arXiv subjects

Ajinkya Punjal

Publications and source records attributed to Ajinkya Punjal.

6 recordsLinked to original sources

arXiv2025

Broadband High-Performance Terahertz Polarizers by Nanoimprint Lithography for Advanced Applications

Terahertz polarizers are essential for advanced spectroscopic systems but face challenges like low transmission, short bandwidths and low extinction ratios. This study demonstrates the development of ultrabroadband THz polarizers using nanoimprint lithography, achieving high performance through double-wire-grid polarizer (DWGP) structures on cyclic olefin copolymer (COC) substrates. Compared to silicon-based alternatives, the polymer DWGPs demonstrated over twice the TM-polarized transmittance across the 0.1 - 25 THz range. The degree of polarization exceeded 98% in a 0.1-16 THz range, with a maximum extinction ratio above 65.4 dB at 4.2 THz. Simultaneous characterization of materials using THz time-domain spectroscopy (THz-TDS) and Fourier-transform infrared spectroscopy (FTIR) covered extended frequency ranges of 0.1 - 40 THz and 0.9 - 20 THz, respectively. Nanofabricated polymer DWGP revealed the superior optical properties, including enhanced TM transmittance and reduced TE leakage when compared to Si DWGP. Additionally, the fabricated polymer polarizers showcased cost-effectiveness, scalability, and durability, offering a sustainable alternative to conventional Si-based polarizers. The significant developments demonstrated in this study position polymer-based DWGPs as significant components for THz imaging, sensing, and wireless communication systems, paving the way for next-generation technologies.

physics.optics↗

arXiv2024

Exploring angle-dependent Phonon Modes in Sodium Mesitylene Sulfonate (SMS) crystals using THz-time domain polarimetry (THz-TDP)

We employed sodium mesitylene sulfonate crystals to investigate angle-dependent phonon resonance and thickness-dependent splitting in THz time-domain polarimetry. This crystal possesses a C2 space group, leading to a repetition pattern after 180deg rotations. Our experimental observations revealed intriguing behaviour: We observed a non-linear response when varying the angle from 10deg to 360deg in both 0.182mm and 1.266mm thick crystals. specifically, at 90deg and 270deg, dip resonance occurred, while at 180deg and 360deg, no phonon resonance was observed. For thick crystals, we observed the splitting of phonon modes. Our findings offer valuable insights into the phononic properties of this crystal as the angle varies.

physics.optics↗

arXiv2024

Probing of magnetic dimensional crossover in CrSiTe$_{3}$ through picosecond strain pulses

Elucidating the emergence of long-range magnetic ordering from its precursor short-range magnetic ordering (SRMO) in two-dimensional van der Waals materials holds profound implications for fundamental research and technological advancements. However, directly observing the intricate stages of this magnetic dimensional crossover (MDC) remains a significant experimental challenge. While magneto-elastic coupling offers a promising avenue, detecting the minute lattice response to SRMO proves challenging. Recent investigations utilizing second harmonic generation have unveiled a two-step MDC in a van der Waals ferromagnetic insulator. However, an unambiguous detection of MDC through the time-resolved techniques remains elusive. To meet this goal, we have executed an alternative approach by employing picosecond acoustic strain pulses generated by femtosecond lasers to probe the various stages of MDC through the magneto-elastic coupling for the first time. By analyzing the shape of the strain pulse in both the time and frequency domains as a function of temperature, we clearly demonstrate the detection of the subtle influence of spin fluctuations on the lattice. Additionally, the ultrafast carrier dynamics also show signatures of MDC. Our measurements pave the way towards characterizing magnetic materials in time-resolved experiments that are crucial in designing a new generation of spin-based optoelectronic devices.

cond-mat.mtrl-sci↗

arXiv2023

Ultrafast Carrier Relaxation and Second Harmonic Generation in a Higher-Fold Weyl Fermionic System PtAl

In topological materials, shielding of bulk and surface states by crystalline symmetries has provided hitherto unknown access to electronic states in condensed matter physics. Interestingly, photo-excited carriers relax on an ultrafast timescale, demonstrating large transient mobility that could be harnessed for the development of ultrafast optoelectronic devices. In addition, these devices are much more effective than topologically trivial systems because topological states are resilient to the corresponding symmetry-invariant perturbations. By using optical pump probe measurements, we systematically describe the relaxation dynamics of a topologically nontrivial chiral single crystal, PtAl. Based on the experimental data on transient reflectivity and electronic structures, it has been found that the carrier relaxation process involves both acoustic and optical phonons with oscillation frequencies of 0.06 and 2.94 THz, respectively, in picosecond time scale. PtAl with a space group of $P$$2_{1}$3 allows only one non-zero susceptibility element i.e. $d_{14}$, in second harmonic generation (SHG) with a large value of 468(1) pm/V, which is significantly higher than that observed in standard GaAs(111) and ZnTe(110) crystals. The intensity dependence of the SHG signal in PtAl reveals a non-perturbative origin. The present study on PtAl provides deeper insight into topological states which will be useful for ultrafast optoelectronic devices.

cond-mat.mes-hall↗

arXiv2022

Vanadium doped beta-Ga2O3 single crystals: Growth, Optical and Terahertz characterization

We report the growth of electrically-resistive vanadium-doped beta-Ga2O3 single crystals via the optical floating zone technique. By carefully controlling the growth parameters V-doped crystals with very high electrical resistivity compared to the usual n-type V-doped beta-Ga2O3 (ne~10^(18)/cm^3) can be synthesized. The optical properties of such high resistive V-doped b-Ga2O3 are significantly different compared to the undoped and n-doped crystals. We study the polarization-dependent Raman spectra, polarization-dependent transmission, temperature-dependent photoluminescence in the optical wavelength range and the THz transmission properties in the 0.2 - 2.6 THz range. The V-doped insulating Ga2O3 crystals show strong birefringence with refractive index contrast Dn of 0.3+-0.02 at 1 THz, suggesting it to be an ideal material for optical applications in the THz region.

cond-mat.mtrl-sci↗

arXiv2022

Terahertz Optical Properties and Birefringence in Single Crystal Vanadium doped [100] \b{eta}-Ga2O3

We report the Terahertz optical properties of the Vanadium doped [100] \b{eta}-Ga2O3 using Terahertz Time-Domain Spectroscopy (THz-TDS). The V-doped \b{eta}-Ga2O3 crystal shows strong birefringence in the 0.2-2.4 THz range. Further, phase retardation by the V-doped \b{eta}-Ga2O3 has been measured over the whole THz range by Terahertz Time-Domain Polarimetry (THz-TDP). It is observed that the V-doped \b{eta}-Ga2O3 crystal behaves both as a quarter waveplate (QWP) at 0.38, 1.08, 1.71, 2.28 THz, and a half waveplate (HWP) at 0.74 and 1.94 THz, respectively.

cond-mat.mtrl-sci↗