A simple and efficient optical interference method for fabricating high quality two- and three-dimensional (2D and 3D) periodic structures is demonstrated. Employing multi-exposure of two-beam interference technique, different types of periodic structures are created depending on the number of exposure and the rotation angle of the sample for each exposure. Square and hexagonal 2D structures are fabricated by a multi-exposure of two-beam interference pattern with a rotation angle of 90 masculine and 60 masculine between two different exposures, respectively. Three-exposure, in particular, results in different kinds of 3D structures, with close lattice constants in transverse and longitudinal directions, which is difficult to be obtained by the commonly used multi-beam interference technique. The experimental results obtained with SU-8 photoresist are well in agreement with the theoretical predictions. Multi-exposure of two-beam interference technique should be very useful for fabrication of photonic crystals.

We demonstrate a new 3D fabrication method to achieve the same results as those obtained by the two-photon excitation technique, by using a simple one-photon elaboration method in a very low absorption regime. Desirable 2D and 3D submicrometric structures, such as spiral, chiral, and woodpile architectures, with feature size as small as 190 nm have been fabricated, by using just a few milliwatts of a continuous-wave laser at 532 nm and a commercial SU8 photoresist. Different aspects of the direct laser writing based on ultralow one-photon absorption (LOPA) technique are investigated and compared with the TPA technique, showing several advantages, such as simplicity and low cost.

We investigate the electron spin resonance of an ensemble of Nitrogen-Vacancy (NV) color centers in a bulk diamond crystal. The four possible orientations of the NV-center in the lattice lead to different dependences on the magnitude and the orientation of an external static magnetic field. Experimental results obtained with a continuous microwave excitation are in good agreement with simulations. In addition, we observe that the average radiative lifetime of the NV color center is also modified when the external magnetic field is applied. This variation is explained by the mixing between mS = 0 and mS = ±1 spin states of the NV-center with different radiative lifetimes, due to magnetic coupling. These results are of interest for a broad range of applications, such as spin-resonance-based magnetometry with a high-density ensemble of NV-centers. PACS numbers: 72.25.Fe; 78.70.Gq; 42.50.Tx; 42.50.Dv; Due to its unique features, the Nitrogen-Vacancy (NV) color center in diamond is a promising system for numerous applications. At the individual level, the NVcenter is an efficient single-photon emitter. 1 Its electron spin properties with exceptional long coherence time 2,3 can be used to construct quantum gates operating at room temperature 4,5,6 and to measure magnetic field with nanoscale resolution. 7,8 At the high-density ensemble level, 9 NV-centers behave as very sensitive magnetometers on a micrometer scale 10,11 and are envisioned for building quantum memories where information is coherently in-and out-coupled to spin states. 12 Due to the C 3v symmetry of the NV-center in the diamond crystal, each defect has four possible orientations associated with the [111] axis of the crystal. 6 Here we discuss the influence of an external static magnetic field on the electron spin resonance of an ensemble of NVcenters. We also measure the magnetic field's influence on the average photoluminescence lifetime.Figure 1(a) shows the structure of an NV color center in a diamond lattice, fabricated in [110]-orientation. The NV-center consists of a substitutional nitrogen (N) associated to a neighboring vacancy (V). We start from a type-Ib HPHT single-crystal sample. NV-centers are then created from the initially embedded nitrogen impurities, by irradiation with a high-energy electron beam and annealing for 2 hours at 850 • C. With the applied irradiation dose of 10 13 electron/cm 2 , a density of about 200 NV-centers/µm 3 can be created. The energy levels of the NV-center are displayed in Fig. 1(b). The NV-center can be optically excited with a laser at a wavelength of 532 nm and emits a broadband luminescence with a zero phonon line at 637 nm. The emission spectrum is measured with an imaging spectrograph, and it shows that the diamond sample mostly contains negatively charged NV − centers. The ground state of the NV − center is known to have an electron spin triplet structure with a zero-field splitting of 2.87 GHz between the m S = 0 and the degenerate m S = ±1 states.Optical detection of the NV-center ensemble is realized ...

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We demonstrate a promising method to fabricate large-area periodic structures with desired defects by using the combination of multiple-exposure two-beam interference and mask-photolithography techniques. Multiple-exposure of two-beam interference pattern at 325 nm into a positive AZ-4620 (or a negative SU-8) photopolymerizable photoresist is used to form a square and hexagonal two-dimensional periodic structures. Desired defects are introduced in these structures by irradiating the sample with one beam of the same laser through a mask in which the design of defects is patterned. A 1cm x 1cm periodic structures with the lattice constant as small as 365nm embedding several kinds of defect, such as waveguide or Mach-Zehnder, was obtained by employing this combination technique. It shows that the proposed combination technique is useful for mass production of photonic crystal optoelectronics devices.

A new principle of lidar-radar is theoretically and experimentally investigated. The proposed architecture is based on the use of an rf modulation of the emitted light beam and a direct detection of the backscattered intensity. Use of a radar-processing chain allows one to obtain range and Doppler measurements with the advantages of lidar spatial resolution. We calculate the maximum range of this device, taking into account different possible improvements. In particular, we show that use of a pulsed two-frequency laser and a spatially multimode optical preamplification of the backscattered light leads to calculated ranges larger than 20 km, including the possibility of both range and Doppler measurements. The building blocks of this lidar-radar are tested experimentally: The radar processing of an rf-modulated backscattered cw laser beam is demonstrated at 532 nm, illustrating the Doppler and identification capabilities of the system. In addition, signal-to-noise ratio improvement by optical pre-amplification is demonstrated at 1.06 microm. Finally, a two-frequency passively Q-switched Nd:YAG laser is developed. This laser then permits two-frequency pulses with tunable pulse duration (from 18 to 240 ns) and beat frequency (from 0 to 2.65 GHz) to be obtained.

Diamond nanocrystals containing nitrogen-vacancy (NV) color centers have been used in recent years as fluorescent probes for near-field and cellular imaging. In this work, we report that an infrared (IR) pulsed excitation beam can quench the photoluminescence of a NV color center in a diamond nanocrystal (size <50 nm) with an extinction ratio as high as ≈90%. We attribute this effect to the heating of the nanocrystal consecutive to multiphoton absorption by the diamond matrix. This quenching is reversible: the photoluminescence intensity goes back to its original value when the IR laser beam is turned off, with a typical response time of 100 ps, allowing for fast control of NV color center photoluminescence. We used this effect to achieve the sub-diffraction-limited imaging of fluorescent diamond nanocrystals 4 These authors have contributed equally to this work. on a coverglass. For that, as in the ground state depletion super-resolution technique, we combined the green excitation laser beam with the control IR depleting one after shaping its intensity profile in a doughnut form, so that the emission comes only from the sub-wavelength size central part.

In this work, local thermal effect induced by a continuous-wave laser has been investigated and exploited to optimize the low one-photon absorption (LOPA) direct laser writing (DLW) technique for fabrication of polymer-based microstructures. It was demonstrated that the temperature of excited SU8 photoresist at the focusing area increases to above 100 °C due to high excitation intensity and becomes stable at that temperature thanks to the use of a continuous-wave laser at 532 nm-wavelength. This optically induced thermal effect immediately completes the crosslinking process at the photopolymerized region, allowing obtain desired structures without using the conventional post-exposure bake (PEB) step, which is usually realized after the exposure. Theoretical calculation of the temperature distribution induced by local optical excitation using finite element method confirmed the experimental results. LOPA-based DLW technique combined with optically induced thermal effect (local PEB) shows great advantages over the traditional PEB, such as simple, short fabrication time, high resolution. In particular, it allowed the overcoming of the accumulation effect inherently existed in optical lithography by one-photon absorption process, resulting in small and uniform structures with very short lattice constant.