Abstract: An optical fiber bundle for heat resistance and vacuum resistance which can be used even at a very high temperature or high vacuum is provided in economical manner. This is accomplished by a process for the production of an optical fiber bundle for heat resistance and vacuum resistance, which comprises making up optical fiber filaments each having a core part and a clad part into a bundle, closely fusion-bonding the end of the optical fiber bundle with a bonding glass and then subjecting the bonding glass to a crystallization treatment to increase the heat resistance.

Abstract: An infrared light-excited light-emitting substance given by the general formula:R1.sub.x R2(.sub.1-x)Ba.sub.z Cl.sub.3+2z where R1 is a rare-earth element, x satisfies the relation 0.01<x.ltoreq.1, R2 is another rare-earth element, and z satisfies the relation 1<z<4. Preferably, the substance is a transparent crystal having a transparency exceeding 70% in a wavelength range from 400 to 1500 nm, excluding wavelengths absorbed by rare-earth ions. The light-emitting substance can convert infrared light into visible light in a wavelength range from blue light to green light at a high conversion efficiency.

Abstract: A fluorophosphate optical glass having optical constants, i.e. a refractive index of 1.45 to 1.54 and an Abbe number of 75 to 90, preferably 75 to 89.5, useful as a lens for an optical instrument to obtain a good quality image, is provided, which has a chemical composition (% by mole) comprising:______________________________________ P.sub.2 O.sub.5 6.8-19.0% Al.sub.2 O.sub.3 1.5-6.0% BaO 0.3-6.6% AlF.sub.3 16.6-26.3% MgF.sub.2 2.5-19.0% CaF.sub.2 8.0-28.0% SrF.sub.2 9.7-35.0% BaF.sub.2 7.9-35.0% NaF 0.5-4.0% Gd.sub.2 O.sub.3 1.0-6.0% Y.sub.2 O.sub.3 0-3.5% La.sub.2 O.sub.3 0-3.5% Yb.sub.2 O.sub.3 0-3.5% sum of Gd.sub.2 O.sub.3, Y.sub.2 O.sub.3, La.sub.2 O.sub.3 and Yb.sub.2 O.sub.3 1.0-6.0% GdF.sub.3 0-2.0% CaO 0-3.5% SrO 0-3.5% ZnO 0-3.5% MgO 0-3.

Abstract: A fluorophosphate optical glass having optical constants, i.e. refractive index (nd) of 1.54 to 1.60 and Abbe number (.nu.d) of 68 to 75 and having abnormal partial dispersion represented by a relative partial dispersion of at least 0.537 is provided, which has a chemical composition (% by weight) comprising:______________________________________ Al(PO.sub.3).sub.3 15-32% Ba(PO.sub.3).sub.2 0-10% Sr(PO.sub.3).sub.2 0-10% Ca(PO.sub.3).sub.2 0-10% Mg(PO.sub.3).sub.2 0-10% sum of metaphosphates 20-32% BaF.sub.2 20-70% SrF.sub.2 5-40% CaF.sub.2 0-15% MgF.sub.2 0-10% AlF.sub.3 0-5% GdF.sub.3 0-5% sum of fluorides 55-75% Gd.sub.2 O.sub.3 5-22% La.sub.2 O.sub.3 0-7% Y.sub.2 O.sub.3 0-10% Yb.sub.2 O.sub.

Abstract: A fluorophosphate optical glass with a low refractive index and low dispersion is provided in stable manner, which has a refractive index nd of 1.42 to 1.47 and an Abbe number .nu.d of 90 to 97 and comprises 3 to 8 mole % of P.sub.2 O.sub.5, 0.1 to 2 mole % of Al.sub.2 O.sub.3, 1 to 7 mole % of BaO, 35.5 to 41 mole % of AlF.sub.3, 8 to 13 mole % of MgF.sub.2, 16 to 26 mole % of CaF.sub.2, 15 to 21 mole % of SrF.sub.2, 3.5 to 10 mole % of BaF.sub.2 and 1 to 6 mole % of NaF.