Necati Kaya, PhD 
Texas A&M University, Department of Physics and Astronomy, College Station, TX 77843-4242 
Office & Laboratories: MPHY 466, ENPH 104, ENPH B11 
email: necati@physics.tamu.edu 

I have been working with femtosecond laser equipment including oscillators, amplifiers, OPAs, fs-pulse shapers and diagnostic equipment such as CCD cameras, spectrometers, autocorrelators and FROG devices in applications for studies of the interaction of fs pulses with matter and spectroscopy.
Research Interests: Femtosecond Lasers Systems, Laser spectroscopy, Femtosecond beam characterization, Computer Generated Holography (CGH), Ultrashort laser filamentation, White-light generation and control, Above Threshold Ionization (ATI), Molecular alignment of diatomic molecules, Ion Optics and Ion Beam Apparatus (IBA), Fragmentation of Molecules in Intense Laser Fields.
We experimentally studied intense femtosecond pulse filamentation and propagation in water for Bessel-Gaussian beams with different numbers of radial modal lobes. The transverse modes of the incident Bessel-Gaussian beam were created from a Gaussian beam of a Ti:sapphire laser system by usingcomputer generated hologram techniques. We found that filament propagation length increased with increasing number of lobes under the conditions of the same peak intensity, pulse duration, and the size of the central peak of the incident beam, suggesting that the radial modal lobes may serve as an energy reservoir for the filaments formed by the central intensity peak. G. Kaya et. al. AIP Advances, 6, 035001 (2016).

We investigated molecular alignment wakes of femtosecond laser pulses. Evolution of nonadiabatic molecular alignment in nitrogen gas has been measured via its nonlinear interaction effects with a variably delayed probe pulse. The induced rotational wave packet was mapped as a function of the angular difference between polarization directions of femtosecond pump and probe pulses as well as their relative delay and the plot of the variations of the rotational wave packet, i.e. “quantum carpet”, was found to be in good agreement with the calculated angular and temporal dependencies of molecular alignment parameter. N. Kaya, G. Kaya, M. Sayrac, Y. Boran, S. Anumula, J. Strohaber, A. A. Kolomenskii, and H. A. Schuessler, "Probing nonadiabatic molecular alignment by spectral modulation," Opt. Express 24, 2562-2576 (2016)

White-light generation is studied in water using spatially- structured beams of femtosecond radiation. By changing the transverse spatial phase of an initial Gaussian beam with a 1D spatial light modulator to that of an Hermite-Gaussian (HGn,m) mode, we were able to generate beams exhibiting phase discontinuities and steeper intensity gradients. When the spatial phase of an initial Gaussian beam (showing no significant white-light generation) was changed to that of a HG01, or HG11 mode, significant amounts of white-light were produced. Because self-focusing is known to play an important role in white-light generation, the self-focusing lengths of the resulting transverse intensity profiles were used to qualitatively explain this production. Distributions of the laser intensity for beams having step-wise spatial phase variations were modeled using the Fresnel-Kirchhoff integral in the Fresnel approximation. N. Kaya, J. Strohaber, A. A. Kolomenskii, G. Kaya, H. Schroeder and H. A. Schuessler, Optics Express 20, 13337 (2012) 

We investigated the variations in generated white-light when crossing two femtosecond laser beams in a Kerr medium. By changing the relative delay of two interacting intense femtosecond laser pulses, we show that white-light generation can be enhanced or suppressed. With a decrease of the relative delay an enhancement of the white-light output was observed, which at even smaller delays was reverted to a suppression of white-light generation. Under choosen conditions, the level of suppression resulted in a white-light output lower than the initial level corresponding to large delays, when the pulses do not overlap in time. The enhancement of the white-light generation takes place in the pulse that is lagging. We found that the effect of the interaction of the beams depends on their relative orientation of polarization and increases when the polarizations are changed from perpendicular to parallel. The observed effects are explained by noting that at intermediate delays, the perturbations introduced in the path of the lagging beam lead to a shortening of the length of filament formation and enhancement of the white-light generation, whereas at small delays the stronger interaction and mutual rescattering reduces the intensity in the central part of the beams, suppressing filamentation and white-light generation. A. A. Kolomenskii, J. Strohaber, N. Kaya, G. Kaya, A. V. Sokolov, and H. A. Schuessler, "White-light generation control with crossing beams of femtosecond laser pulses," Opt. Express 24, 282-293 (2016)

 We introduce a method for analysis of optical beams by using a folded version of a 2f-2f setup containing spatial phase modulator (SLM). The SLM is proven to be useful in producing diverse “soft apertures” that are difficult or impossible to reproduce mechanically. Phase hologram encoded with phase and amplitude information is used to knife edge the laser modes. Precise phase calibration of the SLM is reported. The measured powers from both mechanical and holographic knife-edge methods are found to be in a good agreement with each other. Important new analytic results are the knife-edge equations for the Hermite-Gaussian and Laguerre-Gaussian modes. In both cases good agreement is found between experiment and theory. Finally, the authors tomographically reconstruct a broadband optical beam in a folded 2f-setup. J. Strohaber, G. Kaya, N. Kaya, N. Hart, A. A. Kolomenskii, G. G. Paulus, and H. A. Schuessler, Optics Express, 19, 14321 (2011)