Femtosecond laser waveguide micromachining of PMMA films with azoaromatic chromophores

Fabrication of magneto-optical waveguides inside transparent silica xerogels containing ferrimagnetic Fe3O4 nanoparticles

Magneto-optical waveguides with a refractive-index change were successfully fabricated inside silica xerogels containing ferrimagnetic Fe₃O₄ nanoparticles (NPs) using femtosecond laser processing. Aminopropyltriethoxysilane-derived xerogels were prepared via a sol-gel process with aqueous solutions of Fe₃O₄ NPs synthesized by coprecipitation. The mass/volume concentration of Fe₃O₄ NPs in the xerogels was determined by comparing the absorbance of the xerogel with that of an aqueous solution of Fe₃O₄ NPs. We evaluated Faraday rotation angles for light propagating through waveguide structures in xerogels containing Fe₃O₄ NPs at mass/volume concentrations of 0.087 and 0.148 mg/cm³ at a wavelength of 488 nm. Ferrimagnetic saturation of the Faraday rotation angle was observed, which is consistent with the magnetization curves measured at room temperature. Magneto-optical waveguides can potentially be used to produce micro-sized Faraday devices, such as optical isolators, high-density magnetic recording devices, and optical sensors, which can be integrated with optical and electronic hybrid circuits.

Femtosecond laser high-efficiency drilling of high-aspect-ratio microholes based on free-electron-density adjustments

We studied the micromachining of high-aspect-ratio holes in poly(methylmethacrylate) using a visible double-pulse femtosecond laser based on free-electron-density adjustments. Hole depth and aspect ratio increased simultaneously upon decreasing the wavelength in the visible-light zone. When the pulse energy reached a high level, the free-electron density was adjusted by using a double-pulse laser, which induced fewer free electrons, a lower reflectivity plasma plume, and more pulse energy deposition in the solid bottom. Thus, the aspect ratio of the hole was improved considerably. At a moderate pulse energy level, a 1.3-1.4 times enhancement of both the ablation depth and the aspect ratio was observed when the double-pulse delay was set between 100 and 300 fs, probably due to an enhanced photon-electron coupling effect through adjusting the free-electron density. At a lower pulse energy level, this effect also induced the generation of a submicrometer string. In addition, the ablation rate was improved significantly by using visible double pulses.

Molecular structure-optical property relationships for a series of non-centrosymmetric two-photon absorbing push-pull triarylamine molecules

This article reports on a comprehensive study of the two-photon absorption (2PA) properties of six novel push-pull octupolar triarylamine compounds as a function of the nature of the electron-withdrawing groups. These compounds present an octupolar structure consisting of a triarylamine core bearing two 3,3′-bis(trifluoromethyl)phenyl arms and a third group with varying electron-withdrawing strength (H < CN < CHO < NO2 < Cyet < Vin). The 2PA cross-sections, measured by using the femtosecond open-aperture Z-scan technique, showed significant enhancement from 45 up to 125 GM for the lowest energy band and from 95 up to 270 GM for the highest energy band. The results were elucidated based on the large changes in the transition and permanent dipole moments and in terms of (i) EWG strength, (ii) degree of donor-acceptor charge transfer and (iii) electronic coupling between the arms. The 2PA results were eventually supported and confronted with theoretical DFT calculations of the two-photon transition oscillator strengths.

UV waveguides light fabricated in fluoropolymer CYTOP by femtosecond laser direct writing

We have fabricated optical waveguides inside the UV-transparent polymer, CYTOP, by femtosecond laser direct writing for propagating UV light in biochip applications. Femtosecond laser irradiation is estimated to increase the refractive index of CYTOP by 1.7 x 10(-3) due to partial bond breaking in CYTOP. The waveguide in CYTOP has propagation losses of 0.49, 0.77, and 0.91 dB/cm at wavelengths of 632.8, 355, and 266 nm, respectively.

Laser drilling of nano-pores in sandwiched thin glass membranes

We report on a novel method of using an excimer laser to drill ultra-small pores in borosilicate glass membranes. By introducing a thin layer of liquid between sandwiches of two glass slides, we can shrink the pore size and smoothen the surface on the exit side. We are able to push the minimal exit pore diameter down to 90 nm, well below the laser wavelength of 193 nm. This is achieved with substrates over 150 microm thick. Compared to other methods, this technique is fast, inexpensive, and produces high quality smooth pores.

Large enhancement of femtosecond laser micromachining speed in dye-doped hydrogel polymers

Ophthalmologic hydrogel polymers are doped with Fluorescein or Coumarin dyes prior to the femtosecond laser micromachining process. We find that the achievable micromachining writing speed can be greatly increased while maintaining large refractive index changes (up to +0.08). Compared with previous results in dye-doped polymers that do not contain water such as PMMA, we obtain much larger index changes and much faster writing speeds.

Large enhancement of femtosecond laser micromachining speed in dye-doped hydrogel polymers

Ophthalmologic hydrogel polymers are doped with Fluorescein or Coumarin dyes prior to the femtosecond laser micromachining process. We find that the achievable micromachining writing speed can be greatly increased while maintaining large refractive index changes (up to +0.08). Compared with previous results in dye-doped polymers that do not contain water such as PMMA, we obtain much larger index changes and much faster writing speeds.

Femtosecond laser micromachining of waveguides in silicone-based hydrogel polymers

By tightly focusing 27 fs laser pulses from a Ti:sapphire oscillator with 1.3 nJ pulse energy at 93 MHz repetition rate, we are able to fabricate optical waveguides inside hydrogel polymers containing approximately 36% water by weight. A tapered lensed fiber is used to couple laser light at a wavelength of 632.8 nm into these waveguides within a water environment. Strong waveguiding is observed due to large refractive index changes. A large waveguide propagation loss is found, and we show that this is caused by surface roughness which can be reduced by optimizing the waveguides.