Examples are disclosed that relate to efficiently producing multiple laser beams of a harmonic frequency from a fundamental frequency beam. One example provides a laser system comprising a laser configured to output a fundamental frequency beam, a first harmonic-generation stage, and a second harmonic-generation stage. The first harmonic-generation stage is configured to receive an input of the fundamental frequency beam from the laser, and output from the laser system a first-stage harmonic frequency beam and a first-stage residual fundamental frequency beam. The second harmonic-generation stage is configured to receive an input of the first-stage residual fundamental frequency beam, and to output from the laser system a second-stage harmonic frequency beam.

An alkali free glass has an average coefficient of thermal expansion at 50 to 350° C. of 30×10.sup.−7 to 43×10.sup.−7/° C., a Young's modulus of 88 GPa or more, a strain point of 650 to 725° C., a temperature T.sub.4 at which a viscosity reaches 10.sup.4 dPa.Math.s of 1,290° C. or lower, a glass surface devitrification temperature (T.sub.c) of T.sub.4+20° C. or lower, and a temperature T.sub.2 at which the viscosity reaches 10.sup.2 dPa.Math.s of 1,680° C. or lower. The alkali free glass contains, as represented by mol % based on oxides, 62 to 67% of SiO.sub.2, 12.5 to 16.5% of Al.sub.2O.sub.3, 0 to 3% of B.sub.2O.sub.3, 8 to 13% of MgO, 6 to 12% of CaO, 0.5 to 4% of SrO, and 0 to 0.5% of BaO. MgO+CaO+SrO+BaO is 18 to 22%, and MgO/CaO is 0.8 to 1.33.

An alkali free glass has an average coefficient of thermal expansion at 50 to 350° C. of 30×10.sup.−7 to 43×10.sup.−7/° C., a Young's modulus of 88 GPa or more, a strain point of 650 to 725° C., a temperature T.sub.4 at which a viscosity reaches 10.sup.4 dPa.Math.s of 1,290° C. or lower, a glass surface devitrification temperature (T.sub.c) of T.sub.4+20° C. or lower, and a temperature T.sub.2 at which the viscosity reaches 10.sup.2 dPa.Math.s of 1,680° C. or lower. The alkali free glass contains, as represented by mol % based on oxides, 62 to 67% of SiO.sub.2, 12.5 to 16.5% of Al.sub.2O.sub.3, 0 to 3% of B.sub.2O.sub.3, 8 to 13% of MgO, 6 to 12% of CaO, 0.5 to 4% of SrO, and 0 to 0.5% of BaO. MgO+CaO+SrO+BaO is 18 to 22%, and MgO/CaO is 0.8 to 1.33.

A glass has a density of 2.60 g/cm.sup.3 or lower, a Young's modulus of 88 GPa or more, a strain point of 650 to 720 C., a temperature T.sub.4 at which a glass viscosity reaches 10.sup.4 dPa.Math.s of 1,320 C. or lower, a glass surface devitrification temperature (T.sub.c) of T.sub.4+20 C. or lower, and an average coefficient of thermal expansion of 3010.sup.7 to 4310.sup.7/ C. at 50 to 350 C. The glass contains, as represented by mol % based on oxides, 50 to 80% of SiO.sub.2, 8 to 20% of Al.sub.2O.sub.3, 0 to 0.5% in total of at least one kind of alkali metal oxide selected from the group consisting of Li.sub.2O, Na.sub.2O and K.sub.2O, and 0 to 1% of P.sub.2O.sub.5.

An alkali free glass has an average coefficient of thermal expansion at 50 to 350 C. of 3010.sup.7 to 4310.sup.7/ C., a Young's modulus of 88 GPa or more, a strain point of 650 to 725 C., a temperature T.sub.4 at which a viscosity reaches 10.sup.4 dPa.Math.s of 1,290 C. or lower, a glass surface devitrification temperature (T.sub.c) of T.sub.4+20 C. or lower, and a temperature T.sub.2 at which the viscosity reaches 10.sup.2 dPa.Math.s of 1,680 C. or lower. The alkali free glass contains, as represented by mol % based on oxides, 62 to 67% of SiO.sub.2, 12.5 to 16.5% of Al.sub.2O.sub.3, 0 to 3% of B.sub.2O.sub.3, 8 to 13% of MgO, 6 to 12% of CaO, 0.5 to 4% of SrO, and 0 to 0.5% of BaO. MgO+CaO+SrO+BaO is 18 to 22%, and MgO/CaO is 0.8 to 1.33.

The same digital data is recorded with highly integrated manner on a plurality of media able to durably hold information over long-term. A minute graphic pattern indicating data bit information is drawn on a resist layer formed on a quartz glass substrate by exposing a beam and developed so as to prepare a master medium (M1), which comprises the quartz glass substrate having a minute recess and protrusion structure formed by etching where the remaining resist are used as a mask (FIG. (a)). The recess and protrusion structure recorded on the master medium (M1) is shaped and transferred onto a flexible recording medium (G2) on which a UV curable resin layer (61) is formed, whereby an intermediate medium (M2) is prepared (FIGS. (b)-(d)). The inverted recess and protrusion structure transferred to the intermediate medium (M2) is shaped and transferred onto a recording medium (G3) comprising a quartz glass substrate (70) on which a UV curable resin layer (80) is formed, whereby a reproduction medium (M3) having the same recess and protrusion structure as that of the master medium (M1) is prepared (FIGS. (e)-(h)). In shaping and transferring process, the media are separated using the flexibility of the intermediate medium (M2).

The same digital data is recorded with highly integrated manner on a plurality of media able to durably hold information over long-term. A minute graphic pattern indicating data bit information is drawn on a resist layer formed on a quartz glass substrate by exposing a beam and developed so as to prepare a master medium (M1), which comprises the quartz glass substrate having a minute recess and protrusion structure formed by etching where the remaining resist are used as a mask (FIG. (a)). The recess and protrusion structure recorded on the master medium (M1) is shaped and transferred onto a flexible recording medium (G2) on which a UV curable resin layer (61) is formed, whereby an intermediate medium (M2) is prepared (FIGS. (b)-(d)). The inverted recess and protrusion structure transferred to the intermediate medium (M2) is shaped and transferred onto a recording medium (G3) comprising a quartz glass substrate (70) on which a UV curable resin layer (80) is formed, whereby a reproduction medium (M3) having the same recess and protrusion structure as that of the master medium (M1) is prepared (FIGS. (e)-(h)). In shaping and transferring process, the media are separated using the flexibility of the intermediate medium (M2).

An alkali free glass has an average coefficient of thermal expansion at 50 to 350? C. of 30?10.sup.?7 to 43?10.sup.?7/? C., a Young's modulus of 88 GPa or more, a strain point of 650 to 725? C., a temperature T.sub.4 at which a viscosity reaches 10.sup.4 dPa.Math.s of 1,290? C. or lower, a glass surface devitrification temperature (T.sub.c) of T.sub.4+20? C. or lower, and a temperature T.sub.2 at which the viscosity reaches 10.sup.2 dPa.Math.s of 1,680? C. or lower. The alkali free glass contains, as represented by mol % based on oxides, 62 to 67% of SiO.sub.2, 12.5 to 16.5% of Al.sub.2O.sub.3, 0 to 3% of B.sub.2O.sub.3, 8 to 13% of MgO, 6 to 12% of CaO, 0.5 to 4% of SrO, and 0 to 0.5% of BaO. MgO+CaO+SrO+BaO is 18 to 22%, and MgO/CaO is 0.8 to 1.33.

A data storage medium includes a convexoconcave structure formed in a storage area which is set on a first surface of a quartz glass substrate. The storage area includes a plurality of unit storage areas which are arrayed at least in one direction, and non-data storage areas which are disposed between the unit storage areas, which are adjacent to each other. The convexoconcave structure includes unit data patterns, address patterns and boundary patterns. The unit data patterns are formed in the plurality of unit storage areas respectively in the array sequence of the unit storage areas, and the address patterns are formed in the non-data storage areas so as to correspond to each of the unit storage areas in which the unit data patterns are formed respectively.

A data storage medium includes a convexoconcave structure formed in a storage area which is set on a first surface of a quartz glass substrate. The storage area includes a plurality of unit storage areas which are arrayed at least in one direction, and non-data storage areas which are disposed between the unit storage areas, which are adjacent to each other. The convexoconcave structure includes unit data patterns, address patterns and boundary patterns. The unit data patterns are formed in the plurality of unit storage areas respectively in the array sequence of the unit storage areas, and the address patterns are formed in the non-data storage areas so as to correspond to each of the unit storage areas in which the unit data patterns are formed respectively.