Conjugated polymer-fullerene blend with strong optical limiting in the near-infrared

Temporal contrast reduction techniques for high dynamic-range temporal contrast measurement

A single-shot characterization of the temporal contrast of a petawatt laser pulse with a high dynamic-range, is important not only for improving conditions of the petawatt laser facility itself, but also for various high-intensity laser physics experiments, which is still a difficult problem. In this study, a new idea for improving the dynamic-range of a single-shot temporal contrast measurement using novel temporal contrast reduction techniques is proposed. The proof-of-principle experiments applying single stage of pulse stretching, anti-saturated absorption, or optical Kerr effect successfully reduce the temporal contrast by approximately one order of magnitude. Combining with the SRSI-ETE method, its dynamic-range characterization capability is improved by approximately one order of magnitude to approximately 10⁹. It is expected that a higher dynamic-range temporal contrast can be characterized by using cascaded temporal contrast reduction processes. The proposed techniques can also be used in the delay-scanning temporal contrast measurement to improve its dynamic range.

Polyfluorenylacetylene for near-infrared laser protection: polymer synthesis, optical limiting mechanism and relationship between molecular structure and properties

The incorporation of styryl/stilbene–fluorene into polyacetylenes not only endowed the polymers with novel near-infrared optical limiting properties based on a two-photon absorption mechanism but good solubility and high thermal stability.

Broadband Two-Photon Absorption Characteristics of Highly Photostable Fluorenyl-Dicyanoethylenylated [60]Fullerene Dyads

We synthesized four C₆₀-(light-harvesting antenna) dyads C₆₀ (>CPAF-C_n) (n = 4, 9, 12, or 18) 1-C_n for the investigation of their broadband nonlinear absorption effect. Since we have previously demonstrated their high function as two-photon absorption (2PA) materials at 1000 nm, a different 2PA wavelength of 780 nm was applied in the study. The combined data taken at two different wavelength ranges substantiated the broadband characteristics of 1-C_n. We proposed that the observed broadband absorptions may be attributed by a partial π-conjugation between the C₆₀ > cage and CPAF-C_n moieties, via endinitrile tautomeric resonance, giving a resonance state with enhanced molecular conjugation. This transient state could increase its 2PA and excited-state absorption at 800 nm. In addition, a trend of concentration-dependent 2PA cross-section (σ₂ ) and excited-state absorption magnitude was detected showing a higher σ value at a lower concentration that was correlated to increasing molecular separation with less aggregation for dyads C₆₀(>CPAF-C₁₈) and C₆₀(>CPAF-C₉), as better 2PA and excited-state absorbers.

Near-IR nonlinear optical filter for optical communication window

We report on a high performance nonlinear optical filter for the telecommunication window that employs detonation nanodiamonds (NDs). The nanosecond Z-scan experiments revealed that the heavy water ND suspensions enable strong optical limiting in the wavelength range of 1400-1675 nm. We observed an enhancement of the optical limiting performance in the blue part of the communication window. In particular, at the wavelength of 1400 nm the transmittance of the 2 mm thick sample with 4.5 wt. % ND concentration is suppressed by 45% for the input fluence of 3.8  J/cm(2). The proposed nonlinear optical filter employs the phenomena of the nonlinear absorption and the nonlinear light scattering in ND suspensions.

Large reverse saturable absorption under weak continuous incoherent light

In materials showing reverse saturable absorption (RSA), the optical absorbance increases as the power of the light incident on them increases. To date, RSA has only been observed when very intense light sources, such as short-pulse lasers, are used. Here, we show that hydroxyl steroidal matrices embedding properly designed aromatic molecules as acceptors and transition-metal complexes as donors exhibit high RSA on exposure to weak incoherent light at room temperature and in air. Accumulation by photosensitization of long-lived room-temperature triplet excitons in acceptors with a large triplet-triplet absorption coefficient allows a nonlinear increase in absorbance also under low-power irradiation conditions. As a consequence, continuous exposure to weak light significantly decreases the transmittance of thin films fabricated with these compounds. These optical limiting properties may be used to protect eyes and light sensors from exposure to intense radiation generated by incoherent sources and for other light-absorption applications that have not been realized with conventional RSA materials.