Multiplexed direct-frequency-comb Vernier spectroscopy of carbon dioxide 2ν1 + ν3 ro-vibrational combination band.

We investigated a set of nineteen 12C16O2 transitions of the 2ν1 + ν3 ro-vibrational band in the spectral region from 5064 to 5126 cm-1 at different pressures, using frequency-comb Vernier spectroscopy. Our spectrometer enabled the systematic acquisition of molecular absorption profiles with high precision. Spectroscopic parameters, namely, transition frequency, linestrength, and self-pressure broadening coefficient, have been accurately determined by using a global fit procedure. These data are in agreement with theoretical values contained in HITRAN2016 database [I. E. Gordon et al., J. Quant. Spectrosc. Radiat. Transfer 203, 3-69 (2017)] at the same precision level. A moderate improvement of the line intensity determinations, by a factor 1.5 in the best case [P(10) transition at 5091.6 cm-1], should be noticed, projecting direct-comb-Vernier-spectroscopy as an adequate tool for spectral intensity calibration.

Determination of the Boltzmann constant by means of precision measurements of H2(18)O line shapes at 1.39 µm.

We report on a new implementation of Doppler broadening thermometry based on precision absorption spectroscopy by means of a pair of offset-frequency locked extended-cavity diode lasers at 1.39 µm. The method consists in the highly accurate observation of the shape of the 4(4,1)→4(4,0) line of the H2(18)O ν1+ν3 band, in a water vapor sample at thermodynamic equilibrium. A sophisticated and extremely refined spectral analysis procedure is adopted for the retrieval of the Doppler width as a function of the gas pressure, taking into account the Dicke narrowing effect, the speed dependence of relaxation rates, and the physical correlation between velocity-changing and dephasing collisions. A spectroscopic determination of the Boltzmann constant with a combined (type A and type B) uncertainty of 24 parts over 10(6) is reported. This is the best result obtained so far by means of an optical method. Our determination is in agreement with the recommended CODATA value.

Analysis of the feed-forward method for the referencing of a CW laser to a frequency comb.

We report on a comprehensive theoretical and experimental analysis of the feed-forward method for external frequency stabilization of a continuous wave laser against a frequency comb. Application of the method to a distributed feedback diode laser at 1.55 µm allows line narrowing from 800 to 10 kHz, with frequency noise reduction by more than 2 decades up to a Fourier frequency of 100 kHz and a maximum control bandwidth of 0.8 MHz. The results are consistent with a relative phase fluctuation of 1.4 rad rms, as limited by uncompensated high-frequency noise of the slave laser.

Wide-bandwidth phase lock between a CW laser and a frequency comb based on a feed-forward configuration.

Wide-bandwidth phase lock between the tooth of a frequency comb and a CW extended-cavity diode laser at 1.55 µm is achieved by the use of an acousto-optical frequency shifter in a feed-forward configuration. The coherence properties of the comb are efficiently transferred to the CW laser, whose linewidth is narrowed down to the ∼10 KHz comb level. A maximum control bandwidth of ∼0.6 MHz has been experimentally achieved, limited by the transit time of the acoustic wave inside the frequency shifter.

High-precision molecular interrogation by direct referencing of a quantum-cascade-laser to a near-infrared frequency comb.

This work presents a very simple yet effective way to obtain direct referencing of a quantum-cascade-laser at 4.3 µm to a near-IR frequency-comb. Precise tuning of the comb repetition-rate allows the quantum-cascade-laser to be scanned across absorption lines of a CO2 gaseous sample and line profiles to be acquired with extreme reproducibility and accuracy. By averaging over 50 acquisitions, line-centre frequencies are retrieved with an uncertainty of 30 kHz in a linear interaction regime. The extension of this methodology to other lines and molecules, by the use of widely tunable extended-cavity quantum-cascade-lasers, paves the way to a wide availability of high-quality and traceable spectroscopic data in the most crucial region for molecular detection and interrogation.

Gene-gene interaction between CD40 and CD40L reduces bone mineral density and increases osteoporosis risk in women.

SUMMARY: We have analysed the association of single-nucleotide polymorphisms (SNPs) in CD40 and CD40L genes with bone mineral density (BMD) in our women. Results showed that women with TT genotype for rs1883832 (CD40) and for rs1126535 (CD40L) SNPs displayed reduced BMD and increased risk for osteopenia/osteoporosis. Our data notwithstanding, the results need to be replicated. INTRODUCTION: Recent data have revealed that the CD40/CD40L system can be implicated in bone metabolism regulation. Moreover, we previously demonstrated that rs1883832 in the CD40 gene was significantly associated with BMD and osteoporosis risk. The objective of the present work was to determine whether polymorphisms in CD40 and CD40L genes are associated with BMD and osteoporosis risk. METHODS: We conducted an association study of BMD values with SNPs in CD40 and CD40L genes in a population of 811 women of which 693 and 711 had femoral neck (FN) and lumbar spine (LS) densitometric studies, respectively. RESULTS: Women with the TT genotype for rs1883832 (CD40) showed a reduction in FN-BMD (P = 0.005) and LS-BMD (P = 0.020) when compared with women with the CC/CT genotype. Moreover, we found that rs1126535 (CD40L) was significantly associated with LS-BMD so that women with the TT genotype displayed lower BMD (P = 0.014) than did women with the CC/CT genotype. Interestingly, we have found a strong interaction between polymorphisms in these genes. Thus, women with the TT genotype for both rs1883832 and rs1126535 SNPs (TT + TT women) showed a lower age-adjusted BMD (Z-score) for FN (P = 0.0007) and LS (0.007) after adjusting by years since menopause, body mass index, smoking and menopausal status, densitometer type, hormone replacement therapy (HRT) use and HRT duration and after making the Bonferroni adjustment for multiple comparisons than did the remaining women. Logistic regression analysis adjusted by these covariates showed that TT + TT women had increased risk for FN (odds ratio (OR) = 2.76; P = 0.006) and LS (OR = 2.39; P = 0.020) osteopenia or osteoporosis than did the other women. CONCLUSIONS: Our results suggest that interaction between genetic variants in the CD40 and CD40L genes exerts a role on BMD regulation. Further studies, which we welcome, are needed to replicate these data in other populations.

Absolute frequency spectroscopy of CO2 lines at around 2.09 µm by combined use of an Er:fiber comb and a Ho:YLF amplifier.

The low-frequency tail of an octave-spanning supercontinuum (SC) generated by an Er:fiber comb is enhanced by a multipass Ho:YLF amplifier and used in a sum-frequency-generation scheme to obtain absolute referencing of a single-mode Tm-Ho:YAG laser tunable around 2.09 µm. By tuning the comb repetition frequency, the probing laser is scanned across the absorption lines of a CO(2) gas sample and highly accurate absorption profiles are measured. This approach can be readily scaled to any wavelength above ~2 µm.

CW and femtosecond operation of a diode-pumped Yb:BaY(2)F(8) laser.

We report for the first time on laser action of a diode-pumped Yb:BaY(2)F(8) crystal. Both CW and femtosecond operations have been demonstrated at room-temperature conditions. A maximum output power of 0.56 W, a slope efficiency of 34%, and a tunability range from 1013 to 1067 nm have been obtained in CW regime. Transform-limited pulse trains with a minimum duration of 275 fs, an average power of 40 mW, and a repetition rate of 83 MHz have been achieved in a passive mode-locked regime using a semiconductor saturable absorber mirror.

Femtosecond laser written optical waveguide amplifier in phospho-tellurite glass.

We report on the first demonstration of an optical waveguide amplifier in phospho-tellurite glass providing net gain at 1.5 µm. The device was fabricated using a high repetition rate femtosecond laser and exhibited internal gain across 100-nm bandwidth covering the entire C + L telecom bands.

Fiber strain sensor based on a pi-phase-shifted Bragg grating and the Pound-Drever-Hall technique.

A fiber strain sensor based on a p-phase-shifted Bragg grating and an extended cavity diode laser is proposed. Locking the laser frequency to grating resonance by the Pound-Drever-Hall technique results in a strain power spectral density S(epsilon) (f) = (3 x 10(-19) f(-1) +2.6 x 10(-23)) epsilon(2)/Hz in the Fourier frequency range from 1 kHz to 10 MHz (epsilon being the applied strain), corresponding to a minimum sensitivity of 5 pepsilon Hz(-1/2) for frequencies larger than 100 kHz.

Diode-pumped passively mode-locked Yb:YLF laser.

We demonstrate passive mode-locking by means of a semiconductor saturable-absorber mirror in a diode-pumped Yb:YLF laser. We present crystal growth process, spectroscopic measurements, and investigation of mode-locking performance. Pulse trains with minimum duration of 196 fs, average power of 54 mW and a repetition rate of 55 MHz were obtained. The optical spectrum, centered at 1028 nm, has a 7.1-nm bandwidth leading to nearly transform-limited pulses.

Experimental demonstration of the optical Zeno effect by scanning tunneling optical microscopy.

An experimental demonstration of a classical analogue of the quantum Zeno effect for light waves propagating in engineered arrays of tunneling-coupled optical waveguides is reported. Quantitative mapping of the flow of light, based on scanning tunneling optical microscopy, clearly demonstrates that the escape dynamics of light in an optical waveguide side-coupled to a tight-binding continuum is slowed down when projective measurements, mimicked by sequential interruptions of the decay, are performed on the system.

Active waveguides written by femtosecond laser irradiation in an erbium-doped phospho-tellurite glass.

We report on fs-laser micromachining of active waveguides in a new erbium-doped phospho-tellurite glass by means of a compact cavity-dumped Yb-based writing system. The spectroscopic properties of the glass were investigated, and the fs-laser written waveguides were characterized in terms of passive as well as active performance. In particular, internal gain was demonstrated in the whole C+L band of optical communications (1530- 1610 nm).

Sub-100 fs pump-probe spectroscopy of Single Wall Carbon Nanotubes with a 100 MHz Er-fiber laser system.

An extremely compact and versatile near-infrared two-color femtosecond pump-probe spectroscopy apparatus based on an amplified Erfiber laser system is presented and applied to the characterization of the relaxation dynamics of single-wall carbon nanotubes with fundamental absorption in the 2 microm spectral region. By implementing a fast-scan technique, dynamics as long as 3 ps are acquired in 5 s with a relative sensitivity of 10(-4) and a temporal resolution below 100 fs at 2 microm.

1.5 mum single longitudinal mode waveguide laser fabricated by femtosecond laser writing.

A compact and efficient single longitudinal mode laser based on a femtosecond laser written waveguide is demonstrated. A maximum output power exceeding 50 mW was measured in single longitudinal and transverse mode operation, with 21% slope efficiency. The active waveguide was fabricated on erbium-ytterbium-doped phosphate glass by direct writing with femtosecond laser pulses from a diode-pumped cavity-dumped oscillator.

Quantitative Phase Microscopy of microstructures with extended measurement range and correction of chromatic aberrations by multiwavelength digital holography.

Quantitative Phase Microscopy (QPM) by interferometric techniques can require a multiwavelength configuration to remove 2pi ambiguity and improve accuracy. However, severe chromatic aberration can affect the resulting phase-contrast map. By means of classical interference microscope configuration it is quite unpractical to correct such aberration. We propose and demonstrate that by Digital Holography (DH) in a microscope configuration it is possible to clear out the QPM map from the chromatic aberration in a simpler and more effective way with respect to other approaches. The proposed method takes benefit of the unique feature of DH to record in a plane out-of-focus and subsequently reconstruct numerically at the right focal image plane. In fact, the main effect of the chromatic aberration is to shift differently the correct focal image plane at each wavelength and this can be readily compensated by adjusting the corresponding reconstruction distance for each wavelength. A procedure is described in order to determine easily the relative focal shift among different imaging wavelengths by performing a scanning of the numerical reconstruction along the optical axis, to find out the focus and to remove at the same time the chromatic aberration.

Effects of laser irradiation on hematoporphyrin-treated normal and transformed thyroid cells in culture.

Laser irradiation of tissues treated in vivo with the hematoporphyrin derivative (HPD) is known to result in a cytocidal effect, reportedly more pronounced in the tumor than in the surrounding normal tissues. In order to ascertain if this phenomenon had a clear cellular basis, it has been now reproduced in vitro in a model system consisting of normal and transformed cell lines. Epithelial rat thyroid cells were infected and transformed with a RNA oncogenic virus. Both the original (normal) and the viral-transformed (tumorigenic) cells were incubated with HPD and exposed to two types of laser irradiation: 631 nm, continuous wave; and 337.1 nm, pulsed. Under the conditions tested, the percentage survival of the transformed cells was found to be lower (up to approximately 3 times) than that of the normal cells. The cytocidal effect was greater using the pulsed than using the continuous-wave irradiation. The difference between normal and tumor cells was more evident at 30 micrograms than at 50 micrograms of HPD per ml. The HPD not followed by laser irradiation had no effect on the cell growth rate. The findings of a significant difference in the sensitivity to photoactivated HPD between normal and tumor cells under strictly controlled and highly comparable conditions opens new possibilities to the study of the cellular and molecular mechanisms involved in the phototherapy of tumors. Furthermore, studies in vitro on the active components of the photosensitizer and on their selectivity towards the tumor cells, explained at a cellular level, will lead to better approaches to photochemotherapy in vivo.

[Cormobidity of sensorineural hearing loss and other autoimmune diseases. Usefulness of laboratory tests]. / Estudio de comorbilidad de la hipoacusia neurosensorial y otras enfermedades de patogenia autoinmune. Utilidad de las pruebas de laboratorio.

OBJECTIVES: To value if the sensorineural hearing loss (SHL) in several autoimmune diseases (AD) is also secondary to immunomediation. PATIENTS AND METHODS: In 342 cases with SHL and any AD and 301 normoacoustic controls with AD a non-specific immunologic battery of tests and a Western-blot (WB) for anticochlear autoantibodies were developed, and cases with SHL were treated with deflazacort. RESULTS: Alterations in non-specific battery were similar between cases and controls. But a 12,5% of cases with SHL and a 1,6% of normoacoustic showed a positive WB (p<0,001). Steroid therapy improved hearing in 14,3% of cases. In them, sensitivity and specificity of non-specific battery were 78,4% and 75,5%, respectively, to predict response to therapy. These were 98,9% and 81,6% for WB. CONCLUSIONS: The SHL in cases with AD can be considered immunomediated in a discrete average, but the diagnostic efficiency of WB to predict an improvement after steroid therapy is high.

Optical properties of waveguides written by a 26 MHz stretched cavity Ti:sapphire femtosecond oscillator.

We report on the fabrication, by a 26 MHz stretched-cavity femtosecond Ti:sapphire oscillator, of optical waveguides in different glass substrates, and their optical characterization. Operation of these waveguides in the telecom range at 1.55 microm is demonstrated. Digital holography microscopy is used to measure their refractive index profile. The results evidence a strong dependence of the fabrication process on the glass matrix.

C-band waveguide amplifier produced by femtosecond laser writing.

An optical waveguide amplifier fabricated on erbium-ytterbium-doped phosphate glass by direct femtosecond laser writing is demonstrated. The waveguides are manufactured using 1040-nm radiation from a diode-pumped cavity-dumped Yb:KYW oscillator, operating at a 885 kHz repetition rate, with a 350 fs pulse duration. Peak internal gain of 9.2 dB is obtained at 1535 nm, with a minimum internal gain of 5.2 dB at 1565 nm. Relatively low insertion losses of 1.9 dB enable for the first time an appreciable net gain in the full C-band of optical communications.