Diode laser heterodyne Interferometer using direct modulation of wavelength

The wave front aberration tolerance for optical components should be of the order of one-fifteenth of a wavelength for precise optical systems such as optical disks or laser beam printers. Diode lasers are usually used as light soirees for these optical systems. Therefore, the need has been increasing for measurement of wave front aberrations using diode lasers1 rather than He-Ne lasers because of the high accuracy of the former resulting from exclusion of chromatic aberration. Moreover, a heterodyne interferometer has many advantages for such a measurement; not only does it assure high accuracy but also automatic electronic fringe analysis.2,3