3D Numerical Simulations of THz Generation by Two-Color Laser Filaments

Abstract

Terahertz (THz) radiation produced by the filamentation of two-color pulses over long distances in argon is numerically investigated using a comprehensive model in full space-time-resolved geometry. We show that the dominant physical mechanism for THz generation in the filamentation regime at clamping intensity is based on quasi-dc plasma currents. The calculated THz spectra for different pump pulse energies and pulse durations are in agreement with previously reported experimental observations. For the same pulse parameters, near-infrared pump pulses at 2 μm are shown to generate a more than 1 order of magnitude greater THz yield than pumps centered at 800 nm.

Boosting Terahertz Generation in Laser-Field Ionized Gases Using a Sawtooth Wave Shape

“…This departs from the order of magnitude increase reported from setups with different focusing conditions in Refs. [16,23], but remains consistent with the nonmonotonic…”

“…In such two-color pump setup, free electrons produced by tunnel ionization acquire a nonzero drift velocity and generate a quasi-dc current which is responsible for THz emission [19]. The mechanism underlying THz generation in gases is intrinsically related to the optically induced stepwise increase of the free electron density near the extrema of the ionizing optical field [15,16,22]. An easy explanation is that the Fourier transform of a steplike function in time has its maximum near the zero frequency.…”

“…This gas-based scheme for THz generation provides higher breakdown threshold and broader spectral ranges than the method involving crystals [11][12][13][17][18][19][20]. THz pulses in gases with high field strength > 1 GV=m were simulated in [16]; however, the highest reported THz energies (5 μJ) correspond to conversion efficiencies of about 10 −4 only.In this Letter, we exploit degrees of freedom given by appropriately chosen pump waveforms beyond a simple two-color field to increase the THz conversion efficiency. We show that fields with a sawtoothlike temporal shape do promote the highest THz signals triggered by tunnelinduced photocurrents.…”

“…Recently, large-sized organic crystals were used to deliver THz pulses with GV=m electric field strength, and a conversion efficiency of about 1% was demonstrated [10]. The second method is based on focusing a femtosecond pulse together with its second harmonic into a gas cell and create a plasma [11][12][13][14][15][16][17][18][19][20][21][22][23][24]. In such two-color pump setup, free electrons produced by tunnel ionization acquire a nonzero drift velocity and generate a quasi-dc current which is responsible for THz emission [19].…”

Regularizing Aperiodic Cycles of Resonant Radiation in Filament Light Bullets

“…It is used for the investigation of, e.g., supercontinuum [5], high harmonic [6], or terahertz generation [7], few-cycle pulse generation [8], or complex nonlinear dynamics as self-organization [9]. Analogies to other areas of physics as artificial event horizons [10] or the ubiquitous rogue wave formation [11][12][13] have been shown, providing a useful test for the investigation Hawking radiation [14] or the predictability of extreme events [15].…”