Large Photoinduced Refractive Index Changes Research Articles

Large Photoinduced Densification in Organically Modified Germanosilicate Glasses

Organically modified germanosilicate (ORMOGSIL) glasses prepared by a sol-gel method showed a large refractive index change on ultraviolet exposure. The large photoinduced refractive index change in the ORMOGSIL glasses is mainly due to the structural densification caused by ultraviolet irradiation. The shifts in frequency of the Raman bands measured at room temperature reveal structural densification by reduction of the average intertetrahedral bonding angle θ in the ORMOGSIL glasses. Surface relief patterns by photoinduced densification were directly inscribed on the ORMOGSIL glasses.

Large Photoinduced Refractive Index Change of Polymer Films Containing and Bearing Norbornadiene Groups and Its Application to Submicron-Scale Refractive-Index Patterning

We measured photoinduced refractive index changes of polymer films containing various norbornadiene compounds. Poly(methyl methacrylate) (PMMA) films containing 51.6 wt% of 5,6-(2-benzofuryl)-2,3-di(trifluoromethyl)-1,4,7,7-tetramethyl-2,5-norbornadiene (NBD4) showed refractive index changes of 0.037 during photoisomerization. A polymer film bearing thiophenyl- and benzofuryl- substituted norbornadiene groups (PolyTBFNBD) showed a refractive index change of 0.05–0.06 for 594–632.8 nm during photoisomerization. This value is the largest value of refractive index change so far in a nonresonant region induced by photochemical reactions. Submicron-scale patterning of pure refractive-index contrast on the PolyTBFNBD film was also demonstrated by using near-field scanning optical microscopy (NSOM).

Large Photoinduced Refractive Index Change in a Polyimide Film by Charge-Transfer Complex Formation with a Polymer-Bound Phenylazide Fragment

A large photo-induced refractive index change as large as 0.014 at 632.8 nm in thermostable transparent polymer films has been realized for the first time by using photoirradiation of polyimide precursor films containing a phenylazide and successive imidization. The phenylazide fragment forms a charge-transfer complex with imide moiety. The films maintained high transmittance in a wide visible region in contrast to usual polyimide films. This value of refractive index change is sufficient to make thermostable channel waveguides and other optical devices.

Large photoinduced refractive index changes in pulsed-laser-deposited lead germanate glass waveguides with controllable refractive index sign change

A study of the photosensitivity of lead germanate glasses grown by pulsed laser deposition is presented. Lead germanate films were grown from stoichiometric bulk targets, on borosilicate glass substrates in an oxygen atmosphere, to form optical waveguides. The films grown exhibited high absorption in the ultra violet spectral area (around 240 nm) which indicated the possibility of high photosensitivity. The photosensitivity of the materials was examined by phase mask and interferometric grating recording over a wide ultra violet spectral region (325nm-193nm) using various continuous and pulsed laser sources. Very high refractive index changes (up to 1%) have been observed along with variable sign of the refractive index change depending on the oxygen background pressure used during growth and recording intensity

Composition dependence of the photoinduced refractive-index change in lead silicate glasses

A large photoinduced refractive-index change (as great as Dn=0.21+/-0.04) is obtained in lead silicate glasses by irradiation with the frequency-quadrupled output of a Q -switched YAG laser (266 nm). An approximately exponential relationship is found between the photoinduced refractive-index change and the lead cation mole fraction over the composition range from 18.7% to 57%. The induced refractive-index change is permanent and shows no decay after heating to 360 degrees C during 1 h. Dispersion of the refractive-index change suggests that the photosensitivity is associated with changes in the intrinsic glass absorption edge.

Large photosensitivity in lead–silicate glasses

Strong, permanent surface-relief and refractive index gratings are written in lead–silicate glasses by irradiation with the output of a pulsed KrF excimer laser (248 nm) through a phase mask. Diffraction efficiencies as high as 10% are obtained. The diffraction efficiency of the refractive index grating after removal of the surface-relief grating shows that a very large photoinduced refractive index change (Δn0=0.09±0.02) is obtained.

Large Photoinduced Refractive Index Changes of Transparent Polymer Films Containing Photoeliminable Diazo and Azido Groups

We measured photoinduced refractive index changes of polymer films containing various compounds, such as α-diazoketone derivatives, azide derivatives, and others which induce the loss of nitrogen molecules during photoirradiation. PMMA films containing 20 wt % of 2-diazo-1-indanone (2DI) and β-azidostyrene (β-AS) showed large refractive index changes of 0.015 during photolysis, keeping transparency throughout the entire visible region. The fact that the chemical structure of the substituents at α-position of the diazo group and hence the resonance effect do not affect the photoinduced changes in refractive indices much indicates the major contribution of the elimination effect of nitrogen molecules to the refractive index changes. Azide derivatives except for β-AS showed small refractive index changes which may be related to the chemical structure of the photoproducts. Discussion is given on the estimation of the molar refraction and the contribution of the changes in electronic structure and in density t...

Photosensitivity of lead germanate glass waveguides grown by pulsed laser deposition

We report very large photoinduced refractive-index changes Dn, of the order of ~10(2), in lead germanate glass waveguides grown by pulsed-laser deposition. The magnitude of Dn was derived from measurements of diffraction efficiency for gratings written by exposure to 244-nm light through a phase mask, whereas the sign of Dn was determined from ellipsometric data. Results are shown for films grown under oxygen pressures ranging from 1 chi 10(-2) to 6 chi 10(-2)mbars (1.33mbars=1 Torr).

Large photoinduced refractive index changes of a polymer containing photochromic norbornadiene groups

We prepared a polymer containing pendant norbornadiene (NBD) moieties, P(MMA0.43-co-GMA0.57-PNCA), and measured absorbance and refractive index spectra before and after photoisomerization of norbornadiene moieties. Large photoinduced refractive index changes of ∼0.01 were obtained at 632.8 nm, the region far from the absorption band. A quantum yield of 0.50 was obtained for the photoisomerization of NBD moieties in this polymer. These values are sufficient to make efficient channel waveguides by photoisomerization.