John M. Girkin

Bio: John M. Girkin is an academic researcher from Durham University. The author has contributed to research in topics: Adaptive optics & Microscopy. The author has an hindex of 35, co-authored 215 publications receiving 4070 citations. Previous affiliations of John M. Girkin include University of Southampton & University of Glasgow.

Practical implementation of adaptive optics in multiphoton microscopy

Abstract: A dedicated two-photon microscope incorporating adaptive-optic correction of specimen-induced aberrations is presented. Wavefront alteration of the scanning laser beam was achieved by use of a micromachined deformable mirror. Post scan head implementation produces a compact module compatible with the Bio-Rad MRC-600 scan head. Automatic aberration correction using feedback from the multiphoton fluorescence intensity allowed the adaptive optic to extend the imaging depth attainable in both artificial and biological refractive-index mismatched samples. With a 1.3-NA, x40, Nikon oil immersion objective, the imaging depth in water was extended from approximately 3.4 to 46.2 µm with a resolution defined by a FWHM axial point-spread function of 1.25 µm.

Optical ferris wheel for ultracold atoms

Abstract: We propose a versatile optical ring lattice suitable for trapping cold and quantum degenerate atomic samples. We demonstrate the realisation of intensity patterns from pairs of Laguerre-Gauss (exp(ilθ)) modes with different l indices. These patterns can be rotated by introducing a frequency shift between the modes. We can generate bright ring lattices for trapping atoms in red-detuned light, and dark ring lattices suitable for trapping atoms with minimal heating in the optical vortices of blue-detuned light. The lattice sites can be joined to form a uniform ring trap, making it ideal for studying persistent currents and the Mott insulator transition in a ring geometry.

A Review of Potential New Diagnostic Modalities for Caries Lesions

Abstract: This paper aims to present a simple overview of potential new diagnostic methods for dental caries There are several novel methods of caries detection (with potential application to diagnosis) which have been proposed in the last few years, in addition to those that are gaining some commercial exposure and clinical acceptance For the most part, these methods have been demonstrated in laboratories and are generally many years away from routine clinical application They include multi-photon imaging, infrared thermography and infrared fluorescence, optical coherence tomography, ultrasound, and terahertz imaging

GaN micro-light-emitting diode arrays with monolithically integrated sapphire microlenses

Abstract: GaN micro-light-emitting diodes (micro-LEDs) with monolithically integrated microlenses have been demonstrated. Microlenses, with a focal length of 44 μm and a root mean square roughness of ∼1 nm, have been fabricated on the polished back surface of a sapphire substrate of an array of micro-LEDs by resist thermal reflow and plasma etching. The optical properties of the microlenses have been demonstrated to alter the emission pattern of the LED emitters. The cone of light emitted from this hybrid device is significantly less divergent than a conventional broad-area device. This combination of micro-LED and microlens technologies offers the potential for further improvement in the overall efficiency of GaN-based light emitters.

Adaptive optics for enhanced signal in CARS microscopy.

Abstract: We report the use of adaptive optics with coherent anti-Stokes Raman scattering (CARS) microscopy for label-free deep tissue imaging based on molecular vibrational spectroscopy. The setup employs a deformable membrane mirror and a random search optimization algorithm to improve signal intensity and image quality at large sample depths. We demonstrate the ability to correct for both system and sample-induced aberrations in test samples as well as in muscle tissue in order to enhance the CARS signal. The combined system and sample-induced aberration correction increased the signal by an average factor of ~3x for the test samples at a depth of 700 µm and ~6x for muscle tissue at a depth of 260 µm. The enhanced signal and higher penetration depth offered by adaptive optics will augment CARS microscopy as an in vivo and in situ biomedical imaging modality.

Nonlinear magic: multiphoton microscopy in the biosciences

Abstract: Multiphoton microscopy (MPM) has found a niche in the world of biological imaging as the best noninvasive means of fluorescence microscopy in tissue explants and living animals. Coupled with transgenic mouse models of disease and 'smart' genetically encoded fluorescent indicators, its use is now increasing exponentially. Properly applied, it is capable of measuring calcium transients 500 microm deep in a mouse brain, or quantifying blood flow by imaging shadows of blood cells as they race through capillaries. With the multitude of possibilities afforded by variations of nonlinear optics and localized photochemistry, it is possible to image collagen fibrils directly within tissue through nonlinear scattering, or release caged compounds in sub-femtoliter volumes.

Bose-Einstein condensation in a gas of sodium atoms

Abstract: Bose-Einstein condensation (BEC) has been observed in a dilute gas of sodium atoms. A Bose-Einstein condensate consists of a macroscopic population of the ground state of the system, and is a coherent state of matter. In an ideal gas, this phase transition is purely quantum-statistical. The study of BEC in weakly interacting systems which can be controlled and observed with precision holds the promise of revealing new macroscopic quantum phenomena that can be understood from first principles.

CODATA Recommended Values of the Fundamental Physical Constants: 2006

Abstract: This paper gives the 2010 self-consistent set of values of the basic constants and conversion factors of physics and chemistry recommended by the Committee on Data for Science and Technology (CODATA) for international use. The 2010 adjustment takes into account the data considered in the 2006 adjustment as well as the data that became available from 1 January 2007, after the closing date of that adjustment, until 31 December 2010, the closing date of the new adjustment. Further, it describes in detail the adjustment of the values of the constants, including the selection of the final set of input data based on the results of least-squares analyses. The 2010 set replaces the previously recommended 2006 CODATA set and may also be found on the World Wide Web at physics.nist.gov/constants.

Orbital angular momentum: origins, behavior and applications

Abstract: As they travel through space, some light beams rotate. Such light beams have angular momentum. There are two particularly important ways in which a light beam can rotate: if every polarization vector rotates, the light has spin; if the phase structure rotates, the light has orbital angular momentum (OAM), which can be many times greater than the spin. Only in the past 20 years has it been realized that beams carrying OAM, which have an optical vortex along the axis, can be easily made in the laboratory. These light beams are able to spin microscopic objects, give rise to rotational frequency shifts, create new forms of imaging systems, and behave within nonlinear material to give new insights into quantum optics.