There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Ultrafast lasers, which generate optical pulses in the picosecond and femtosecond range, have progressed over the past decade from complicated and specialized laboratory systems to compact, reliable instruments. Semiconductor lasers for optical pumping and fast optical saturable absorbers, based on either semiconductor devices or the optical nonlinear Kerr effect, have dramatically improved these lasers and opened up new frontiers for applications with extremely short temporal resolution (much smaller than 10 fs), extremely high peak optical intensities (greater than 10 TW/cm2) and extremely fast pulse repetition rates (greater than 100 GHz).

Recent developments in compact ultrafast lasers

In complex media such as white paint and biological tissue, light encounters nanoscale refractive-index inhomogeneities that cause multiple scattering. Such scattering is usually seen as an impediment to focusing and imaging. However, scientists have recently used strongly scattering materials to focus, shape and compress waves by controlling the many degrees of freedom in the incident waves. This was first demonstrated in the acoustic and microwave domains using time reversal, and is now being performed in the optical realm using spatial light modulators to address the many thousands of spatial degrees of freedom of light. This approach is being used to investigate phenomena such as optical super-resolution and the time reversal of light, thus opening many new avenues for imaging and focusing in turbid media

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Controlling waves in space and time for imaging and focusing in complex media

Diagnostics and Therapy Guanying Chen,‡,† Indrajit Roy,†,§ Chunhui Yang,*,‡ and Paras N. Prasad*,† †Institute for Lasers, Photonics, and Biophotonics and Department of Chemistry, University at Buffalo, State University of New York, Buffalo, New York 14260, United States ‡School of Chemical Engineering and Technology, Harbin Institute of Technology, Harbin, Heilongjiang 150001, China Department of Chemistry, University of Delhi, Delhi 110007, India

Nanochemistry and Nanomedicine for Nanoparticle-based Diagnostics and Therapy

Semiconductor saturable absorber mirror (SESAM) devices have become a key component of ultrafast passive mode-locked laser sources Here we describe in more detail how the key SESAM parameters such as saturation fluence, modulation depth, and nonsaturable losses are measured with a high accuracy These parameters need to be known and controlled to obtain stable pulse generation for a given laser A high-precision, wide dynamic range setup is required to measure this nonlinear reflectivity of saturable absorbers The challenge to measure a low modulation depth and key measures necessary to obtain an accurate calibration are described in detail The model function for the nonlinear reflectivity is based on a simple two-level travelling wave system We include spatial beam profiles, nonsaturable losses and higher-order absorption, such as two-photon absorption and other induced absorption Guidelines to extract the key parameters from the measured data are given

/pdf/optical-characterization-of-semiconductor-saturable-4k0u1z9qz3.pdf

Optical characterization of semiconductor saturable absorbers

A nonlinear optical plasmonic core-shell nanocavity is demonstrated as an efficient, subwavelength coherent light source through second-harmonic generation. The nonlinear optical plasmonic nanocavity incorporates a noncentrosymmetric medium, which utilizes the entire mode volume for even-order nonlinear optical processes. In previous plasmonic nanocavities, enhancement of such processes was only possible at the interface but symmetry prohibited in the body. We measured an enhancement of over 500 times in the second-harmonic radiation power. Calculations show that an enhancement of over 3500 times is achievable.

/pdf/nonlinear-optical-properties-of-core-shell-nanocavities-for-kc58j3gx15.pdf

Nonlinear optical properties of core-shell nanocavities for enhanced second-harmonic generation.

We demonstrate imaging through a turbid layer by using digital phase conjugation of the second harmonic field radiated from a beacon nanoparticle. We show that the phase-conjugated focus can be displaced from its initial position by illuminating the same region of the turbid layer with an angular offset. An image is obtained by scanning the phase-conjugated focus through the turbid layer in a region around the nanoparticle. We obtain a clear image of the target by measuring the light transmitted through it when scanning the focused beam.

Imaging through turbid layers by scanning the phase conjugated second harmonic radiation from a nanoparticle

We demonstrate focusing coherent light on a nanoparticle through turbid media based on digital optical phase conjugation of second harmonic generation (SHG) field from the nanoparticle. A SHG active nanoparticle inside a turbid medium was excited at the fundamental frequency and emitted SHG field as a point source. The SHG emission was scattered by the turbid medium, and the scattered field was recorded by off-axis digital holography. A phase-conjugated beam was then generated by using a phase-only spatial light modulator and sent back through the turbid medium, which formed a nearly ideal focus on the nanoparticle.

Digital phase conjugation of second harmonic radiation emitted by nanoparticles in turbid media

Luminescent markers play a key role in imaging techniques for life science since they provide a contrast mechanism between signal and background. We describe a new type of marker using second harmonic generation (SHG) from noncentrosymmetric BaTiO_3 nanocrystals. These nanoparticles are attractive due to their stable, non-saturating and coherent signal with a femtosecond-scale response time and broad flexibility in the choice of excitation wavelength. We obtained monodispersed BaTiO_3 nanoparticles in colloidal suspensions by coating the particle surface with amine groups. We characterized the SHG efficiency of 90-nm BaTiO_3 particles experimentally and theoretically. Moreover, we use the coherent SHG signal from BaTiO_3 nanoparticles for three-dimensional (3D) imaging without scanning. We built a harmonic holographic (H^2) microscope which records digital holograms at the second harmonic frequency. For the first time, high-resolution 3D distributions of these SHG markers in mammalian cells are successfully captured and interpreted by the H^2 microscope.

/pdf/three-dimensional-harmonic-holographic-microcopy-using-4b9ki76svf.pdf

Rachel Grange

Papers

Optical characterization of semiconductor saturable absorbers

Nonlinear optical properties of core-shell nanocavities for enhanced second-harmonic generation.

Imaging through turbid layers by scanning the phase conjugated second harmonic radiation from a nanoparticle

Digital phase conjugation of second harmonic radiation emitted by nanoparticles in turbid media

Three-dimensional harmonic holographic microcopy using nanoparticles as probes for cell imaging