| 摘要 |
PURPOSE:To reduce the variance in the focal length of a grating lens caused by temperature changes in the wavelength of a lighting source by utilizing positively the variance in the focus due to thermal expansion of the grating lens itself. CONSTITUTION:In using a laser diode 1 as a light source, the oscillated wavelength is prolonged with the rise of temperature and shortened with the decrease of temperature. It is known that the amount is 0.2-0.3nm/ deg.C. The focus (f) is inversely proportional to the wavelength lambda. That is, when temperature rises, the focus is shortened and when temperature falls down, the focus gets longer. In order to improve the said disadvantage, the thermal expansion of the grating lens itself is utilized. That is, each ring radius is increased by thermal expansion and the focus is prolonged. When the temperature decreases conversely, each zone is shrinked and the focus is shortened. In selecting properly the type of material of the grating lens 1, the variance in the focus length due to the said wavelength change is reduced. |
