Volume hologram optical recording medium, composition for volume hologram recording layer formation, and volume hologram recording material

A composition for volume hologram recording layer formation for use in a volume hologram optical recording medium, comprising:

• a polymerizable photoactive compound (B) comprising a system capable of forming an optical image;
• a resin matrix (C) having a glass transition temperature of Tg of which is in the range of −45° C. or higher, wherein the resin matrix is a three dimensionally cross-linked resin;
• and
• at least one compound that is added to the system, and that is selected from the group consisting of a compound (A1) having a terpenoid structure, a compound (A2) represented by a formula (I):
• wherein R1 and R2 each represent an organic group having 1 to 20 carbon atoms, and R1 and R2 may combine to form a ring structure;
• and a cyclic or non-cyclic compound (A3) having at least two double bonds, two of these double bonds being present at 1 and 4 positions relatively, wherein upon volume hologram optical recording, the optical recording medium exhibits a ratio R1 of diffraction efficiency five minutes after a recording with a light irradiation of 10-10,000 pulses of 0.2-0.4 mW of recording light when the light irradiation is ceased to diffraction efficiency one minute after the recording when the light irradiation is ceased, wherein R1 is from 0.1 to 2.1.