Effect of ambient air on femtosecond laser ablation of highly oriented pyrolytic graphite.

Highly oriented pyrolytic graphite is ablated by femtosecond laser in air and vacuum, respectively. The morphologies and material components of the ablated target surface are examined by scanning electron microscopy and micro-Raman spectroscopy. For laser fluence no less than 0.5 J/cm(2), the laser-induced periodic surface grooves formed in air are found to be much less clearer than those formed in vacuum; beneath the amorphous carbon debris, the surface ablated in air is composed of nanocrystalline graphite, but in vacuum it retains the ordered graphite structure. The thermal relaxation of the ablated target induced by air-assisted heat transfer is considered to be the main reason for the differences. The transportation of air molecules along the surface, the classical size effect of heat conduction and high solid-air heat transfer coefficient in nanoscale enhance the air-assisted heat transfer.

Super-luminescent jet light generated by femtosecond laser pulses.

Phenomena of nonlinear light-matter interaction that occur during the propagation of intense ultrashort laser pulses in continuous media have been extensively studied in ultrafast optical science. In this vibrant research field, conversion of the input laser beam into optical filament(s) is commonly encountered. Here, we demonstrate generation of distinctive single or double super-luminescent optical jet beams as a result of strong spatial-temporal nonlinear interaction between focused 50 fs millijoule laser pulses and their induced micro air plasma. Such jet-like optical beams, being slightly divergent and coexisting with severely distorted conical emission of colored speckles, are largely different from optical filaments, and obtainable when the focal lens of proper f-number is slightly tilted or shifted. Once being collimated, the jet beams can propagate over a long distance in air. These beams not only reveal a potentially useful approach to coherent optical wave generation, but also may find applications in remote sensing.

Control of periodic ripples growth on metals by femtosecond laser ellipticity.

Formation of the periodic ripples on metallic surfaces is investigated comprehensively using variable ellipticities of femtosecond lasers. Compared with the linearly polarized incidence, the well defined grating-like ripple structures rather than the uniform arrays of nanoparticle can always be obtained for the elliptical polarization lasers. The ripple orientation is slanted clockwise or anticlockwise depending on the laser helicity but always display a maximum angle of 45°. Theoretical analyses indicate that no circular polarization is achieved for femtosecond lasers passing through quarter waveplate, and the induced ripple orientation is determined by the major axis of the polarization ellipse. The simulation results agree well with the experimental observations.

Characteristics of micro air plasma produced by double femtosecond laser pulses.

Dynamic characteristics of air plasma generated by focused double collinear femtosecond laser pulses with a time interval of 10 ns are experimentally investigated. The air plasma emission changes significantly when altering the energy ratio between the two laser pulses. Time-resolved shadowgraphic measurements reveal that a small volume of transient vacuum is formed inside the air shock wave produced by the first laser pulse, which causes the second laser pulse induced ionization zone to present as two separate sections in space. Also recorded is strong scattering of the second laser pulse by the ionized air just behind the ionization front of the first laser pulse produced shock wave. Due to the high intensity of the scattered light, coherent Thomson scattering enhanced by plasma instabilities is believed to be the main scattering mechanism in this case.

Low-loss channel optical waveguide fabrication in Nd(3+)-doped silicate glasses by femtosecond laser direct writing.

Optical waveguides were fabricated in neodymium-doped silicate glass by using a low-repetition-rate (1 kHz) femtosecond laser inscription. Two different types of waveguide structure are fabricated. In the first, guiding occurs in the focal spot. In the second, guiding occurs in the region between the two filaments. The near-field intensity distribution, propagation loss, index profile reconstruction, and calculation of the modal intensity distribution by the beam propagation method of these waveguides are presented. On the basis of near-field intensity distribution of the light guided through the waveguides and the propagation loss measurement, the optimum writing conditions such as the pulse energy and scan velocity were determined. The waveguide written with 2.2 µJ pulse energy and 50 µm/s scan velocity shows strong guidance at 632.8 nm, with an index contrast of 7 × 10(-4) and a propagation loss of ~0.8 dB/cm.

Investigation of ultrashort pulse laser ablation of solid targets by measuring the ablation-generated momentum using a torsion pendulum.

50 fs - 12 ps laser pulses are employed to ablate aluminum, copper, iron, and graphite targets. The ablation-generated momentum is measured with a torsion pendulum. Corresponding time-resolved shadowgraphic measurements show that the ablation process at the optimal laser fluence achieving the maximal momentum is primarily dominated by the photomechanical mechanism. When laser pulses with specific laser fluence are used and the pulse duration is tuned from 50 fs to 12 ps, the generated momentum firstly increases and then remains almost constant, which could be attributed to the change of the ablation mechanism involved from atomization to phase explosion. The investigation of the ablation-generated momentum also reveals a nonlinear momentum-energy conversion scaling law, namely, as the pulse energy increases, the momentum obtained by the target increases nonlinearly. This may be caused by the effective reduction of the dissipated energy into the surrounding of the ablation zone as the pulse energy increases, which indicates that for femtosecond laser the dissipated energy into the surrounding target is still significant.

Surface microstructuring of Ti plates by femtosecond lasers in liquid ambiences: a new approach to improving biocompatibility.

Microstructuring of Ti plates with femtosecond laser pulses is investigated in three different liquids. In these ambiences, complex microstructures with voids and islands are produced on the sample surfaces, whose feature sizes are controlled by the laser parameters. Through adopting supersaturated Hydroxyapatite suspension with higher incident laser fluences, it is for the first time to observe the firm deposition of biocompatible elements Ca-P on the microstructures. At lower laser fluence, only porous structure is present but without additional elements deposition. Both plasma-related ablation under the confinement of liquids and micro-bubbles striking are employed to discuss such structures formation. Tight combining elements Ca-P onto the structured surfaces provide a new way to improve the biocompatibility of body-embedded devices.

Deconvolution methods for image deblurring in optical coherence tomography.

Two-dimensional deconvolution methods are proposed to deblur optical coherence tomography images. One employs a two-dimensional deconvolution with a matrix given by the product of the longitudinal and transversal point-spread functions as its kernel, which can be taken as the general point-spread function of an optical coherence tomography system. The other uses two one-dimensional deconvolutions with the longitudinal and transversal point-spread functions successively. It is shown that the two deconvolution methods can deblur the experimentally obtained optical coherence tomography images effectively.

Time-resolved shadowgraphs of material ejection in intense femtosecond laser ablation of aluminum.

The dynamic process of intense 50 fs laser ablation of aluminum is investigated by ultrafast time-resolved microscopy. A stripe pattern preceding phase explosion is clearly seen in the shadowgraph of 1 ns time delay. Intermittent material ejections are observed within the ejected plume after 2.5 and 7 ns time delay, respectively, which may be attributed to the material response to the generation of an extremely strong thermoelastic wave. Similar processes are also recorded in the ablation of silicon and glass samples, except for the glass samples, the intermittent material ejections are not found.

Experimental observation on spectrum evolution of femtosecond pulses in filamentation.

We present an experimental observation on spectrum evolution of femtosecond pulses in filamentation by introducing a hollow fiber as a probe and moving it along the filament. The results show that at a particular position of the filament, the pulse spectrum from the hollow fiber expands to its maximum, which corresponds to the shortest pulse duration existing in the filament. The influence of gas pressure on the spectrum broadening is also examined.

Dispersion of linearly polarized light propagating in a thin birefringent plate.

We analyze theoretically the dispersion of linearly polarized light propagating in a uniaxial anisotropic medium where multibeam interference is present. Explicit expressions of the group-delay dispersion for transmitting waves are derived for the simplest situation, and the effect of dispersion on pulse broadening is analyzed for a few selected cases. Our results reveal that at normal incidence and in the situation where the optic axis is parallel to the surface of birefringent plate (in the x-y plane), the dispersion of the refracted wave decreases with the extent of birefringence. In particular, the dispersion for the electric field parallel to the polarization direction of the incident light changes with the rotation angle between the optic axis and the polarization direction of the incident field, whereas the dispersion for the refracted field whose direction is vertical to the polarization of incident light is independent of this angle. For oblique incidence, dispersion varies substantially for different incident angles. In the situation where the optic axis is in the x-z plane at either normal or oblique incidence, the dispersion increases in a periodically oscillating manner as a function of the relative thickness of the birefringent plate.

[Olfactory function and olfactory marker protein in patients with chronic sinusitis].

OBJECTIVE: To study the pathogenesis of dysosphresia in patients with chronic sinusitis, to discuss the expression and significance of olfaction marker protein in olfactory mucosa. METHODS: There were 55 cases with chronic sinusitis in the experimental group, and 11 cases in the control. All of them were first tested by subjective method, and then the olfactory marker protein in olfactory mucosa was examined by the method of immunohistochemistry. Tissue sections were observed under optical microscope. RESULTS: The ratio of dysosphresia in patients with chronic sinusitis was 50.9% (28/55), while by subjective olfactory test, it was 85.5% (47/55). The ratio of dysosphresia in control patients was 9.09% (1/11), by subjective olfactory test, it was 18.2% (2/11). Olfactory marker protein was identified in the olfactory cells and microvillar cells by histochemical and immunohistochemical technique (S-P method). CONCLUSIONS: The main cause of dysosphresia in patients with chronic sinusitis is the decrease, atrophy and degeneration of the olfactory cells, which lead to the failure of olfactus perception and recognition.

[Research of the P substance on the olfactory mucous in sinusitis].

OBJECTIVE: To discuss the pathogenesis of dysosphresia in the chronic sinusitis patients. METHOD: Fifty-five cases with chronic sinusitis as experimental group, and 11 cases as control,mere analyzed with acidophilus monitor, and then the P substances in their olfactory mucous were detected. RESULT: The positive ratio is 50.9% in the chronic sinusitis patients with dysosphresia, acidophilus monitor in factory mucous was 89.1%. Furthermore, it showed the SP locating in the olfactory cells, support cells, basal cell, glands, epithelium cells of blood vessels, a few of lymphocytes and acidophilus by using the histochemical, immunohistochemical technique (S-P method). CONCLUSION: The allergy change of olfactory mucous is one of the main factors that draw olfactory function disorder.

Light propulsion of microbeads with femtosecond laser pulses.

Milli-Joule, femtosecond laser pulses have been used to propel microbeads for the first time. The microbeads of three different materials (iron, glass, and polystyrene) are used, weighting from 0.84 mg to 1.4 mg with a diameter range of 0.7-1.1 mm. Experimental parameters such as focused beam spot diameter, pulse energy, and pulse width are carefully varied to investigate their respective influences on the specific ablative laser propulsion. It is found that both the momentum coupling efficiency and the overall energy conversion efficiency from light energy to kinetic energy are greater for shorter laser pulses. A typical value of the momentum coupling efficiency of 5.0 dyne/W for iron beads is obtained. It is also evident that for metallic and non-metallic microbeads the momentum coupling efficiency has different variation tendencies versus the focused beam spot diameter.

[Relationship between expressions of GATA-3 and interleukin-5 in nasal polyps].

OBJECTIVE: To evaluate the role of transcription factor GATA-3 in the pathogenesis of nasal polyps. METHODS: The expression of GATA-3 was detected by immunohistochemistry and reverse transcriptase polymerase chain reaction (RT-PCR) in 28 cases of nasal polyps and 17 specimens of normal nasal epithelium. The expression of interleukin-5 (IL-5) in these specimens was detected by enzyme-linked immunosorbent assay (ELISA) meanwhile. RESULTS: Immunohistochemistry showed, as confirmed by RT-PCR, a positive rate of GATA-3 of 89.3% in the nasal polyp (25/28) and 29.4% in the normal nasal mucosa (5/17), P < 0.05. GATA-3 was mainly distributed in submucous inflammatory cells. The relative density ratio of GATA-3 to GAPDH was 0.618 +/- 0.137 in nasal polyp and 0.21 +/- 0.11 in normal nasal mucosa (P < 0.05) as indicated by RT-PCR and agarose electrophoresis. The concentrations of IL-5 were 69.4 +/- 15.1 pg/ml and 25.7 +/- 13.0 pg/mg in the two groups respectively. The expression of GATA-3 was positively correlated to the expression of IL-5 in the nasal polyp. CONCLUSION: Contributing to the overexpression of such cytokines as IL-5, GATA-3 may play an important role in the pathogenesis of nasal polyps.

[Analysis of growth model in vestibular aqueduct during human fetal development].

OBJECTIVE: To characterize the growth of the developing vestibular aqueduct in order to gain a better understanding of the possible origins of enlarged vestibular aqueduct. METHODS: Serial sections from 32 temporal bones for every other week from human embryos ranging in age from 6 to 38 weeks were studied with 3DMed medical image analysis software. The internal, external aperture, midpoint diameter and length vestibular aqueduct were analyzed with regression analysis to obtain a growth curve. RESULTS: The internal aperture of vestibular aqueduct was began to form at 6 weeks' gestation. It grew to reach the posterior surface of the petrous bone in the posterior cranial fossa by 10 weeks' gestation. All width parameter mean value in our embryos nerve reached the maximum average width in the adult. Statistical analysis showed that the vestibular aqueduct grew in a nonlinear continuous fashion and instability trend throughout embryonic life, except length parameter. CONCLUSION: The vestibular aqueduct grows in a nonlinear fashion throughout embryonic life. The widest aqueduct measured in embryonic life does not reach the maximum average width in the adult. These results suggest that it would be possible for vestibular aqueduct to develop postnatally.