PURPOSE: To obtain an optical head device which can magnify a beam spot diameter of an optical beam in matching with the size of a recording mark.
CONSTITUTION: A light collection device 10 includes a crystal member 20 including 1st and 2nd crystal regions 24, 26 whose crystal characteristic is revised. The 1st and 2nd crystal regions 24, 26 are formed between transparent electrodes 16 and 18. When a desired voltage is applied between the transparent electrodes 16 and 18, a desired phase difference is generated between the light beam passing through the 1st crystal region 24 and the laser beam passing through the second crystal region 26 and the beam spot diameter and the luminous intensity of the light beam passing through the two regions 24, 26 are changed to desired values. In this case, the 1st crystal region 24 is selected larger than the 2nd crystal region 26, then the beam spot diameter is magnified more than that of the incident optical beam.
MAEDA MASAKI
KOSHIYOUJI TAKASHI
