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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