Lyuba Kuznetsova

• PhD
• Professor (Associate) at San Diego State University

We show that nonlinear phase shifts and third-order dispersion can compensate each other in short-pulse fiber amplifiers. In particular, we consider chirped-pulse fiber amplifiers at wavelengths for which the fiber dispersion is normal. The nonlinear phase shift accumulated in the amplifier can be compensated by the third-order dispersion of the co...

By optimizing the cavity dispersion map, 1.5-nJ, 36-fs pulses are obtained from a Yb-doped fiber laser. Higher-order dispersion currently limits the pulse duration.

A Yb fiber laser and amplifier system based entirely on single-mode fiber generates 150-fs pulses with energies up to 0.8 μJ. This source combines high pulse energy with the simplicity and integrability of single-mode fiber.

We demonstrate that the compensation of self-phase modulation by third-order dispersion can be exploited in the design of fiber amplifiers with tens of microjoules pulse energy. At the highest energies, the amplified pulse accumulates nonlinear phase shift as large as 17 π. Gain-narrowing occurs in the final amplifier stage, but shorter pulses are...

A study of chirped-pulse amplification in the presence of large nonlinear phase shifts (as large as ∼ 12 π ) and finite gain bandwidth is presented. Numerical simulations that include the effect of nonlinearity, group-velocity dispersion, higher-order dispersion, and finite gain bandwidth predict the spectral signature of the interplay of nonlinear...

Electrically tunable TiN/SiO2/TiN epsilon-near-zero photonic structures with various parameters were fabricated using the reactive DC magnetron sputtering approach. Effective medium approximation was used to predict the optical permittivity of a multilayered TiN/SiO2 metamaterial and guide the design/fabrication. Experimental reflectance measuremen...

Electrically tunable TiN/SiO 2 /TiN epsilon-near-zero photonic structures were fabricated using DC magnetron sputtering. Reflectance spectra in visible/near-IR for bulk and multilayered TiN/SiO 2 /TiN structures with optimal parameters exhibit spectral shift at the epsilon-near-zero spectral point up to ~10 nm due to applied voltage (12 V).

Ultrashort pulse propagation at the epsilon-near-zero spectral point is numerically investigated using the finite difference time-domain technique for the pump-probe experiment. Free carriers’ population dynamics in the conduction band for large intensities of the pump pulse and the transient response for rapidly varying pulses in two-level media a...

A novel approach to the application of an adaptive pre-shaping algorithm for ultrashort pulse distortion compensation during the propagation in AZO/ZnO multilayered metamaterials (thickness 300-700 nm) at the epsilon-near-zero spectral point is investigated. We show that using the Broyden-Fletcher-Goldfarb-Shanno algorithm to minimize the residual...

Numerical results, using the auxiliary differential equation FDTD method, show that presence of pump pulses (100-500 fs) with various amplitudes results in the dramatic change of probe pulse shape and amplitude in AZO/ZnO metamaterial.

Numerical FDTD study shows that initial 100 fs Gaussian pulse with central frequency beyond epsilon-near-zero point experiences spectral self-tuning during propagation in Al:ZnO/ZnO. The resulting spectral shift depends strongly on optical loss. © 2019 OCIS codes: 070.7345, 160.3918, 320.0320. 1. Introduction The recent development of the epsilon-n...

We engineer a tunable multilayered aluminum-doped zinc oxide metamaterial with low-loss and high-carrier concentration using the pulsed laser deposition. The results of the scanning probe microscopy study show excellent surface quality with a root mean square roughness value of . The transmission electron microscopy measurements indicate a clear la...

The emission properties of aluminum-doped zinc oxide are numerically investigated. A complete model for photoluminescence, based on the set of rate equations for electron–hole recombination, is used to study the influence of carrier concentration () on visible and ultraviolet (UV) emission. The set of coupled rate equations is solved numerically us...

FDTD numerical simulations show that the use of an adaptive pre-shaping can yield increased electric field strength and improved pulse temporal profile for 100 fs pulse propagated through AZO/ZnO metamaterial at the epsilon-near-zero spectral point.

A numerical study of the ultra-short pulse propagation in the aluminum-doped zinc oxide multi-layered metamaterial at the epsilon-near-zero spectral point is presented. The Drude model for dielectric permittivity and comparison with recent experimental data predict that damping frequency γD has the highest impact on the material losses and results...

Numerical FDTD study of ultrashort (100 fs) pulse propagation shows strong pulse shaping for central frequencies smaller than the epsilon-near-zero (ENZ) point, and soliton-like propagation (up to 500 nm) for central frequencies larger than ENZ.

Three-dimensional finite-element-method numerical simulations are used to investigate a size-dependent sensing technique by observing the effects that a spherical nanoparticle had on the frequency resonances of whispering-gallery modes of a subwavelength silicon microdisk. Results show that the observed spectral shift varies significantly ( ∼ 2 to...

This paper presents the results of a numerical study of the optical mode confinement in whispering gallery mode disk nanocavities with hyperbolic dispersion using nanolayered Al/SiO2 hyperbolic metamaterial with different Al fill fractions. The fundamental properties of the optical modes and resonance frequencies for the disk nanocavities are studi...

A special class of nano-layered hyperbolic metamaterials (HMMs) has received special attention recently due to their unique optical property, namely that the dispersion of the dielectric constant for HMMs exhibits a topological transition in the iso-frequency surface from an ellipsoid to a hyperboloid. Using aluminum in metal-dielectric nano-layere...

Nano-layered Al:ZnO/ZnO hyperbolic dispersion metamaterial with a large number of layers was fabricated using the atomic layer deposition (ALD) technique. Experimental dielectric functions for Al:ZnO/ZnO structures are obtained by an ellipsometry technique in the visible and near-infrared spectral ranges. The theoretical modeling of the Al:ZnO/ZnO...

Motivated by a greater need for increased performance in modern-day technology, this paper shows the results of theoretical calculations for the optical properties of Al/SiO2 nano-layered metamaterial with hyperbolic dispersion. Our main focus is on designing a metamaterial with low losses, since losses might outweigh any increase in speed of photo...

Today’s technological needs are demanding for faster and smaller optical components. Optical microcavities offer a high confinement of electromagnetic field in a small volume, with dimensions comparable to the wavelength of light, which provides a unique system for the enhancement of light-matter interactions on the nanoscale. However, further redu...

Three-dimensional finite-element-method simulations are used to investigate a system consisting of a subwavelength silicon microdisk cavity for the detection of different viruses of the same type. This is done by observing the effects that a spherical nanoparticle had on the frequency resonances of WGMs of the silicon microdisk. Results show that t...

The impact on nanolayered metamaterials with hyperbolic dispersion due to nonlocal effects is investigated. Calculations for Al:ZnO/ZnO and Al/SiO2 metamaterials show strong spectral dependence of dielectric permittivity in visible/near-IR as the number of layers decreases.

This work presents a silicon microcavity based, size-sensitive technique, for detecting the same type of biological nanoparticles. Numerical simulations show significant dependence of the spectral shift on the size of the particle (radius: 30-175nm).

Silicon emission in and out resonant coupling with a high Q optical mode is studied in a microdisk cavity with emissive W-centers. Results show that the W-centers photoluminescence intensity in a silicon microdisk is one order of magnitude higher than that in the substrate. It exhibits a maximum when emission line and cavity mode frequencies are ma...

Strong coupling between silicon emissive G-centers and nanostructured microdisk optical mode is studied. Spectra exhibit characteristic splitting (~0.92 THz) when temperature is tuned to match cavity mode (Q~2500) and emissive center frequencies.

The impact of upper state lifetime and spatial hole burning on pulse shape and stability in actively mode locked QCLs is investigated by numerical simulations. It is shown that an extended upper state lifetime is necessary to achieve stable isolated pulse formation per roundtrip. Spatial hole burning helps to reduce the pulse duration by supporting...

In this study, we report the unequivocal demonstration of midinfrared mode-locked pulses from quantum cascade lasers. The train of short pulses was generated by actively modulating the current and hence the gain of an edge-emitting quantum cascade laser (QCL). Pulses with duration of about 3 ps at full-width-at-half-maxima and energy of 0.5 pJ were...

A theoretical study of active mode-locking in quantum cascade lasers including spatial hole-burning is presented. It is found that spatial hole-burning reduces the pulse duration at the expense of slight pulse instability and strongly structured pulse shapes.

A mode-locking mechanism by active gain modulation is studied numerically and experimentally. The parameter window for the emission of stable pulse trains was found. Pulses as short as 3 ps (~0.5 pJ) were characterized by second-order autocorrelation.

We report direct evidence of active mode-locking of quantum cascade lasers from second-order interferometric autocorrelation measurements with a non-linear quantum well infrared photodetector. A FWHM of 3ps was deduced for the stable train of pulses.

The ultrathin (17 — 25 nm thick) continuous Ni films deposited on K8 glass and ZrO2 substrates are experimentally studied. The degenerate four-photon spectroscopy showed typical resonances in the dependence of the self-diffraction efficiency on the wavelength of pump components. It is shown within the framework of the model of electronic cubic nonl...

We report a numerical and experimental study of chirped-pulse amplification of femtosecond pulses near the gain narrowing limit of Yb-doped fiber. We show that a strongly inhomogeneous lineshape provides a good description of pulse amplification in the linear regime (nonlinear phase shift ΦNL<1). Compensation of second- and third-order dispersion u...

The exploitation of nonlinear phase shifts ( Φ N L ) in chirped-pulse fiber amplifiers has been demonstrated recently. Systematic optimization of the performance of a femtosecond-pulse fiber amplifier in the presence of substantial Φ N L is a challenging multivariable problem. We introduce an approximate theoretical model that is valid as long as t...

The functionality of reflection grisms that compensate dispersion of ultrafast systems such as pulse compressor and materials, is discussed. Material-dispersion compensator such as reflection grisms compensate delay imparted to a pulse by a material with a wavelength-dependent index or a pulse compressor with a wavelength-dependent optical path. A...

Compensation of third-order dispersion using a high-efficiency reflection grism pair is demonstrated for the first time in an all-fiber chirped-pulse amplification system. Transform-limited 120 fs pulses are produced near the Yb gain-narrowing limit.

Amplification in the presence of strong self-phase-modulation (ΦNL~12p), finite gain bandwidth (λFWHM~15 nm) and third-order dispersion is studied numerically and experimentally. Pulses amplified to 30 μJ energy in Yb-doped fiber are dechirped to 240 fs duration.

Spectral shaping in a fiber amplifier with finite gain bandwidth (DeltalambdaFWHM~15nm) and strong self-phase-modulation (PhiNL~12pi) is studied numerically and experimentally. Pulses amplified to 30 muJ energy are dechirped to 250 fs duration.

The compensation of nonlinear phase shifts by dispersion in femtosecond fiber amplifiers is explained. Contrary to previous understanding, a chirped-pulse fiber amplifier with mismatched stretcher and compressor can out-perform a matched system when the pulse acquires a significant nonlinear phase shift.

Spectral shaping in a fiber amplifier in the presence of finite gain bandwidth (15 nm) and large nonlinear phase shifts (up to ~12 phi) is studied numerically and experimentally. Pulses amplified to 30 muJ are dechirped to ~250 fs duration

The mechanism of chirped-pulse amplification performance improvement with interplay of nonlinearity and third-order dispersion is successfully interpreted with a simple theoretical model. One can extract design parameters optimizing the output performance according to the model

An analytic model of chirped-pulse amplification is presented. The model is used to optimize the peak power in fiber chirped-pulse amplification, in which the interplay of nonlinearity and third-order dispersion plays a major role.

We show that nonlinear phase shifts and third-order dispersion can compensate each other in short-pulse fiber amplifiers. This compensation can be exploited in any implementation of chirped-pulse amplification, with stretching and compression accomplished with diffraction gratings, single-mode fiber, microstructure fiber, fiber Bragg gratings, etc....

A Yb fiber laser and amplifier system based entirely on single-mode fiber generates 150-fs pulses with energies up to 0.8 μJ. This source combines high pulse energy with the simplicity and integrability of single-mode fiber.

Recent advances in femtosecond fiber lasers are described. Self-similar evolution of parabolic pulses in a modelocked laser can be exploited to substantially increase the pulse energy and peak power that can be achieved without wave-breaking. Experimentally, pulse energies as high as 10 nJ and peak powers as high as 80 kW are obtained from Yb fiber...

By optimizing the cavity dispersion map, 1.5-nJ pulses as short as 36 fs are obtained from a Yb-doped fiber laser. Residual higher-order dispersion currently limits the pulse duration, and it should be possible to generate pulses as short as 25–30 fs with Yb-doped fiber.

We studied third-harmonic generation (THG) in reflection geometry from porous silicon layers grown on (110) silicon substrates. A significant (more than 10 times) enhancement of the THG efficiency compared to crystalline silicon was found for the samples prepared on highly doped substrate, whereas for the samples grown on low-doped substrate the TH...

Third-harmonic generation (THG) in reflection geometry was studied in nanostructured silicon layers grown by electrochemical porosifying of p-type (110) silicon substrates. An order of magnitude enhancement of the THG efficiency compared to crystalline silicon (c-Si) was observed for the samples prepared on a highly doped substrate, whereas for the...

Porous-silicon (PS) based multilayer periodic structures with photonic bandgaps (PBGs) and PS single layers that have a strong in-plane birefringence are produced by the electrochemical nanostructuring of crystalline silicon wafers of different crystallographic orientations. Calculations and experiments demonstrate the possibility of improving phas...

Electrochemically nanostructured Si films with surface orientation (110) prepared at different current density were investigated by Fourier transform infrared spectroscopy. The spectra exhibit beats of interference fringes arisen from the summation of intensities of ordinary and extraordinary waves which interfere in the film. The investigated film...

Birefringence in porous silicon layers prepared with different etching currents on a (110) substrate is studied by IR Fourier spectroscopy. The spectra exhibit beats in the intensity of transmitted and reflected radiation due to the summation of the intensities of the ordinary and extraordinary waves interfering in the porous layer. An analysis of...

Optical second-harmonic generation is investigated in free-standing (110) porous silicon films having strong in-plane birefringence. Based on the measured values of the refractive indices, the conditions of phase matching are calculated and verified in the experiments on angular and polarization dependences of second-harmonic generation. Filling po...

Ultra-thin continuous Ni films of 5–25 nm thickness on K8 glass and ZrO2 substrates were investigated by two methods of coherent four-photon picosecond (20 ps pulse duration) spectroscopy: the biharmonic pumping technique (BP) and degenerate four-photon spectroscopy (DFPS). Specific resonant features were found in the self-diffraction efficiency as...