Few-cycle pulses tunable from 3 to 7  µm via intrapulse difference-frequency generation in oxide LGN crystals

Abstract

An ultrashort mid-infrared (IR) source beyond 5 µm is crucial for a plethora of existing and emerging applications in spectroscopy, medical diagnostics, and high-field physics. Nonlinear generation of such sources from well-developed near-IR lasers, however, remains a challenge due to the limitation of mid-IR crystals. Based on oxide L a 3 G a 5.5 N b 0.5 O 14 (LGN) crystals, here we report the generation of femtosecond pulses tunable from 3 to 7 µm by intrapulse difference-frequency generation of 7.5 fs, 800 nm pulses. The efficiency and bandwidth dependences on pump polarization and crystal length are studied for both Type-I and Type-II phase-matching configurations. Maximum pulse energy of ∼ 10 n J is generated at 5.2 µm with a conversion efficiency of ∼ 0.14 % . Because of the few-cycle pump pulse duration, the generated mid-IR pulses are as short as about three cycles. These results, to the best of our knowledge, represent the first experimental demonstration of LGN in generating mid-IR ultrashort pulses.

Maximizing the efficiency of intrapulse difference frequency generation by pulse shaping and recycling

“…On the other hand, iDFG is very attractive with a straightforward implementation, inherent spatial-temporal overlap. Nevertheless, the conversion efficiencies associated with this technique generally tend to be lower than those of OPA-based sources (<0.5%, typically around 0.1% at wavelengths ranging from 6 to 10 µm) [3,[19][20][21][22]. This arises from the fact that only a fraction of the pump photons contributes to the interaction, both in terms of spectral content and polarization state.…”

Birefringence Dispersion Management of Langasite Nonlinear Crystals for the Improvement of Mid-Infrared Amplification

“…To date, the optical parametric chirped-pulse amplification (OPCPA) is one of the few highly effective ways to realize the mid-IR ultrashort and ultra-intense lasers, wherein the suitable mid-IR nonlinear optical (NLO) crystal with high damage thresholds and transmission spectral ranges is critical but few, besides the favorable effective nonlinear coefficients. , Recently, langasite crystals were identified as the candidate for the mid-IR OPCPA because of their reduced second-order phonon absorption by 2-fold rotation symmetry of (DO 4 ) tetrahedron, and among them, the La 3 Nb 0.5 Ga 5.5 O 14 (LGN) crystal was proposed to be the favorable nonlinear material , that possesses a wider transmission range (0.28–7.4 μm) than traditional oxide NLO crystals (such as the commonly applied LiNbO 3 and KTiOAsO 4 ) , due to the relatively low phonon frequency and high laser damage threshold (LDT) (1.41 GW@1.064 μm@10 ns) resulting from its large bandgap. , Meanwhile, the LGN crystal is also feasible to be directly pumped by the commercial and well-developed near-infrared lasers to achieve the mid-IR laser output . An OPCPA system based on the LGN crystal with favorable characteristics of 5.2 μm, 130 GW, and 120 fs pulses has been theoretically designed, and a tunable seed pulse ranging from 3 to 7 μm has been achieved . However, despite the ability to grow a large bulk, the practical application of the LGN crystal still suffers from the relatively small effective NLO coefficient d eff due to the birefringence dispersion determined phase-matching conditions, which is crucial in determining the overall OPCPA performance due to the basic laser intensity dependences I ∝ d eff 2 …”

“…6 An OPCPA system based on the LGN crystal with favorable characteristics of 5.2 μm, 130 GW, and 120 fs pulses has been theoretically designed, 7 and a tunable seed pulse ranging from 3 to 7 μm has been achieved. 12 However, despite the ability to grow a large bulk, the practical application of the LGN crystal still suffers from the relatively small effective NLO coefficient d eff 12 due to the birefringence dispersion determined phase-matching conditions, which is crucial in determining the overall OPCPA performance due to the basic laser intensity dependences I ∝ d eff 2 . 13 Associated with the nonlinear optical theory, the d eff is determined by the quadratic independent second-order susceptibility d ijk and phase-matching (PM) conditions (θ, φ) dependent on the birefringence dispersion.…”

Pump-induced thermo-optic manifestation lead adiabatic ultrashort-pulse optical parametric generation in long LiNbO3 crystals

“…The presence of an optical cavity brings in significant design as well as operational complexity which entails optimum beam alignment, pulse synchronization, cavity-stabilization, and thermal-load management [9,10]. In order to execute single-pass broadband parametric down conversion, techniques based on group-velocity-matching (GVM) [11][12][13], chirped quasi-phase-matched (QPM) gratings [14,15], and non-collinear dispersion compensating schemes have been employed [16,17]. All such techniques exhibit a trade-off between signal-idler frequency tunability and conversion efficiency.…”