Multiple-pass monochromators

Multiple-pass double-dispersion accessory optics are now available for the 0.67 to 2 m focal length monochromators from McPherson. McPherson multiple-pass monochromators allow you to work with low f/number, great throughput and twice the resolution. Unique `doubling' of resolution and dispersion is achieved by plane folding mirrors that multiply the monochromator focal length. Inside the instrument the fold mirrors repeat the light path. The monochromator aperture ratio (f/number) is unchanged. Light passes over the diffraction grating two times. The multiple-pass monochromator is useful for reaching twice the resolution or dispersion with very aggressive f/number and excellent light throughput. Scanning monochromator applications as well as imaging and other CCD-based detection approaches benefit.

McPherson multiple-pass monochrom­ators are ideal for experiments where more spectral resolution is required and laboratory space or budget cannot accommodate a physically larger instrument. The multiple-pass approach is not to be confused with double monochromators where light passes through two separate instruments to achieve low scatter light levels.

Figure 1 A McPherson multiple-pass monochromator.