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.

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.

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.

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.

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.

Experimental observation of a photon bouncing ball.

An optical analogue of a quantum particle bouncing on a hard surface under the influence of gravity (a quantum bouncer) is experimentally demonstrated using a circularly curved optical waveguide. Spatially resolved tunneling optical microscopy measurements of multiple beam reflections at the waveguide edge clearly show the appearance of wave packet collapses and revivals (either integer and fractional), corresponding to the full quantum regime of the quantum bouncer.

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).

Diode-pumped single-frequency Tm:LiLuF(4) ring laser.

We report a room-temperature single-frequency Tm:LiLuF(4) laser with a maximum output power of 120 mW, a slope efficiency of 13%, and a wavelength tunability range from 1875 to 1895 nm. Both frequency and relative intensity noise have been investigated, showing an emission linewidth of approximately 300 kHz over 1 ms observation time and an intensity noise spectrum limited by quantum noise for Fourier frequencies larger than 5 MHz.

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.

Primary gas thermometry by means of laser-absorption spectroscopy: determination of the Boltzmann constant.

We report on a new optical implementation of primary gas thermometry based on laser-absorption spectrometry in the near infrared. The method consists in retrieving the Doppler broadening from highly accurate observations of the line shape of the R(12) nu1+2nu2(0)+nu3 transition in CO2 gas at thermodynamic equilibrium. Doppler width measurements as a function of gas temperature, ranging between the triple point of water and the gallium melting point, allowed for a spectroscopic determination of the Boltzmann constant with a relative accuracy of approximately 1.6 x 10(-4).

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.

A C >T polymorphism located at position -1 of the Kozak sequence of CD40 gene is associated with low bone mass in Spanish postmenopausal women.

UNLABELLED: This study evaluated the association of a polymorphism in the CD40 gene with BMD and risk of osteopenia or osteoporosis in a population of 602 postmenopausal women. Results showed that women with the TT genotype had lower BMD at femoral neck and spine sites and increased risk of osteopenia or osteoporosis. INTRODUCTION: Recent findings have demonstrated that the CD40/CD40L system, which is of main importance for the immune system, can also be implied in the regulation of bone metabolism. The main objective of the present work has been to clarify whether single nucleotide polymorphisms (SNPs) affecting genes of CD40/CD40L system could be linked with abnormalities in the level of bone mineral density (BMD) in menopausal women. METHODS: We performed an association study of BMD values with a SNP located at position -1 of the Kozak consensus sequence of CD40 gene (rs1883832; C>T) in a population of 602 postmenopausal women. RESULTS: Women with the TT genotype (8.6% of women) displayed a reduction in femoral neck BMD (FN BMD) and lumbar spine BMD (LS BMD) of 6.2% and of 6.3%, respectively, as compared to women with CC + CT genotype. Logistic regression analysis adjusted for age, weight, and height showed that women with the TT genotype had increased risk for FN (odds ratio: 2.34; 95% CI: 1.12-4.89) and LS (odds ratio: 2.49; 95% CI: 1.19-5.24) osteopenia or osteoporosis. CONCLUSIONS: Women with the TT genotype in rs1883832 SNP affecting to Kozak consensus sequence of CD40 gene had lower BMD at FN and at LS sites and increased risk of osteopenia or osteoporosis.

Visualization of coherent destruction of tunneling in an optical double well system.

We report on a direct visualization of coherent destruction of tunneling (CDT) of light waves in a double well system which provides an optical analog of quantum CDT as originally proposed by Grossmann, Dittrich, Jung, and Hänggi [Phys. Rev. Lett. 67, 516 (1991)10.1103/PhysRevLett.67.516]. The driven double well, realized by two periodically curved waveguides in an Er:Yb-doped glass, is designed so that spatial light propagation exactly mimics the coherent space-time dynamics of matter waves in a driven double well potential governed by the Schrödinger equation. The fluorescence of Er ions is exploited to image the spatial evolution of light in the two wells, clearly demonstrating suppression of light tunneling for special ratios between the frequency and amplitude of the driving field.

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.