Hello,

i am Akshay, new to zemax. I designed a spectrometer with mirror transmission grating and lens system. i could not able to focus the beam spot within airy disk diffraction limit. 

i did optimisation added variables in the merit function editor , given weights changed them accordingly. i have seen some difference but not able to get it within the diffraction limit.

 source as single mode fiber as point source with entrance pupil dia , 0.0042 mm

wavelengths 815,840(central wavelength),860

object distance 0.022 mm calculated for 1/e2 intensity NA at 0.09

parabolic mirror MPD139-M01 - thorlabs

focussing lens AC254 150B - thorlabs

i attached the file here. 

i tried many things but cant figure it out myself , can anyone help me out , i will be grateful 

Thanks indeed

Cheers

Akshay