OCT light source and the femtosecond two-photon excitation laser into the same optical path. Preliminary imaging results of cell cultures and mouse tissue ex vivo demonstrate the feasibility of simultaneous real-time OCT and TPF imaging in a scanning endomicroscopy setting for the first time.

Nonlinear Optics

Slow Light - Moving Out of the Lab

When put into practical use, slow-light-enhanced technologies will improve the performance of photonic networks and optical sensors. Photonic crystals will play a key role in the transition, as they hold promise for integration into nanophotonic circuits.

Cryo-Raman Spectroscopy

Low vibration high numerical aperture automated variable temperature Raman microscope*

Figure Legend: (a) Cross section of the Cryo-Optic module with Zeiss objective inside the Cryostation housing, highlighting critical components. (b) Bottom view of the objective housing showing a 1 mm beryllium copper aperture in detail from the point-of-view of the ATSM sample platform. The objective housing is thermally coupled to the 60 K sample radiation shield through a bolted interface.

Key Words

Phase transitions, Phonons, Raman scattering, Raman spectroscopy, Raman microspectroscopy, Fiber optics, Optical devices

Multimodal Microscopy

Next-Generation Laser Scanning Multiphoton Microscopes are Turnkey, Portable, and Industry-Ready

The Prospective Instruments MPX-series is a turnkey compact multimodal microscope enabling advanced multiphoton imaging without requiring a laboratory or optical bench. One of the key design features is the ultrafast fiber laser engine integrated into the free moving scan head, which is lightweight, rugged, and allows the ultimate imaging flexibility. A modular design concept allows the user to explore a wide variety of biological applications and measurements, without compromising performance, in any indoor working space. In contrast, standard setups are non-transportable, utility-demanding, and the complexity can be complicated, therefore degrading the value and adding significant initial, short- and long-term expenses. Every clinical and biological researcher should have access to high-quality reliable optical microscopy modalities without being hardware experts. In this article we outline the demand and design of the MPX-microscope and present multiphoton imaging results from experiments in various configurations. There are no existing instruments on the market that are portable and combine easily switchable modes in one composite industry-ready device for life science, clinical, and pharmacological research.

A Multiphoton Microscope Enables Portable 3D Biological Imaging

For decades, optical microscopy has provided the mechanism with which to image cells and tissue for the purposes of cancer research, digital pathology, and the study of the brain. Samples are typically studied in frozen sections. Most of these systems use confocal microscopy and single-photon excitation, typically from a continuous wave light source, to probe the sample. Multiphoton microscopy is used when deep-tissue and cellular-level resolution are desired to preserve the image of the tissue in its native environment. In laser scanning multiphoton microscopes, light from an ultrafast laser is tightly focused and scanned across the sample using fast mirrors. An image is created by detecting the fluorescence signal intensity at each point and mapping spatially with the aid of computer software.

Multiphoton Microscopy for Intravital Imaging in Mice

Intravital imaging in mice has significantly expanded our possibilities to study the in-vivo structural and functional relationships in tissue, overcoming many of the limitations that exist with both postmortem and in vitro preparations. In addition, the use of genetically modified mouse models and targeted labeling techniques allows the study of specific cell types, pathways, or disease-related processes. Advanced imaging techniques like multimodal multiphoton microscopy help to unravel fundamental relationships and researchers to explore tissues with unprecedented detail and precision.

Key words

Biophotonics, Multiphoton microscopy, Multimodal microscopy, Epi-fluorescence, Label-free imaging