Edilson L. Falcão-Filho

Highly stable ultrabroadband mid-IR optical parametric chirped-pulse amplifier optimized for superfluorescence suppression.

We present a 9 GW peak power, three-cycle, 2.2 microm optical parametric chirped-pulse amplification source with 1.5% rms energy and 150 mrad carrier envelope phase fluctuations. These characteristics, in addition to excellent beam, wavefront, and pulse quality, make the source suitable for long-wavelength-driven high-harmonic generation. High stability is achieved by careful optimization of superfluorescence suppression, enabling energy scaling.

Analytic scaling analysis of high harmonic generation conversion efficiency

Closed form expressions for the high harmonic generation (HHG) conversion efficiency are obtained for the plateau and cutoff regions. The presented formulas eliminate most of the computational complexity related to HHG simulations, and enable a detailed scaling analysis of HHG efficiency as a function of drive laser parameters and material properties. Moreover, in the total absence of any fitting procedure, the results show excellent agreement with experimental data reported in the literature. Thus, this paper opens new pathways for the global optimization problem of extreme ultraviolet (EUV) sources based on HHG.

Nonintrusive phase stabilization of sub-two-cycle pulses from a prismless octave-spanning Ti:sapphire laser.

Carrier-envelope (CE) phase-stabilized sub-two-cycle pulses are generated from a 500 MHz compact prismless octave-spanning laser without extracavity nonlinear optical processes distorting the laser output. The necessary f and 2f spectral components are generated intracavity and coupled out independently from the main pulse through specially designed cavity mirrors, resulting in a 55 dB CE beat note (100 kHz resolution bandwidth). The in-loop CE phase error (integrated from 2.5 mHz to 10 MHz) is 67 mrad, equivalent to a timing jitter between carrier and envelope of 28 as at 790 nm.

Antimony orthophosphate glasses with large nonlinear refractive indices, low two-photon absorption coefficients, and ultrafast response

Antimony glasses based on the composition Sb2O3–SbPO4 were prepared and characterized. The samples present high refractive index, good transmission from 380to2000nm, and high thermal stability. The nonlinear refractive index, n2, of the samples was studied using the optical Kerr shutter technique at 800nm. The third-order correlation signals between pump and probe pulses indicate ultrafast response (<100fs) for all compositions. Enhancement of n2 was observed by adding lead oxide to the Sb2O3–SbPO4 composition. Large values of n2≈10−14cm2∕W and negligible two-photon absorption coefficients (smaller than 0.01cm∕GW) were determined for all samples. The glass compositions studied present appropriate figure-of-merit for all-optical switching applications.

High-order nonlinearity of silica-gold nanoshells in chloroform at 1560 nm.

The nonlinear response of silica--gold nanoshells (SGNs) in chloroform was studied using laser pulses of 65 fs at 1560 nm. The experiments were performed using the thermally managed Z--scan technique that allows measurements of the electronic contribution for the nonlinear response, free from thermal influence. The results were analyzed using an analytical approach based on the quasi--static approximation that allowed extraction of the nonlinear susceptibility of a SGN from the data. High third--order susceptibility, χsh((3)) = - 1.5 x 10(-11) m(2)/V(2), approximately four orders of magnitude larger than for gold nanospheres in the visible, and large fifth--order susceptibility, χsh((5)) = - 1.4 x 10(-24) m(4)/V(4), were obtained. The present results offers new perspectives for nonlinear plasmonics in the near--infrared.

Frequency upconversion involving triads and quartets of ions in a Pr3+/Nd3+ codoped fluoroindate glass

Frequency upconversion (UC) processes involving energy transfer (ET) among Nd3+ and Pr3+ ions in a fluoroindate glass are reported. In a first experiment, the excitation of Pr3+ [transition 3H4→1D2] and of Nd3+ [transition 4I9/2→(2G7/2+4G5/2)] was achieved with a dye laser operating in the 575–590 nm range. In a second experiment, the Nd3+ ions were excited with the second harmonic of a Nd: YAG laser at 532 nm. The ET processes leading to UC in both experiments were studied by monitoring the blue fluorescence decay at 480 nm due to the transition 3P0→3H4 in Pr3+. In the more relevant UC process, quartets of ions (Nd–Nd–Pr–Pr) are excited due to absorption of three laser photons by two Nd3+ ions which transfer their energy to two Pr3+ ions. Each Pr3+ ion promoted to the 3P0 level decays to the ground state emitting one photon in the blue region. This conclusion was achieved investigating the dependence of the UC fluorescence intensity as a function of laser intensity, samples concentrations, and temporal b...

Optical limiting behavior of bismuth oxide-based glass in the visible range

The authors report experimental results on the optical limiting behavior of a bismuth oxide-based glass by exciting the samples with nanosecond laser pulses at 532 and 598 nm. The results show that two-photon and free-carrier absorption processes contribute for the nonlinear absorption. Values for beta, the two-photon absorption coefficient, and sigma_e, the absorption cross section due to free carriers, were determined. The values for beta and sigma_e are dependent on the amount of bismuth oxide in the glass composition.

Scaling of high-order harmonic efficiencies with visible wavelength drivers: A route to efficient extreme ultraviolet sources

Scaling of high-order harmonic generation (HHG) efficiency versus drive wavelength is experimentally studied using 800 and 400 nm pulses and theoretically modeled for visible drive wavelength. We demonstrate good agreement of experimental results with the calculations from a recently established semianalytic HHG model and discuss the feasibility of efficient-HHG-based extreme ultraviolet sources driven by visible ultrafast lasers. Our study shows that efficiencies of >10−5 can be achieved at ∼90 eV by selecting appropriate drive wavelengths with He under good phase matching conditions.

Picosecond third-order nonlinearity of lead-oxide glasses in the infrared

Heavy metal-oxide glasses containing lead and bismuth were prepared, and their picosecond third-order nonlinear (NL) optical characteristics were investigated. NL refractive indices of ≈10−18m2∕W at 1064nm were measured. Negligible NL absorption was verified and, as a consequence, the samples present a good factor-of-merit for photonic applications.

Nonlinear optical properties of tungstate fluorophosphate glasses

The optical nonlinearity of tungstate fluorophosphate glasses, synthesized in the NaPO3-BaF2-WO3 system, was investigated through experiments based on the third-order susceptibility, χ(3). Nonlinear (NL) refraction and NL absorption measurements in the picosecond regime were performed using the Z-scan technique at 532 nm. NL refractive index, n2∝Re χ(3), ranging from 0.4×10−14 cm2/W to 0.6×10−14 cm2/W were determined. The two-photon absorption coefficient, α2∝Im χ(3), for excitation at 532 nm, vary from 0.3 to 0.5 cm/GW. Light induced birefringence experiments performed in the femtosecond regime indicate that the response time of the nonlinearity at 800 nm is faster than 100 fs. The experiments show that χ(3) is enhanced when the WO3 concentration increases and this behavior is attributed to the hyperpolarizabilities associated to W–O bonds.