The negative-tone epoxy photoresist, SU-8, expands approximate to 1% by volume after postexposure baking. However, if the maximum optical fluence is comparable to that at the insolubility threshold, as in a holographic exposure, the developed resist shrinks (approximate to 35% by volume) due to the removal of light oligomers not incorporated into the polymeric network. IR spectroscopy shows that, at this level of exposure, only 15% of the epoxy groups in the insoluble polymer have reacted; consequently microstructural elements soften and collapse at > 100 degrees C. When the light oligomers are removed, the sensitivity of the resist is unchanged, provided that 5% (w/w) of a high-molecular-weight reactive plasticizer (glycidoxy-terminated polyethylene glycol) is added, but it shrinks less on development and, when used as a photonic crystal template, shows improved uniformity with less cracking and buckling. Reinforcing the polymer network by reaction with the polyfunctional amine (bis-N,N'-(3-aminopropyl) ethylenediamine) increases the extent of cross-linking and the thermal stability, allowing inverse replicas of photonic crystal templates to be fabricated from both Al:ZnO and Zr(3)N(4) using atomic layer deposition at temperatures up to 200 degrees C.

We report the replication of holographically defined photonic crystals using multistage atomic layer deposition. Low- and high-temperature atomic layer depositions were combined with selective etching to deposit and remove multiple conformal thin films within three-dimensional polymer templates. Using intermediate Al(2)O(3) inverse replicas, temperature-sensitive SU-8 photonic crystal templates were faithfully replicated with TiO(2) and GaP, greatly increasing the dielectric contrasts of the photonic crystals. Optical measurements are in good agreement with the calculated band structures.

We have registered the position and wavelength of a single InGaAs quantum dot using an innovative cryogenic laser lithography technique. This approach provides accurate marking of the location of self-organized dots and is particularly important for realizing any solid-state cavity quantum electrodynamics scheme where the overlap of the spectral and spatial characteristics of an emitter and a cavity is essential. We demonstrate progress in two key areas towards efficient single quantum dot photonic device implementation. Firstly, we show the registration and reacquisition of a single quantum dot with 50 and 150 nm accuracy, respectively. Secondly, we present data on the successful fabrication of a photonic crystal L3 cavity following the registration process.

We have shown that photolithography can be used to create alignment markers on a semiconductor substrate at cryogenic temperatures. The epoxy resist SU-8 can be exposed effectively by two-photon absorption at a temperature of 4K. By this means a spectroscopy apparatus can be used to find the positions of randomly distributed structures at low temperatures, such as InGaAs∕GaAs quantum dots, and mark their positions. We present a systematic study of the optical exposure parameters for cryogenic two-photon laser photolithography with SU-8.

Practical methods of microfabrication are vital for the development of photonic-crystal-based signal processing. However, extension of the optical methods that dominate integrated circuit fabrication to three dimensions is challenging. This communication reports an essential step for creation of devices operating within a full photonic band gap: atomic layer deposition is used to create the high-index TiO2 replicas of holographically defined photonic crystals shown in the figure.

Photonic-crystal devices must be precisely aligned within a photonic- crystal lattice. Rapid and flexible optical fabrication of a device embedded in, and in registration with, a 3D photonic crystal is demonstrated. Holographic lithography (see figure) is used to define the underlying periodic microstructure in a single exposure, and two-photon laser writing to create localized structural defects. An intermediate latent image of the photonic crystal is used to align the two exposures.

We have registered the position of single InGaAs quantum dots using a novel cryogenic laser photolithography technique. This would be useful in realizing solid state cavity quantum electrodynamics. By fabricating metal alignment markers around the quantum dot, it was registered with an accuracy of 50 nm. Following the marker fabrication process we demonstrated that the same quantum dot was reacquired, with an accuracy of 150 nm. The photoluminescence spectra from the quantum dots before and after processing were identical except for a small red shift (~1 nm), probably introduced during the reactive ion etching.

Holographic lithography is well-adapted to the production of three-dimensional photonic crystals for applications in the technologically important optical regime. We illustrate the flexibility of this approach by considering the design and fabrication of photonic crystals with symmetries that favour the formation of a complete photonic band gap. One of them, a structure with diamond symmetry, is calculated to have a complete gap at a refractive index contrast equal to the lowest yet reported.

We demonstrate the use of holographic lithography to fabricate chiral photonic crystals. These structures are calculated to exhibit strong optical activity even though they are made from material that is not intrinsically optically active. By control of the polarizations of the interfering plane waves that are used to define the three-dimensional microstructure it is possible to create left- and right-handed and closely related non-chiral structures.

We explore the analytical design of high-symmetry photonic crystals made by holographic lithography. We show how holographic lithography may be used to produce diamond-like photonic crystals that have a full, three-dimensional photonic band gap at a refractive index contrast equal to the lowest yet published.

We demonstrate that silica-acrylate materials doped with transition metal (Zr, Ti) oxide nanoparticles are suitable for the three-dimensional holographic lithography of photonic crystals with submicron periodicity and large inorganic contents. By careful choice of inorganic components, such composites could provide a route to the template-free, direct lithography of three-dimensionally ordered structures with high refractive-index contrast, submicron periodicity, and band gaps in the visible and infrared regions.

We describe a general and flexible technique for the fabrication of three-dimensional photonic crystals that is particularly well adapted to the production of structures with the sub-micron periodicity required for applications in the visible optical spectrum. Three-dimensional microstructure is generated by using a four-beam laser interference pattern to expose a thick layer of photoresist. Exposed areas are rendered insoluble; unexposed areas are dissolved away leaving a three-dimensional photonic crystal formed of cross-linked polymer with air-filled voids. The polymeric structure may be used as a template for the production of photonic crystals with higher refractive index contrast. Photonic crystals made of polymer and of TiO2 have been characterized by scanning electron microscopy and by optical diffraction measurements.

We have obtained hyperfine-resolved infrared spectra of a (P)Q(23)(N) branch line in the u =2-1 band of the X (3)Sigma(-) state of the molecular dication (DCl2+)-Cl-35. Analysis of the hyperfine structure allows us to estimate the magnitude of the Fermi contact interaction for the chlorine nucleus; b(F)(Cl) = 167 (25) MHz.

We have observed an infrared spectrum within the X 3Σ− state of DCl2+ using a fast-ion-beam/laser-beam spectrometer. A preliminary analysis shows good agreement with the rotational constants and tunneling lifetimes calculated by Bennett and McNab for the ν=1–2 vibrational band, although the calculated band origin appear to be in error by 21.1 cm−1.