Darren Kraemer
University of Toronto
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Publication
Featured researches published by Darren Kraemer.
Proceedings of the National Academy of Sciences of the United States of America | 2008
Darren Kraemer; Michael L. Cowan; Alexander Paarmann; Nils Huse; Erik T. J. Nibbering; Thomas Elsaesser; R. J. Dwayne Miller
Two-dimensional infrared photon-echo measurements of the OH stretching vibration in liquid H2O are performed at various temperatures. Spectral diffusion and resonant energy transfer occur on a time scale much shorter than the average hydrogen bond lifetime of ≈1 ps. Room temperature measurements show a loss of frequency and, thus, structural correlations on a 50-fs time scale. Weakly hydrogen-bonded OH stretching oscillators absorbing at high frequencies undergo slower spectral diffusion than strongly bonded oscillators. In the temperature range from 340 to 274 K, the loss in memory slows down with decreasing temperature. At 274 K, frequency correlations in the OH stretch vibration persist beyond ≈200 fs, pointing to a reduction in dephasing by librational excitations. Polarization-resolved pump-probe studies give a resonant intermolecular energy transfer time of 80 fs, which is unaffected by temperature. At low temperature, structural correlations persist longer than the energy transfer time, suggesting a delocalization of OH stretching excitations over several water molecules.
PLOS ONE | 2010
Saeid Amini-Nik; Darren Kraemer; Michael L. Cowan; Keith Gunaratne; Puviindran Nadesan; Benjamin A. Alman; R. J. Dwayne Miller
Lasers have in principle the capability to cut at the level of a single cell, the fundamental limit to minimally invasive procedures and restructuring biological tissues. To date, this limit has not been achieved due to collateral damage on the macroscale that arises from thermal and shock wave induced collateral damage of surrounding tissue. Here, we report on a novel concept using a specifically designed Picosecond IR Laser (PIRL) that selectively energizes water molecules in the tissue to drive ablation or cutting process faster than thermal exchange of energy and shock wave propagation, without plasma formation or ionizing radiation effects. The targeted laser process imparts the least amount of energy in the remaining tissue without any of the deleterious photochemical or photothermal effects that accompanies other laser wavelengths and pulse parameters. Full thickness incisional and excisional wounds were generated in CD1 mice using the Picosecond IR Laser, a conventional surgical laser (DELight Er:YAG) or mechanical surgical tools. Transmission and scanning electron microscopy showed that the PIRL laser produced minimal tissue ablation with less damage of surrounding tissues than wounds formed using the other modalities. The width of scars formed by wounds made by the PIRL laser were half that of the scars produced using either a conventional surgical laser or a scalpel. Aniline blue staining showed higher levels of collagen in the early stage of the wounds produced using the PIRL laser, suggesting that these wounds mature faster. There were more viable cells extracted from skin using the PIRL laser, suggesting less cellular damage. β-catenin and TGF-β signalling, which are activated during the proliferative phase of wound healing, and whose level of activation correlates with the size of wounds was lower in wounds generated by the PIRL system. Wounds created with the PIRL systsem also showed a lower rate of cell proliferation. Direct comparison of wound healing responses to a conventional surgical laser, and standard mechanical instruments shows far less damage and near absence of scar formation by using PIRL laser. This new laser source appears to have achieved the long held promise of lasers in minimally invasive surgery.
Optics Express | 2009
Kresimir Franjic; Michael L. Cowan; Darren Kraemer; R. J. Dwayne Miller
Mechanical and thermodynamic responses of biomaterials after impulsive heat deposition through vibrational excitations (IHDVE) are investigated and discussed. Specifically, we demonstrate highly efficient ablation of healthy tooth enamel using 55 ps infrared laser pulses tuned to the vibrational transition of interstitial water and hydroxyapatite around 2.95 microm. The peak intensity at 13 GW/cm(2) was well below the plasma generation threshold and the applied fluence 0.75 J/cm(2) was significantly smaller than the typical ablation thresholds observed with nanosecond and microsecond pulses from Er:YAG lasers operating at the same wavelength. The ablation was performed without adding any superficial water layer at the enamel surface. The total energy deposited per ablated volume was several times smaller than previously reported for non-resonant ultrafast plasma driven ablation with similar pulse durations. No micro-cracking of the ablated surface was observed with a scanning electron microscope. The highly efficient ablation is attributed to an enhanced photomechanical effect due to ultrafast vibrational relaxation into heat and the scattering of powerful ultrafast acoustic transients with random phases off the mesoscopic heterogeneous tissue structures.
Journal of The Optical Society of America B-optical Physics | 2007
Darren Kraemer; Michael L. Cowan; Renzhong Hua; Kresimir Franjic; R. J. Dwayne Miller
The optical parametric chirped pulse amplication (OPCPA) concept has been extended to the infrared range, providing a new approach, to our knowledge, to high-power femtosecond pulses in the 1.5 μm range. This amplifier is based on 1.05 μm pumping of bulk KTiOAsO4 with broadband phase matching in a noncollinear geometry. The output pulse energy of 1 mJ was generated with 50 nm of bandwidth by 3.8 mJ of pump energy from a 100 ps, 1 kHz Nd:YLF amplified laser. Total gain of 108 was achieved in three stages with 32% conversion of the pump energy in the final amplifier stage. Amplified pulses were compressed to 130 fs with peak intensities of 3.85 GW.
Optics Letters | 2006
Darren Kraemer; Renzhong Hua; Michael L. Cowan; Kresimir Franjic; R. J. Dwayne Miller
Amplification of femtosecond pulses at 1.56 microm based on noncollinear parametric chirped pulse amplification in a potassium titanyl arsenate (KTA) crystal with pumping at 1.05 microm is reported. The 100 fs pulses of an erbium fiber laser are parametrically amplified while synchronously pumped by an amplified mode-locked Nd:YLF laser. This amplifier has a saturated gain of 65 dB with 30% conversion efficiency and has produced 160 fs pulses with peak powers of up to 0.75 GW. The system produced 380 mW before compression and can be readily scaled to the multiwatt range with bandwidths to support sub-100 fs pulses.
Chemical Physics | 2002
Darren Kraemer; Bradley J. Siwick; R. J. Dwayne Miller
A post processing algorithm called matrix-method deconvolution (MMD) was created that makes it possible to extract binary information from optical data storage beyond the limits of the Rayleigh criterion. The method was designed for use with an optical memory system that reads and writes binary information in a nanocomposite material consisting of optically sensitive particles, hexagonally closed packed in an inert matrix. The limiting conditions for error-free superresolution [EFS] of this type were quantified using a computer simulation of the imaging conditions. It is predicted that with MMD, the density of existing optical memory systems could be boosted by at least an order of magnitude.
Archive | 2005
Robert John Dwayne Miller; Kresimir Franjic; Darren Kraemer; Michel Piche
Archive | 2006
Kresimir Franjic; Darren Kraemer; Michael L. Cowan; Renzhong Hua; Robert John Dwayne Miller
Archive | 2001
Darren Kraemer; Bradley J. Siwick; R. J. Dwayne Miller
Archive | 2017
Darren Kraemer; Michael L. Cowan