Enhanced and broadened SRS spectra of toluene mixed with chloroform in liquid-core fiber

Intermolecular energy transfer-enhanced super-broadband stimulated Raman scattering in cyclohexane-benzene mixtures

Supercontinuum radiation has found numerous applications in diverse fields encompassing spectroscopy, pulse compression, and tunable laser sources. Anomalous enhanced stimulated Raman scattering (SRS) of cyclohexane-benzene mixtures was obtained in this study. SRS of the pure solvent, the multi-order Stokes of the strongest fundamental vibration modes, and energy transfer in intra-molecular modes were observed. SRS of the mixture revealed that the cross-pumping effect was generated between the C-H stretching (v₂) mode of cyclohexane and the C=C ring skeleton (v₁) mode of benzene, thereby producing the intermolecular secondary stimulated Raman emission and the appearance of two super-broadband radiations at 664.36-673.9 nm and 704.62-729.22 nm. The results suggest that the energy transfer of intermolecular vibrational modes, where the strongest vibrational mode excites other vibrational modes, is a simple approach for generating supercontinuum coherent radiation.

Generation of dual-supercontinuum coherent radiation in acetone mixed with carbon disulfide by stimulated Raman scattering

Stimulated Raman scattering (SRS) in a liquid has been a major focus of nonlinear optics. Traditional SRS generates single or cascaded Stokes components arising from spontaneous Raman noise. Herein, we report the formation mechanism of a specific spectrum-continuous spectroscopy technique based on SRS of mixed liquids. SRS of a mixed acetone and carbon disulfide solution is investigated by a pulsed Nd:YAG laser with a wavelength of 532 nm. Two remarkably asymmetric broadened SRS lines are obtained. When the volume ratio is 7:3, the broadened spectral bands are optimized. The supercontinuum spectroscopy phenomenon is explained by hydrogen bond formation, adjacent vibrational modes coupling, and laser-induced plasma generation. This technique has the potential to contribute to the development of a supercontinuum Raman laser.

Carbon chloride-core fibers for soliton mediated supercontinuum generation

We report on soliton-fission mediated infrared supercontinuum generation in liquid-core step-index fibers using highly transparent carbon chlorides (CCl₄, C₂Cl₄). By developing models for the refractive index dispersions and nonlinear response functions, dispersion engineering and pumping with an ultrafast thulium fiber laser (300 fs) at 1.92 μm, distinct soliton fission and dispersive wave generation was observed, particularly in the case of tetrachloroethylene (C₂Cl₄). The measured results match simulations of both the generalized and a hybrid nonlinear Schrödinger equation, with the latter resembling the characteristics of non-instantaneous medium via a static potential term and representing a simulation tool with substantially reduced complexity. We show that C₂Cl₄ has the potential for observing non-instantaneous soliton dynamics along meters of liquid-core fiber opening a feasible route for directly observing hybrid soliton dynamics.

Stimulated Raman-Kerr scattering in an integrated nonlinear optofluidic fiber arrangement

We describe a novel optofluidic fiber arrangement that allows for nonlinear effects enhancement between fluids and laser light while suppressing the generation of cavitation bubbles. By filling this optofluidic system with toluene and pumping it with a nanosecond microchip laser, we demonstrate the efficient generation of a broadband Raman frequency comb spanning from 532 to more than 1000 nm. It is further shown that the Raman frequency comb dramatically broadens toward broadband continuum light due to the stimulated Raman-Kerr scattering.

Integrated hollow-core fibers for nonlinear optofluidic applications

A method to fabricate all-in-fiber liquid microcells has been demonstrated which allows for the incorporation of complex hollow-core photonic crystal fibers (HCPCFs). The approach is based on a mechanical splicing method in which the hollow-core fibers are pigtailed with telecoms fibers to yield devices that have low insertion losses, are highly compact, and do not suffer from evaporation of the core material. To isolate the PCF cores for the infiltration of low index liquids, a pulsed CO2 laser cleaving technique has been developed which seals only the very ends of the cladding holes, thus minimizing degradation of the guiding properties at the coupling region. The efficiency of this integration method has been verified via strong cascaded Raman scattering in both toluene (high index) core capillaries and ethanol (low index) core HCPCFs, for power thresholds up to six orders of magnitude lower than previous results. We anticipate that this stable, robust all-fiber integration approach will open up new possibilities for the exploration of optofluidic interactions.

UV-curable liquid-core fiber lenses with controllable focal length

Lensed fiber optics is of great importance to many applications such as optical sensing, optical coupling, laser trapping etc. In this paper we have demonstrated a unique method to fabricate liquid-core lensed fibers by filling UV curable adhesive into hollow fibers, and to control the focal length and spot size by pumping liquid into or out of the fiber end. In experiment, tuning of focal length from 2.414 to 0.810 mm has been obtained, and solidification of the adhesive core has also been carried out successfully. Further simulation suggests that the focused spot size can be reduced to <10 micron by adjusting the refractive index and fiber geometry. Such technique has the potential to manufacture custom-made solid lensed fibers and liquid-core solid-tip lensed fibers in volume at low cost. The same technique may be used for input and output coupling of optofluidic waveguides with external optical components like optical fibers and lasers.