Optical monochromators having time dispersion correction

An optical filter for generating a filter output signal from a filter input signal, said filter output signal consisting of light from said filter input signal in a predetermined bandwidth at a center wavelength, said filter comprising:

• a first dispersive element;
• a second dispersive element;
• a first optical assembly;
• and
• a first signal path over which a portion of said filter input signal traverses and is diffracted from said first dispersive element to form a first intermediate beamthat is input to said first optical assembly which generates a second intermediate beam therefrom, said second intermediate beam being directed to said second dispersive element and being diffracted by said second dispersive element, a portion of said diffracted second intermediate beam forming a portion of said filter output signal,
• wherein said first intermediate beam is dispersed in time relative to said filter input signal and said second intermediate beam is dispersed in time relative to said input signal, however, said filter output signal has less time dispersion relative to said filter input signal than said first intermediate beam has relative to said filter input signal.