Q-switch of a continuously pumped CO2 laser with a scanning coupled-cavity Michelson mirror

International audienceWe report on the possibility of Q-switching a continuously pumped CO2 laser using a scanning Michelson interferometer as an end mirror, instead of the habitual well-known strategies. This method, in addition to its simplicity, produces free tail relaxation pulses having duration of about 1.3 µs, which is comparable to what can be obtained when using a saturable absorber. A pulse repetition frequency as high as 90 kHz is obtained

Modelling of a Nd:YAG laser Q-switched by a scanning interferometric mirror

International audienceWe have modelled a continuously pumped Nd:YAG actively Q-switched by a variable interferometric mirror made up of a scanning Michelson or Fabry–Pérot mirror. We have characterised the three-mirror laser dynamics by using a bifurcation diagram constructed from the plot of peak power-enhancement factor as a function of mirror speed. One observes different chaotic windows separated by period-doubling bifurcations, and stable periodic regime. It is demonstrated that the best performance of the Q-switched laser is obtained rather for low than for high mirror speed (pulse width of 20 ns, and high peak power up to 400 times greater than the continuous emission)

Modelling of a Nd:YAG laser Q-switched by a scanning interferometric mirror

International audienceWe have modelled a continuously pumped Nd:YAG actively Q-switched by a variable interferometric mirror made up of a scanning Michelson or Fabry–Pérot mirror. We have characterised the three-mirror laser dynamics by using a bifurcation diagram constructed from the plot of peak power-enhancement factor as a function of mirror speed. One observes different chaotic windows separated by period-doubling bifurcations, and stable periodic regime. It is demonstrated that the best performance of the Q-switched laser is obtained rather for low than for high mirror speed (pulse width of 20 ns, and high peak power up to 400 times greater than the continuous emission)

Diffraction-limited microfocusing generated by polymer microlines separated by 1.12 μm

International audienceThe diffraction of a dielectric microline pair is optimized by numerical simulations to generate an efficient focus-ing pattern with a micron-scale footprint. Microlines separated by 1.12 μm are fabricated by two-photon polym-erization on a glass substrate, and their diffraction pattern is characterized by three-dimensional wide-field transmission microscopy. A line pair, having a width W ¼ 0.40 μm and a height H ¼ 0.80 μm, leads to diffraction-limited focusing in the visible spectrum. Depending on wavelength, its focal length, lateral resolution, and depth of focus are in the ranges of 0.8-1.3 μm, 0.22-0.44 μm, and 1.7-2.13 μm, respectively. Such a microlens based on the diffraction of only two subwavelength scatterers could be used for the design of miniature optical sensors with micron and sub-micron pixels

Quadratic phase modulation and diffraction-limited microfocusing generated by pairs of subwavelength dielectric scatterers

International audienceDiffractive approaches are needed when refrac-tive microlenses reach their focusing limit at the micron-scale in visible light. Previously, we have reported on micron-sized optical lenses based on the diffraction of metallic nanowires. Here, we extend our study to lenses based on pairs of subwavelength dielectric scatterers. Using simulations by two-dimensional finite element method, we demonstrate that focusing holds for pair spacings as small as the wavelength-size. For pairs with distances between inner walls larger than about 1.2λ, the scattered waves generate a quadratic phase modulation on the total propagating field leading to a diffrac-tion-limited focusing i.e. an effective optical lens effect with high numerical aperture. In addition, they have low sidelobe intensities, long depths of focus, and they have a low sensitivity with polarization. For pairs with inner wall distances smaller than about 1.2λ, the focus-ing phase modulation is accumulated during the propagation through the dielectric pair structure. In this work, we report only on the experimental demonstration for the case of larger wall separation to emphasize on the scattered wave effect on micro-focusing. A pair of parallel polymer lines (cylindrical lens), and a grid of polymer lines (square microlens array) with 2 μm-spacing were fabricated by two-photon induced polymerization. Their focal lengths are comparable to their separating distances, their spot-sizes are 0.37 μm and 0.28 μm at wavelength 530 nm, and their focusing efficiencies are 70% and 60%, respectively

Quadratic phase modulation and diffraction-limited microfocusing generated by pairs of subwavelength dielectric scatterers

Diffractive approaches are needed when refractive microlenses reach their focusing limit at the micron-scale in visible light. Previously, we have reported on micron-sized optical lenses based on the diffraction of metallic nanowires. Here, we extend our study to lenses based on pairs of subwavelength dielectric scatterers. Using simulations by two-dimensional finite element method, we demonstrate that focusing holds for pair spacings as small as the wavelength-size. For pairs with distances between inner walls larger than about 1.2λ, the scattered waves generate a quadratic phase modulation on the total propagating field leading to a diffraction-limited focusing i.e. an effective optical lens effect with high numerical aperture. In addition, they have low sidelobe intensities, long depths of focus, and they have a low sensitivity with polarization. For pairs with inner wall distances smaller than about 1.2λ, the focusing phase modulation is accumulated during the propagation through the dielectric pair structure. In this work, we report only on the experimental demonstration for the case of larger wall separation to emphasize on the scattered wave effect on micro-focusing. A pair of parallel polymer lines (cylindrical lens), and a grid of polymer lines (square microlens array) with 2 μm-spacing were fabricated by two-photon induced polymerization. Their focal lengths are comparable to their separating distances, their spot-sizes are 0.37 μm and 0.28 μm at wavelength 530 nm, and their focusing efficiencies are 70% and 60%, respectively

Absorption spectrum and analysis of the ND4 Sch\ufcler band

A high-resolution absorption spectrum of the main Sch\ufcler band of ND4, with heads at 6746 and 6749 \uc5 (\u3bd00 = 14828 cm 121), has been obtained by the flash discharge method, using mixtures of ND3 and D2. The spectrum confirms and extends the recent observation of ND4 absorption in laser frequency modulation spectroscopy by Hunziker and co-workers. The detailed rotational analysis establishes the electronic assignment as 3p2F2 \u2190 3s2A1, and results in molecular constants in moderate agreement with expectations based on ab initio calculations. The 30-\u3bcsec lifetime of the 3s2A1 ground state of ND4 is consistent with the 20-\u3bcsec lower limit estimated by Porter and co-workers on the basis of neutralized-ion-beam spectroscopy.Peer reviewed: YesNRC publication: Ye