Robert Lingle

Ultrafast transient Raman investigation of geminate recombination and vibrational energy relaxation in iodine: The role of energy relaxation pathways to solvent vibrations

Direct observation of geminate recombination and vibrational energy relaxation in the X state of iodine has been accomplished using picosecond Raman spectroscopy. The dynamics of energy relaxation from vibrational levels ranging from v=52 to v=1 have been observed. These levels correspond to absolute energies of 9300 to 210 cm−1 above the zero point in the X potential. The effect of relaxation to solvent vibrations in resonance with I2 vibrations has been studied. The efficiency of these vibrational–vibrational relaxation channels is found to be very solvent dependent. The results suggest that the vibrational coupling between the excited iodine oscillator and the solvent is drastically affected by the nature of the normal mode character of the solvent vibration.

Ultrafast investigation of condensed phase chemical reaction dynamics using transient vibrational spectroscopy: Geminate recombination, vibrational energy relaxation, and electronic decay of the iodine A’ excited state

The reaction dynamics of iodine geminate recombination on the excited A’u20093Π2u state are investigated using picosecond transient Raman spectroscopy. Vibrational energy relaxation and the dynamics of geminate recombination are directly observed in the transient Raman spectrum. Geminate recombination rates are significantly slower for the excited electronic state compared to the ground electronic state. This observation implies that a fundamentally different geminate recombination mechanism is responsible for the formation of the A’u20093Π2u state. Evidence is reported which suggests the possible role of iodine atom–solvent complexes in the reaction step leading from photodissociated atoms to formation of the excited state. The solvent dependence of vibrational energy relaxation suggests that the rate is dominated by V–T (and possibly V–R) energy relaxation which is also found to be significantly slower in the excited electronic state compared to the ground state. In n‐hexane the vibrational relaxation rate appe...

Direct measurement of solvent cage dynamics following photodissociation of iodine using picosecond Raman spectroscopy

Photodissociation of iodine in CCl4 at 532 nm deposits 6300 cm−1 of energy into the solvent cage immediately surrounding the solute. Picosecond Raman spectroscopy has been used to investigate the dissipation of this energy in the solvent coordinate by monitoring time‐dependent shifts in the Raman lineshapes of the local solvent cage.

Few-Mode Fiber Technology for Spatial Multiplexing

This chapter gives an overview of design and optimization of few-mode optical fibers (FMF) for space-division multiplexed transmission. The design criteria are outlined, along with performance limitations of the traditional step-profile and graded-index profiles. The trade-offs between number of usable optical modes (related to total channel capacity), differential group delay, differential mode attenuation, mode coupling, and the impact on MIMO (multiple-input and multiple-output) receiver complexity are outlined. Improved fiber designs are analyzed which maximize channel capacity with foreseeable next-generation receiver technology. FMF measurement technology is overviewed.

Direct measurement of photodissociation, geminate recombination, and vibrational cooling in iodine using picosecond Raman spectroscopy

The photodissociation and geminate recombination of iodine in cyclohexane has been studied by directly monitoring the vibrational coordinates using transient Raman spectroscopy. Energy relaxation as a function of vibrational energy gap has been measured for vibrational spacings of 210 to 130 cm−1. These vibrational levels correspond approximately to v=3 to v=52 with energies 740 to 9300 cm−1 above the zero point level. The results support earlier experiments in that over 100 ps is required to completely relax the vibrational energy.

Advanced multimode fiber for high-speed short-reach interconnect

In this paper, we describe the characteristics of advanced MMF, how it is specified, how it is manufactured, and update its application in IEEE P802.3ba 40G/100G SR4/10 standards development.

Light-Guiding Fundamentals and Fiber Design

This chapter introduces the fundamental concepts of the guidance of light in optical fibers made from dielectric materials, such as silica, with an emphasis on optical transmission properties relevant to communications. Optical fibers are fabricated by first depositing high-purity silica soot, doped with germania to raise the index of refraction or fluorine to lower the index of refraction, to form a core rod of 1 cm or more in diameter and 1 m or more in length. The cutoff wavelength of a single-mode optical fiber is the wavelength above which only a single bound mode, the fundamental linearly polarized (LP) mode, propagates. For numerous reasons concerning transmission performance, it is desirable to operate fibers in the regime where only the fundamental mode propagates. An optical fibers dispersion is the tendency for the fiber to either broaden or narrow a pulse as it travels along the fiber. In a single-mode fiber, chromatic dispersion of the fundamental mode is caused by the dispersive properties of the materials that the fiber is made from, referred to as material dispersion, as well as by the dispersive properties of the waveguide, referred to as waveguide dispersion.

Guided Acoustic-Wave Brillouin Scattering in Few-Mode Fibers

We measured the guided acoustic-wave Brillouin scattering in a few-mode fiber that supports LP01 and LP11 modes. We observed a strong correlation between the acoustic modes and optical intramodal and intermodal Brillouin scattering.

Specialty high bandwidth multimode fiber for optical interconnection

In this paper, we review special high bandwidth multimode fiber and their role in upgrade path of optical interconnection to 40Gbps and 100Gbps in green data centers and high performance computing.

Probing the reaction coordinate for ligand binding in hemoglobin using ultrafast transient Raman spectroscopy

Transient picosecond Raman spectroscopy is capable of differentiating vibrational relaxation from conformational changes by comparing the Stokes and anti-Stokes dynamics. We report pump-probe picosecond Raman experiments on oxy- and deoxyhemoglobin (oxyHb and deoxyHb, respectively) using 8 ps 532 nm pump pulses and 8 ps 355 nm probe pulses. Heme- to-protein vibrational cooling has been directly observed in deoxyHb for the first time, and the deconvolved cooling time constant is measured to be 2 - 5 ps. By applying our mode-specific Stokes and anti-Stokes technique to oxyHb, we find that any geminate recombination of photodeligated O2 must occur in either less than two picoseconds or longer than a nanosecond.