Two-photon and Three-photon Fluorescence of Triton X-100 in the Ultraviolet Region.

We report, to our best knowledge, the first observation of two-photon and three-photon fluorescence of Triton X-100 (TX-100) in water and cyclohexane. The observed multiphoton fluorescence (MF) falls in the ultraviolet region 280-340nm as its one photon fluorescence does. Effects of excitation wavelengths and solution concentrations on the fluorescence spectra are investigated. We found the optimal excitation wavelength and solution concentration to obtain the strongest MF. For relatively weaker three-photon fluorescence, there exists fluctuation in its spectrum due to its small SNR. The peak wavelength is around 300nm and only varies slightly with the solution concentration, solvent type, and excitation wavelength, which is quite different from those of other luminophors. This work has extended the wave band of MF to the purple and ultraviolet regions of 280-340nm and study of TX-100 to nonlinear optics field. The results may be potentially applied in ultraviolet MF detection and in manufacturing ultraviolet multiphoton laser in the future. Although for the latter case, there is still a long way to go to enhance its fluorescence efficiency and cross section of stimulated emission beforehand.

Two-Photon Fluorescence Study of Olive Oils at Different Excitation Wavelengths.

Two-photon fluorescence (TPF) of olive oils is discovered and observed experimentally for the first time. Variations of the single-photon fluorescence (SPF) and TPF with the excitation wavelength are investigated for four different olive oils. The results show that fluorescence of the cosmetic olive oils (COO) is very weak and exhibits only one spectral peak around 490 nm. While for the ordinary edible oils (OEO) whether they are during their shelf life or not, their fluorescence spectra may exhibit multiple peak structures. The short-term natural expiration only slightly weakens TPF of OEO. Moreover, the excitation wavelength affects the OEO spectra considerably in terms of the spectral peak number, the spectral peak position, and spectral shapes. When the excitation wavelength decreases from 700 nm, the whole TPF of the OEO also decreases. Relatively, however, the short wave band will decrease and disappear more quickly. While for the SPF, the long wave band will decrease and disappear first. The optimal excitation wavelengths to make the TPF strongest are around 700 nm and 640 nm for OEOs and COO, respectively. And effects of temperature on SPF and TPF of extra virgin olive oil are also explored. This work may be of significance for its potential applications in TPF detection and two-photon laser.

Experimental study of optical hyperbolic metamaterials for high-efficiency spatial filtering.

We experimentally study the optical properties of Al-SiO2 hyperbolic metamaterials. The hyperbolic dispersion and ultrathin Al film ∼12nm make the Al-SiO2 multilayers possess transmission efficiency ∼0.3 for the spatial frequency ranging from k0 to 1.42 k0 at 363.8 nm illumination. The atomic concentration of 3% Cu-doping is experimentally demonstrated to obtain Al film ∼12nm with root-mean-square roughness ∼0.49nm. The fabricated Al-SiO2 multilayers combined with the optimized ZrO2 resonant grating with period 280 nm serves as a structured illumination device, which efficiently converts the P-polarized normal field to the spatial frequency 1.3 k0 structured field. The measured average transmission intensity of the ±1 order is ∼0.14, and the intensity ratio of the ±1 order and 0 order is ∼65. This Letter is promising for structured illumination, spontaneous emission enhancement, Cherenkov radiation, etc.

Exciting Wavelength and Concentration Related Two-Photon Fluorescence of Single and Mixed Laser Dyes.

Two-photon nonlinear process induced fluorescence of Rhodamine 6G (R6G), Rhodamine B (RB), and their mixed aqueous solutions in mass proportion of 1:1, is experimentally observed by different exciting wavelengths. It shows that, for each sample, the exciting wavelength can influence the fluorescence intensity considerably but only slightly influence the peak wavelength of the spectrum. The optimal exciting wavelengths of R6G and the mixed dyes are around 700 nm. While for RB, the optimal exciting wavelengths can be 700 nm and 620 nm. For each dye sample, the spectral red-shift will occur as increase of the solution concentration. The mixing of the two dyes will cause the spectral red-shift with regard to the single dye under our experimental conditions. Moreover, in comparison, at lower concentrations, the mixed dye has relatively intense fluorescence. This work is of significance for determining the optimal exciting wavelength and developing the tunable two-photon dye lasers.

Dye-enhanced third upconversion Raman overtone in the ultraviolet region under intense excitation of a 532 nm laser.

We report, to our best knowledge, the first observation of enhanced third upconversion Raman overtone of water in the ultraviolet region 240-380 nm by Rhodamine 6G (R6G) under intense excitation of a 532 nm laser. Its spectral peak is mostly around 288 nm. This ultraviolet spectrum has also been obtained for purified water on the Raman spectrometer LRS-3 and fluorescence spectrometer RF-5301PC, which have photomultiplier tubes. The spectral profile is approximately a triangle in most cases. Moreover, an intense and broad background is also observed to appear in the spectrum. Additionally, the conventional visible luminescence spectrum of R6G is discovered to coexist with the ultraviolet one. In comparison, the visible spectrum is much more intense.

Generation of single or double parallel breathing soliton pairs, bound breathing solitons, moving breathing solitons, and diverse composite breathing solitons in optical fibers.

Interactions of two truncated Airy pulses with arbitrarily initial relative phases, initial pulse intervals, and different soliton order are numerically investigated in optical fibers. When the soliton order is 1, depending on different initial pulse intervals, the initial in-phase Airy pulses may evolve to single breathing solitons, bound breathing solitons, and single parallel breathing solitons. While the out-of-phase Airy pulses may evolve to parallel or repulsive soliton pairs with breathing or weak breathing, after radiating away some dispersive waves. When the initial relative phases take arbitrary values except 0 and π, moving single breathing solitons and repulsive or parallel soliton pairs will form. Moreover, the whole temporal profiles may become asymmetric. The repulsive soliton pairs consist of two moving breathing solitons with different intensities, moving velocities, and breathing periods. The most interestingly is that, when the soliton order is larger than one, we observe double bound breathing solitons, double parallel breathing soliton pairs, and diverse composite breathing solitons which consist of two or more different breathing solitons. one can effectively manipulate and select the soliton expected and its evolution dynamics by adjusting the soliton order, initial pulse intervals, and initial relative phases.

Evolution of finite energy Airy pulses and soliton generation in optical fibers with cubic-quintic nonlinearity.

We numerically simulate the propagation of finite energy Airy pulses in optical fibers with cubic-quintic nonlinearity and analyze the effects of quintic nonlinear parameters and soliton order number on their evolution properties. The soliton pulses are observed, whose peak amplitudes and corresponding temporal positions will vary with the propagation distance. Depending on different quintic nonlinearity parameters and soliton order number, the soliton pulse temporal positions exhibit weak decayed oscillations and then nearly linearly shift to leading or trailing edge of the Airy wavepacket, or tend to fixed positions, and the peak amplitudes also exhibit decayed oscillations but with different oscillation amplitude and central values. For large soliton order number, the soliton pulses are considerably compressed. Other weak dispersive wave pulses will appear near the main soliton pulses and gradually depart from the main soliton pulses. In the case of small soliton order, despite their considerable energy attenuation, the main lobes and even minority of the neighboring side lobes of the Airy pulses can still recover from the energy transfer to the soliton pulses and the dispersive wave pulses and maintain their unique properties of self-healing and self-acceleration in time for a very long distance. In the case of large soliton order, however, the Airy wavepacket only remains its very weak background and even disappears quickly.