arXiv subjects

Hinduja Bhuvanendran

Publications and source records attributed to Hinduja Bhuvanendran.

3 recordsLinked to original sources

arXiv2026

Field-resolved observation and quantification of the instantaneous Kerr response in semiconductors

The optical Kerr effect, whereby the refractive index of a material changes with light intensity, underpins nonlinear photonics and emerging mid-infrared technologies. Accurate determination of the nonlinear refractive index is therefore essential, yet conventional intensity-based techniques infer the nonlinear phase shift indirectly from changes in beam propagation or optical spectra. Moreover, methods such as the $z$-scan cannot resolve the temporal evolution of the nonlinear response, making it difficult to distinguish instantaneous Kerr nonlinearities from delayed contributions, including free-carrier effects. Here, we investigate the nonlinear optical response of germanium at $5 μ\mathrm{m}$ using field-resolved degenerate pump-probe spectroscopy. By measuring the transmitted probe electric field as a function of pump-probe delay, we directly retrieve the pump-induced phase shift and its temporal evolution while retaining sensitivity to changes in absorption. We observe cross-phase modulation that follows the pump intensity envelope and vanishes when the pump and probe no longer overlap, consistent with an instantaneous Kerr response. The phase shift scales linearly with pump intensity, yielding a nonlinear refractive index of $n_2=(0.87\pm0.16)\times10^{-17} \mathrm{m}^2/\mathrm{W}$. Our results establish the instantaneous Kerr effect as the dominant contribution to the measured nonlinear phase shift under our experimental conditions and demonstrate field-resolved pump-probe spectroscopy as a direct, time-resolved method for determining the nonlinear refractive index and distinguishing instantaneous from delayed optical responses.

physics.optics↗

arXiv2024

Structural and optical characterization of NiO polycrystalline thin films fabricated by spray-pyrolysis

Nickel (II) oxide, NiO, a wide band gap Mott insulator characterized by strong Coulomb repulsion between d-electrons and displaying antiferromagnetic order at room temperature, has gained attention in recent years as a very promising candidate for applications in a broad set of areas, including chemistry and metallurgy to spintronics and energy harvesting. Here, we report on the synthesis of polycrystalline NiO fabricated using spray-pyrolysis technique, which is a deposition technique able to produce quite uniform films of pure and crystalline materials without the need of high vacuum or inert atmospheres. We then characterized the composition and structure of our NiO thin films using X-ray diffraction, and atomic force and scanning electron microscopies, respectively. We completed our study by looking at the phononic and magnonic properties of our NiO thin films via Raman spectroscopy, and at the ultrafast electron dynamics by using optical pump probe spectroscopy. We found that our NiO samples display the same phononic and magnonic dispersion expected for single crystal NiO at room temperature, and that electron dynamics in our system is similar to those of previously reported NiO mono- and poli-crystalline systems synthesized with different techniques. These results prove that spray-pyrolysis can be used as affordable and large-scale fabrication technique to synthetize strongly correlated materials for a large set of applications.

cond-mat.mtrl-sci↗

arXiv2023

Generation of ultrashort light pulses carrying orbital angular momentum using a vortex plate retarder-based approach

We use a vortex retarder-based approach to generate few optical cycles light pulses carrying orbital angular momentum (known also as twisted light or optical vortex) from a Yb:KGW oscillator pumping a noncollinear optical parametric amplifier generating sub-10 fs linearly polarized light pulses in the near infrared spectral range (central wavelength 850 nm). We characterize such vortices both spatially and temporally by using astigmatic imaging technique and second harmonic generation-based frequency resolved optical gating, respectively. The generation of optical vortices is analyzed, and its structure reconstructed by estimating the spatio-spectral field and Fourier transforming it into the temporal domain. As a proof of concept, we show that we can also generate sub-20 fs light pulses carrying orbital angular momentum and with arbitrary polarization on the first-order Poincaré sphere.

physics.optics↗