Self-referencing a continuous-wave laser with electro-optic modulation

We phase-coherently measure the frequency of continuous-wave (CW) laser light by use of optical-phase modulation and f-2f nonlinear interferometry. Periodic electro-optic modulation (EOM) transforms the CW laser into a continuous train of picosecond optical pulses. Subsequent nonlinear-fiber broadening of this EOM frequency comb produces a supercontinuum with 160 THz of bandwidth. A critical intermediate step is optical filtering of the EOM comb to reduce electronic-noise-induced decoherence of the supercontinuum. Applying f-2f self-referencing with the supercontinuum yields the carrier-envelope offset frequency of the EOM comb, which is precisely the difference of the CW laser frequency and an exact integer multiple of the EOM pulse repetition rate. Here we demonstrate absolute optical frequency metrology and synthesis applications of the self-referenced CW laser with <5E-14 fractional accuracy and stability.Comment: 8 pages, 4 figure

Evaluation of Dietary Phytogenics on Growth Performance, Carcass Characteristics, and Economics of Grow-finish Pigs Housed Under Commercial Conditions

A total of 1,260 pigs (PIC 327 × 1050, initially 48.7 lb) were used in a 125-d trial to determine the effect of two dietary essential oil mixtures on the growth performance, carcass characteristics, and economics of finishing pigs. Pigs were allotted by BW and randomly assigned to 1 of 5 dietary treatments. Pigs were fed six dietary phases. Treatment 1 was the control with no feed additives and 12% of CP in the Phase 6 diet. Treatment 2 was the same formulation as treatment 1 but contained an essential oil mixture 1 (EOM 1) containing caraway, garlic, thyme, and cinnamon fed all phases. Treatment 3 was the same formulation as treatment 1 with EOM 1 fed from Phases 3 to 6 and essential oil mixture 2 (EOM 2) containing oregano, citrus, and anise fed all phases (EOM 1+2). Treatment 4 contained EOM 1 fed in all 6 phases with 16% CP in Phase 6. Treatment 5 contained ractopamine HCl (9 g/ton) with 16% CP in the Phase 6 diet. Overall (d 0 to 125), pigs fed diets with EOM 1+2 had increased (P = 0.003) ADFI compared with pigs fed the control treatment. Pigs fed the diet with EOM 1 and 16% CP had increased (P = 0.032) ADFI in comparison with the pigs fed ractopamine HCl treatment. Pigs fed the ractopamine HCl treatment had improved (P = 0.028) F/G compared with pigs fed the treatment with the EOM 1 and 16% CP and the control treatment. For carcass traits, pigs fed the treatment with EOM 1+2 and had increased (P = 0.007) HCW compared with pigs fed EOM 1 and 12% CP and the control treatment (P = 0.002). Pigs fed the treatment with ractopamine HCl also had heavier (P = 0.001) HCW compared with the control treatment. Pigs fed diets with EOM 1+2 had increased (P = 0.001) carcass ADG, compared with pigs fed the control treatment and the treatment with EOM 1 and 12% CP (P = 0.019). Pigs fed the treatment with ractopamine HCl also had improved (P = 0.001) carcass ADG compared with pigs fed the control treatment. Pigs fed diets with EOM 1+2 had increased (P = 0.021) carcass yield compared with pigs fed the treatment with EOM 1 and 12% CP. Carcass yield was improved (P = 0.036) for the treatment with ractopamine HCl in comparison with the control treatment. Economically, feed cost per pound of gain was lower (P \u3c 0.001) for pigs fed the control treatment compared to the treatment with EOM 1+2 and pigs fed with the ractopamine HCl treatment. Pigs fed diets with EOM 1+2 or ractopamine HCl treatment had increased (P = 0.001) gain value compared with pigs fed the control treatment. Pigs fed the ractopamine HCl treatment had increased income over feed cost in comparison with the treatments containing EOM 1 with 16% CP. In conclusion, the addition of EOM 1+2 improved ADFI, HCW, carcass ADG, and gain value in comparison with the control treatment. However, the increase in gain was not sufficient to overcome the increase in feed cost. The gain value improvement for the regimen with ractopamine HCl compensated for the extra feed cost resulting in a higher income over feed cost compared with the treatment with EOM 1 and 16% CP

“Tying Incumbents’ Hands”: The Effects of Election Monitoring on Electoral Outcome

Electoral observation missions (EOM) are designed to promote improvements in democratic quality by overseeing elections, but how successful are they? We argue that EOM tie the hands of incumbents, who have to adjust their electoral misconduct strategies, thus opening up political competition and making it more likely that the opposition will do well. Moreover, we propose that monitoring effects are conditioned by regime type, expecting that EOM presence has a stronger impact on electoral competition in autocracies than in democracies. Using a dataset of 580 parliamentary and presidential elections in 108 countries between 1976 and 2009 we find support for our theoretical claims. EOM increase electoral competitiveness in dictatorships by reducing margins of victory for incumbents, but leave competition unaffected in democracies. Furthermore, our analysis indicates that, contrary to previous findings, EOM increase the probability of electoral turnover in dictatorships but have no effect on democracies

A direct proof of Malus' theorem using the symplectic structure of the set of oriented straight lines

We present a direct proof of Malus' theorem in geometrical Optics founded on the symplectic structure of the set of all oriented straight lines in an Euclidean affine space. Nous pr\'esentens une preuve directe du th\'eor\`eme de Malus de l'optique g\'eom\'etrique bas\'ee sur la structure symplectique de l'ensemble des droites orient\'ees d'un espace affine euclidien

Analysis/Reduction of Residual Amplitude Modulation in Phase/Frequency Modulation by an EOM

Summary form only given. Frequency modulation (FM) is a powerful tool for sensitive spectroscopy and laser frequency stabilization. The high potential modulation frequency and FM format makes it easier to achieve shot-noise limit detection. Usually the laser frequency is modulated by an external frequency modulator such as an electrooptic modulator (EOM). However to obtain a pure FM signal is not easy because of residual amplitude modulation (RAM) arising by several effects: 1) etalon effects by light scattering within and at surfaces of the EOM crystal; 2) piezo-electric response of the EOM crystal, leading to beam steering and/or spatial position dither; 3) spatial inhomogeneity of modulation field in EOM crystal, leading to angular deviation of the beam and/or impure FM when part of the beam is selected; 4) and temperature dependence of the RAM associated with changes of the EOM crystal\u27s optical path and birefringence. RAM can easily be in the percent domain, and degrades the sensitivity in the FM spectroscopy, and also gives undesirable frequency offsets from the frequency reference. To solve the RAM problem, we measured and analyzed the RAM experimentally. A new active RAM suppression system is suggested

Mechanical oscillations in lasing microspheres

We investigate the feasibility of activating coherent mechanical oscillations in lasing microspheres by modulating the laser emission at a mechanical eigenfrequency. To this aim, 1.5% Nd3+:Barium-Titanium-Silicate microspheres with diameters around 50 {\mu}m were used as high quality factor (Q>10^6) whispering gallery mode lasing cavities. We have implemented a pump-and-probe technique in which the pump laser used to excite the Nd3+ ions is focused on a single microsphere with a microscope objective and a probe laser excites a specific optical mode with the evanescent field of a tapered fibre. The studied microspheres show monomode and multi-mode lasing action, which can be modulated in the best case up to 10 MHz. We have optically transduced thermally-activated mechanical eigenmodes appearing in the 50-70 MHz range, the frequency of which decreases with increasing the size of the microspheres. In a pump-and-probe configuration we observed modulation of the probe signal up to the maximum pump modulation frequency of our experimental setup, i.e., 20 MHz. This modulation decreases with frequency and is unrelated to lasing emission, pump scattering or thermal effects. We associate this effect to free-carrier-dispersion induced by multiphoton pump light absorption. On the other hand, we conclude that, in our current experimental conditions, it was not possible to resonantly excite the mechanical modes. Finally, we discuss on how to overcome these limitations by increasing the modulation frequency of the lasing emission and decreasing the frequency of the mechanical eigenmodes displaying a strong degree of optomechanical coupling.Comment: 17 pages, 5 figure