PROBLEM TO BE SOLVED: To correct for light intensity measurement errors due to color aberration.;SOLUTION: A variable wavelength monochromatic light source uses a beam splitter to split a light beam into two light beams, one light beam of which is irradiated on an irradiation surface via an output lens system and an output slit to produce output light and the other light beam is guided to a sensor to monitor intensity of the output light. The light source uses a dioptric system comprising a lens optical system which causes color aberration that leads to a situation where adjusting the system to produce an image properly on a projection surface at one wavelength results in a blurred and expanded image at another wavelength, spread of the output light at a slit opening varies and causes vignetting at the slit opening, and the relation between intensity of the incident light to the sensor and that of the light on the projection surface is altered, which prevents accurate measurement of the output light at the irradiation surface. In order to solve the problem, a sensor lens system and a sensor slit are provided between the beam splitter and the sensor, where specifications of components constituting both the sensor lens system and the sensor slit and the positional arrangement are identical to those of the output lens system and the output slit.;COPYRIGHT: (C)2013,JPO&INPIT
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