Summary form only given. We report the generation of tuneable THz radiation (0.75-3 THz) through second order nonlinear effects in the excitation of excitons in GaAs/AlAs multi-quantum wells (MQWs), using readily available continuous wave (CW) laser diodes at room temperature. A MQW GaAs/AlAs sample was designed to have excitonic resonances at a wavelength accessible by commercially available lasers (850nm, 260mW), and have ElHHl-ElLHl splitting of 9.1meV. The sample was grown by MBE with the MQW region containing 30 repeats of 11.9nm GaAs separated by 7.1nm AlAs barriers. These preliminary measurements removed the substrate and cap layer. The sample was then capillary bonded to a diamond heat spreader [1]. Two collimated lasers were used to excite the excitonic resonances. Both lasers were normally incident to the sample surface. Figure 1(a) shows THz power obtained in collinear and crossed polarisations of the lasers with one laser resonant with the HH exciton, and the other laser tuned across the excitonic bands with both lasers operating at 260mW. A clear signal is observed in the case of collinear excitation which scales with the density of states of the excitons. Power dependence measurements confirm this is a second order non-linear effect. Using a simple interferometer, and fitting the measured power with the expected transmission of a Fabry-Perot etalon, frequency measurements indicate the ability to tune the THz radiation from 0.75-3THz. See Figs 1(b-d). For excitation at the peaks of HH and LH, a conversion efficiency of 1.2×10 -5 was obtained. This was achieved without the use of plasmonic effects, nor any kind of an antenna, nor an applied E-field to the structure. This offers the opportunity for the creation of compact, low cost, tuneable room temperature THz source.

This paper considers multiple structural designs for photonic crystal surface emitting lasers operating at key wavelengths. Initially a structure from Williams et al. is modelled, the structure is modified to include an additional GaAs waveguide layer (termed ballast layer) and to include an additional PC layer (termed double decker). These structures are modelled by a combination of coupling calculation and waveguide modelling and are compared to the original structure. We show that both of these schemes give an increase in coupling, but present fabrication challenges. Next, we model standard laser structures operating at key wavelengths (400 nm, 1.3 and 10 µm) where a photonic crystal is located above the active region and explore the effect of increasing thickness of photonic crystal. We find that increasing the thickness increases the coupling coefficient but not true for the full range of thicknesses considered. This study allows a more universal comparison of the use of all-semiconductor, or void containing PCSELs to be conducted and we find that the realisation of all semiconductor PCSELs covering a wide range of material and wavelengths are possible.

We report the generation of tuneable THz radiation (0.2-6 THz) and demonstrate a spectroscopic system operating at 750GHz. THz radiation is generated through second order nonlinear effects in the excitation of excitons in GaAs/AlAs multi-quantum wells (MQWs), using readily available continuous wave (CW) laser diodes at room temperature. An MBE grown 30×MQW GaAs(l 1.9nm)/AlAs(7.1nm) sample was designed to have excitonic resonances at a wavelength accessible by commercially available lasers (~850nm), and have E1HH1-E1LH1 splitting of 9.1meV. Two collimated, normally incident lasers were used to excite the excitonic resonances. Figure 1 (a) shows THz power obtained in collinear and crossed polarisations of the lasers with one laser resonant with the HH exciton, and the other laser tuned across the excitonic bands with each laser operating at 130mW output power. A clear signal is observed in the case of collinear excitation which scales with the density of states of the excitons. Power dependence measurements confirm this is a second order non-linear effect. Using a simple interferometer, and fitting the measured power with the expected transmission of a Fabry-Perot etalon, frequency measurements confirm the ability to tune the THz radiation from 0.75-3THz. See Figs 1(b-d). Tuning over the full range of Fig 1(a) indicates that THz generation os possible from -0.2 to 6THz. For excitation at the peaks of HH and LH, a conversion efficiency of 1.2×10 was obtained. This was achieved without the use of plasmonic effects, nor any kind of an antenna, nor an applied E-field to the structure. Spectroscopy using this new tuneable/sweepable light source will be presented at the conference. Future prospects for this technology will be discussed.

Electronic control of coherence in 2D arrays of photonic crystal surface emitting lasers is discussed.

Mode control in photonic crystal surface emitting lasers is demonstrated through the use of distributed, varying phase feedback introduced through cleaved facets.

We demonstrate a semiconductor PCSEL array that uniquely combines an in-plane waveguide structure with nano-scale patterned PCSEL elements. This novel geometry allows two-dimensional electronically controllable coherent coupling of remote vertically emitting lasers. Mutual coherence of the PCSEL elements is verified through the demonstration of a two-dimensional Young's Slits experiment. In addition to allowing the all-electronic control of the interference pattern, this type of device offers new routes to power and brightness scaling in semiconductor lasers, and opportunities for all-electronic beam steering.

The multiple quantum well (MQW) structure designed to utilize light hole (lh) and heavy hole (hh) energy states for producing coherent excitation of lh and hh excitons and resulting in radiation in the THz range of frequencies. Energies of states can be tunable with applied electric bias, resulting in a tunability of the radiation frequency. In our work, we aim to produce room temperature tunable THz radiation by optically exciting the QB sample using continues wave (CW) laser sources. In order to maximize the incident power upon the sample, and simplify the collection of the THz radiation, a structure, which has had the substrate, removed by using different method as thinning and wet etching, and capillary bonded to diamond is required.

We investigated the beam divergence in far-field region, diffraction loss and optical confinement factors of semiconductor photonic crystal surface emitting lasers containing either InGaP/GaAs or InGaP/air photonic crystals. The maximum in-plane feedback in PCSELs with InGaP/GaAs PCs has been observed at the ratio between PC atom radius and the lattice constant of 0.2 and 0.38. The surface emission grows as the size of atom increases.

Photonic crystal surface emitting lasers (PCSELs) [1] offer the ultimate in control in semiconductor lasers. PCSELs have been shown to have high power scaling with area, high single-mode powers [2], large scale coherent emission, control of the beam shape and polarization with design of the photonic crystal geometry [3,4], as well as beam steering [5]. The photonic crystal, a two-dimensional variation in refractive index, provides feedback in multiple orthogonal directions. Wave propagating in various directions couple with one another and a 2D standing wave (cavity mode) is constructed over a broad area. These devices have previously been fabricated through wafer fusion or the formation of voids during the re-growth process. The manufacturability of such devices prompted the move towards epitaxially regrown structures that do not contain voids.