Abstract
In the present work, an opportunity of nearly single-cycle THz pulse generation in aperiodically poled lithium niobate (APPLN) crystal is studied. A radiating antenna model is used to simulate the THz generation from chirped APPLN crystal pumped by a sequence of femtosecond laser pulses with chirped delays (m = 1, 2, 3 …) between adjacent pulses. It is shown that by appropriately choosing Δtm, it is possible to obtain temporal overlap of all THz pulses generated from positive (or negative) domains. This results in the formation of a nearly single-cycle THz pulse if the chirp rate of domain length δ in the crystal is sufficiently large. In the opposite case, a few cycle THz pulses are generated with the number of the cycles depending on δ. The closed-form expression for the THz pulse form is obtained. The peak THz electric field strength of 0.3 MV/cm is predicted for APPLN crystal pumped by a sequence of laser pulses with peak intensities of the separate pulse in the sequence of about 20 GW/cm2. By focusing the THz beam and increasing the pump power, the field strength can reach values in the order of few MV/cm.
Highlights
The number of applications that require intense terahertz (THz) pulses has been rapidly increasing in recent years [1,2]
To escape 2nd- and 3rd-order multiphoton pump absorption (MPA), these materials have to be pumped at longer wavelengths λp ≥ 1.7 μm, where it is still relatively challenging to obtain femtosecond laser pulses with the required high power
A simple theoretical model is developed for nearly single-cycle THz pulse generation in a chirped
Summary
The number of applications that require intense terahertz (THz) pulses has been rapidly increasing in recent years [1,2]. The operation principle is similar to that presented in [20]; it is physically based on the fact that the temporary overlap of a sufficiently large number of phase-locked spectral components leads to the formation of an ultrashort pulse It is well-known [16,17,18] that in the case of APPLN crystal pumping by single transform-limited laser pulse the generated THz waveform corresponds to domain structure of the crystal. It corresponds to spatial reversal replica (or so-called phase-conjugate replica) of the APPLN domain lengths distribution, considering that the exciting laser pulse propagates faster than the radiated THz-wave. By focusing the THz beam and using higher pump power, the electric field strength can be increased by an order of magnitude
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