High-efficiency near-infrared optical parametric amplifier for intense, narrowband THz pulses tunable in the 4 to 19 THz region

Abstract

Dynamic control of material properties using strong-field, narrowband THz sources has drawn attention because it allows selective manipulation of quantum states on demand by coherent excitation of specific low-energy modes in solids. Yet, the lack of powerful narrowband lasers with frequencies in the range of a few to a few tens of THz has restricted the exploration of hidden states in condensed matter. Here, we report the optimization of an optical parametric amplifier (OPA) and the efficient generation of a strong, narrowband THz field. The OPA has a total conversion efficiency of > 55%, which is the highest value reported to date, with an excellent energy-stability of 0.7% RMS over 3 h. We found that the injection of a high-energy signal beam to a power amplification stage in an OPA leads to high-efficiency and a super-Gaussian profile. By difference-frequency generation of two chirped OPA signal pulses in an organic nonlinear crystal, we obtained a THz pulse with an energy of 3.2 μJ, a bandwidth of 0.5 THz, and a pulse duration of 860 fs tunable between the 4 and 19 THz regions. This corresponds to an internal THz conversion efficiency of 0.4% and a THz field strength of 6.7 MV/cm. This approach demonstrates an effective way to generate narrow-bandwidth, intense THz fields.

Large effective magnetic fields from chiral phonons in rare-earth halides

“…We proved that the sharply increasing magnetization in cryogenic temperatures correlates with the diverging paramagnetic susceptibility, along with the appearance of resonant atomic displacement that is evidenced by time-dependent second-harmonic generation, ruling out the mechanism of a pure transition between the crystal electric field (CEF) levels. From the rate equation of paramagnetic relaxation, we deduced the transient effective magnetic field that quantitatively agrees with the modeled phonon dynamics and the spin-phonon coupling Hamiltonian throughout the temperature range of 10 to 150 K. The strength of the effective magnetic field is proportional to the number of phonons and can potentially reach 50 T under experimentally feasible conditions ( 46 ). Our method of coherently manipulating magnetic chiral phonons may apply to a broad range of quantum materials to unravel TRS-breaking processes that involve lattice dynamics ( 15 – 19 , 31 – 33 ).…”

“…The relatively low fluence used in our experiment ensures that the magnetization is unlikely to be caused by nonlinear effects such as phonon anharmonicity or lattice-induced phase transition ( 36 , 60 ). The linear trend suggests that the transient effective magnetic field could approach 50 T when the absorbed fluence is >10 mJ/cm 2 ( 39 , 46 ), which stays below the Lindemann melting criterion and avoids significant anharmonicity ( 61 ).…”

Parameter dependencies in multicycle THz generation with tunable high-energy pulse trains in large-aperture crystals

“…Despite dedicated efforts to improve the performance of laser-driven multicycle THz sources, they still suffer from opticalto-terahertz conversion efficiencies below one percent, making it challenging to reach mJ-level pulse energies [4][5][6][7][8][9][10][11][12][13][14][15]. In order to increase conversion efficiencies, sophisticated ideas have been developed based on tailoring the spectrum and the temporal shape of the pump laser pulses.…”

Phonon Polaritonics in Broad Terahertz Frequency Range with Quantum Paraelectric SrTiO3

“…[ 18 ] Despite the tremendous progress, a free‐space electric field up to GV m −1 in this frequency range can only be achieved with table‐top sources under extreme conditions. [ 19–21 ] Many photonic structures can locally enhance field, [ 22–24 ] but there are few materials with low loss and high damage threshold for constructing devices in 5–15 THz.…”