Using a self-assembly of recombinant spidroins, biomimetic spinning dopes are produced and wet-spun into fibers. Upon varying the molecular design of the underlying recombinant spidroins, the influence of the amino- and carboxy-terminal domains, as well as the size of the repetitive core domain on fiber mechanics, is determined. Fiber toughness upon biomimetic processing equals and even slightly exceeds that of natural ones.

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Single‐walled carbon‐nanotube absorbers are experimentally demonstrated for laser mode‐locking. A saturable absorber device is used to mode‐lock three different bulk solid‐state lasers in a 500 nm‐wide wavelength interval. The devices exhibit a low saturation fluence of <10 µJ cm−2, low scattering losses, and an exceptionally rapid relaxation, with time constants reaching <100 fs. The latter two properties are explained by a decreased curling tendency and increased tube‐to‐tube interactions of the nanotubes, respectively. These properties are the result of an optimized manufacturing procedure in combination with the use of a starting material with a higher microscopic order. The decreased scattering enables universal use of these devices in bulk solid‐state lasers, which tend to be highly sensitive against non‐saturable device losses as caused by scattering. The favorable saturable absorption properties are experimentally verified by mode‐locking the three lasers, which all exhibit near transform‐limited performance with about 100 fs pulse duration. The complete and unconditional absence of Q‐switching side bands verifies the small saturation fluence of these devices.

Mode locking of an Yb-doped bulk laser in the 1 microm spectral range using a single-walled carbon nanotube saturable absorber (SWCNT-SA) is demonstrated for the first time, to our knowledge. Passive mode locking of an Yb:KLuW laser resulted in nearly transform-limited pulses as short as 115 fs at 1048 nm. In addition, the nonlinear response of the SWCNT-SA was measured, yielding a modulation depth of 0.25% and a relaxation time of 750 fs.

Stable and self-starting mode-locking of a Tm:KLu(WO(4))(2) crystal laser is demonstrated using a transmission-type single-walled carbon nanotube (SWCNT) based saturable absorber (SA). These experiments in the 2 microm regime utilize the E11 transition of the SWCNTs for nonlinear saturable absorption. The recovery time of the SWCNT-SA is measured by pump-probe measurements as approximately 1.2 ps. The mode-locked laser delivers approximately 10 ps pulses near 1.95 microm with a maximum output power of up to 240 mW at 126 MHz repetition rate.

Electrooptical (EO) materials are able to change their refractive index under the influence of an externally applied electric field, an effect that is of great technological importance as a means to control the phase of laser light. [1] In recent years, a variety of cheap and easily processable organic nonlinear optical (NLO) materials [2] were designed for this purpose. Poled polymers for high-frequency modulation of optical signals were developed, and photorefractive (PR) polymers [3] emerged as promising materials for widespread holographic optical applications. In both types of material, the EO response is provided by chromophores that are usually incorporated into the material as guests or as side-groups in functionalized polymers. In this communication, we analyze the microscopic mechanism leading to the refractive index modulation and define appropriate molecular figures-of-merit (FOMs) for EO chromophores, F 0 Pockels and F 0 Kerr . In order to investigate optimization strategies for both FOMs, we synthesized a series of dyes based on quinonoid carbocyclic and heterocyclic acceptor units, which exhibit significantly higher acceptor strength and better thermal stability than common open-chain acceptor groups.All chromophores investigated in this study are displayed in Figure 1. The synthetic procedures for the new EO dyes 4±11 are shown in Schemes 1 and 2. Accordingly, EO dyes 4 and 10 were prepared by Knoevenagel condensations of p-N,N-dimethylamino cinnamaldehyde (13a) with benzylidene malononitrile 15 [4] and 1-naphthylmalononitrile (16) [5] in acetic acid anhydride in yields of 72 and 43 %, respectively (Scheme 1). Similarly, dye 3 (DCM, a commercial laser dye) was obtained according to the literature from 14. [6] For dye 11, the polyenic chain of 13b was extended via a Wittig oxopropenylation [7] using the protected formylmethylenetriphenylphosphorane 17 to give pentadienal 18 in 60 % yield. The following condensation of 18 with 16 gave 11 in 10 % yield. The EO dyes 5±9, bearing the new powerful thiazolidenemalononitrile acceptor unit, were synthesized according to Scheme 2. Reaction of stoichiometric amounts of a-thiocyanatoketones 19a and b with malononitrile afforded 2-dicyanomethylthiazoles 20a and b in almost quantitative yields. [8] Because of an equilibrium between various tautomeric forms, these heterocycles may react easily in condensation reactions with aldehydes 13a and b, 21, and 22 to give dyes 5, 6, and 9a and b in yields of 60±80 %. The corresponding aldehydes 21 and 22 were obtained from N,N-dibutylaniline and N-alkylated 3,3-dimethyl-2-methyleneindoline by Vilsmeier formylations. For the synthesis of EO dyes 7 and 8 the reaction conditions had to be changed because of the high basicity of the methylene bases of 23 and 24. In a one-pot sequence in acetic acid anhydride, 3ethyl-2-methylbenzoxazolium iodide (23) and 1-hexyl-4methylpyridinium bromide (24) were first converted to the anils by N,N-diphenylformamidine (DPFA). They were then in-situ N-acetylated at 150 C, [9] before being ...

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Direct sub-50-fs pulse generation is demonstrated with a mode-locked Yb:YCa4O(BO3)3 laser. With external compression, pulses as short as 35 fs are generated at 1055 nm. The oscillator operating at a repetition rate of 95 MHz is pumped by a two-section distributed Bragg reflector tapered diode laser and mode locked by a semiconductor saturable absorber mirror. The onset of self-Raman-conversion for pulse spectral bandwidths exceeding 40 nm (FWHM) is observed.