Pola larized Terahertz (THz) Radia iation Lab symbolics - PowerPoint PPT Presentation

Im Impact of Hot-Ele lectron on Efficient Radia ially Pola larized Terahertz (THz) Radia iation Lab symbolics Manendra*, Ruchi Bhati and Anil K Malik or author photo Department of Physics, Ch. Charan Singh University Meerut, UP-250004, India Email id: manendrac@gmail.com Abstract Theory Theoretical Model Results Results Conclusion Due to diverse applications in material characterization, imaging, topography, remote sensing, chemical, outer space communication, submillimetre radars and security identification [1-6], have attracted the trust of many researchers. We propose a theoretical model for radially polarized THz radiation generation by frequency mixing of radially polarized CW CO 2 Top-Hat lasers in corrugated plasma. In our theoretical model, we investigate the effect of electron temperature, laser beam quality and profile on emitted THz radiation. Radially polarized THz field amplitude is maximum around the resonance excitation ( 𝝏 𝟐 − 𝝏 𝟑 = 𝝏 𝒓 ≈ 𝝏 𝒒 ) and decreases drastically with mismatch of 𝝏 𝒓 and 𝝏 𝒒 . In our numerical study under the optimized parameters, radially polarized THz radiation with high electric field and the efficiency can be obtained to meet the demands of THz radiation-matter interactions, nonlinear THz spectroscopy and imaging, etc. Radially polarized THz field is more convenient to penetrate deeply without risk of collateral damage of inside the skin layers thereby improved safety and efficacy of treatment [7]. References [1] Dragoman D and Dragoman M 2004 Prog. Quantum Electron. 28 10 [2] Siegel P H 2002 IEEE Trans. Microw. Theory Tech. 50 910 [3] Leemans W P et al 2003 Phys. Rev. Lett. 91 074802 [4] Ebbinghaus S, Schröck K, Schauer J C, Bründermann E,Heyden M, Schwaab G, Böke M, Winter J, Tani M and Havenith M 2006 Plasma Sources Sci. Technol. 15 72. [5] Schroeder C B, Esarey E, Tilborg J Van and Leemans W P 2004 Phys. Rev. E 69 016501 [6] Sizov F 2010 Opto Electron. Rev. 18 10. [7] B. Varghese, S. Turco, V. Bonito, and R. Verhagen, 2013 Opt. Express 21, 18304.

Im Impact of of Hot-Electron on on Efficient Ra Radiall lly Pol olarized Terahertz (TH (THz) Ra Radiation Lab symbolics Manendra*, Ruchi Bhati and Anil K Malik Abstract Theory Theoretical Model Results Results Conclusion Introduction THz radiation are electromagnetic waves situated between the infrared and microwave regions of the spectrum. The THz frequency range is defined as the region of the electromagnetic spectrum in the range of 100 GHz (3 mm) to 10 THz (30 μm ), which is between the millimeter and infrared frequencies. The THz band FIG: Schematic has been called by several names, such as sub-millimeter, far infrared, and near- diagram showing the millimeters wave. The active investigations of the terahertz spectral region. location of THz band Terahertz (THz) radiation is generally defined as the These properties can be in the electromagnetic summarized as follows: spectrum 1.Penetration: The wavelength of THz radiation is longer than the infrared wavelength; hence, THz waves have less scattering and better penetration depths (in the range of cm) compared to infrared ones (in the range of μm ). Therefore, dry and non-metallic materials are transparent in this range but are opaque in the At 1 THz, the radiated signal has the following characteristics: visible spectrum. • Wavelength: 300 μm in free space 2.Resolution: THz waves have shorter wavelengths in comparison to the • Period: 1 ps, microwave ones; this gives a better spatial imaging resolution. • Photon energy: 4.14 meV 3.Safety: The photon energies in the THz band are much lower than X-rays. Therefore, THz radiation is non-ionizing. References 4.Spectral fingerprint: Inter- and intra-vibrational modes of many molecules lie in [8] TONOUCHI M 2007 Nat. Photonics 1, 97. THz range [9] Ferguson B and Zhang X 2002 Nat. Mater. 1, 26.

Im Impact of of Hot-Electron on on Efficient Ra Radiall lly Pol olarized Terahertz (TH (THz) Ra Radiation Lab symbolics Manendra*, Ruchi Bhati and Anil K Malik Abstract Theory Theoretical Model Results Results Conclusion C 𝐗 𝑫𝑷 𝟑 Laser profile Schematic of THz radiation generation ➢ Laser Profile 𝑡 1 − 𝑠 𝑠 𝑓 𝑗 𝑙 𝑘 𝑨−𝜕 𝑘 𝑢 𝑘 𝑠, 𝑨 = ൞ Ƹ 𝑠𝐹 0 𝑥ℎ𝑓𝑠𝑓 < 1, 𝐹 a 0 a 0 j=1,2 0 𝑝𝑢ℎ𝑓𝑠𝑥𝑗𝑡𝑓 FIG.: Laser electric field distribution of pump lasers along x and y directions. The laser beam width 𝑏 0 = 50𝜈𝑛 when the laser field profile index (a) s =1, (b) s = 2, (c) s = 3, (d) s = 4. FIG.: Schematic of THz radiation generation by Triangular (top hat like) lasers in the ripple density hot Plasma. References [ 10] Manendra et al. Phys. Plasmas 27, 023108 (2020)

Ƹ Im Impact of of Hot-Electron on on Efficient Ra Radiall lly Pol olarized Terahertz (TH (THz) Ra Radiation Lab symbolics Manendra*, Ruchi Bhati and Anil K Malik Abstract Theory Theoretical Model Results Results Conclusion Phase matching Condition and Resonance Terahertz (THz Radiation) Generation ➢ Pondermotive Force pon (𝑠, 𝑨) = 𝑓 2 𝐹 0 𝑡 𝑡−1 𝑡 2 1 − 𝑠 2𝑡 𝑠 𝑠 − 𝑗𝑙 ′ 1 − 𝑠 ẑ 𝑓 𝑗 𝑙 ′ 𝑨−𝜕 ′ 𝑢 Ԧ 𝑔 2𝑛 𝜕 1 𝜕 2 a 0 a 0 a 0 a 0 ➢ Normalized Terahertz Field 2 2 vth vth 𝑡 ω 2 1− 2 𝜕 𝑞 2 𝑤 2 ∗ − c2 𝜕 𝑞 𝑡−1 𝑡 c2 𝑜 𝜈 𝐹 THz 𝑠 𝑠 ∗ = 𝑓𝐹 02 = 1 − where v 2 2 𝐹 0 𝑜 0 2 a 0 a 0 𝑛𝑗𝜕 2 v th 2𝜕 1 a 0 ω 2 1− 2 −𝜕 𝑞 c2 ➢ Phase Matching Condition 1/2 2 𝑑𝑙 𝜈 𝜕 𝑞 𝜕 𝜕 𝑞 = 1 − − 1 . 2 𝜕 𝑞 vth 𝜕 2 1− c2 References [10] Manendra et al. Phys. Plasmas 27, 023108 (2020)

Im Impact of of Hot-Electron on on Efficient Ra Radiall lly Pol olarized Terahertz (TH (THz) Ra Radiation Lab symbolics Manendra*, Ruchi Bhati and Anil K Malik Abstract Theory Theoretical Model Results Results Conclusion THz Field distribution THz conversion efficiency ➢ Efficiency of scheme is calculated using energy densities of pumped lasers and THz radiation. 2 2 2 ∗ 2 ω 2 1 − v th − v th 4 𝑤 2 2 𝜕 𝑞 2 𝑜 𝜈 c 2 𝜕 𝑞 c 2 𝑡 2 (𝑡 + 1)(2𝑡 + 1 ) 𝜃 = 2 4𝑡 − 1)(3𝑡 − 1)(2𝑡 − 1 2 2 ω 2 1 − v th 2 𝜕 1 2 a 0 2 8𝑜 0 − 𝜕 𝑞 c 2 References [10] Manendra et al. Phys. Plasmas 27, 023108 (2020)

Im Impact of Hot-Ele lectron on Efficient Radia ially Pola larized Terahertz (THz) Radia iation Lab symbolics Manendra*, Ruchi Bhati and Anil K Malik or author photo Department of Physics, Ch. Charan Singh University Meerut, UP-250004, India Email id: manendrac@gmail.com Abstract Theory Theoretical Model Results Results Conclusion In this theoretical model predicts that nonlinear mixing of bicolor radially polarized lasers with top-hat (s >1) laser field envelopes in density modulated hot plasma excites very high intensity (normalized electric field ≈ GV/m) radially polarized THz waves in the forward direction. ➢ THz field profile and amplitude strongly depend on the laser envelope parameters, which can be tuned with the help of laser profile parameter s. ➢ THz field in the case of resonant frequencies is much higher than that in the case of off-resonant frequencies. ➢ THz amplitude increases with electron temperature without affecting the resonance condition. ➢ The location of the THz field peak and field distribution depends only on the laser profile parameter and are independent of the electron temperature. ➢ Artificial density modulation in plasma helps in achieving phase matching. For high electron temperature, small λ 𝜈 is needed to obtain phase matching. ➢ THz conversion efficiency increases fivefold with an increase in electron thermal velocity from v 𝑢ℎ = 0 to v 𝑢ℎ = 0 .2c. ➢ THz conversion efficiency of 10% is predicted for optimized laser and plasma parameters.