Load material

.x MgF2.C

or 

.x fusedSilica.C

Load photocathode

.x QE58.C

Load Cherenkov simulation

.L photonMap3D.C

Create histogram

TH3D *name = new TH3D("Title 1","Title 2",bins etc.)

Run Cherenkov simulation

photonMap3D(histogram, Double_t dx (<100), Int_t nx (50?), Double_t dlam (.01<), 
			Int_t nlam (800), Double_t lam0 (.1), Double_t xstart (0),
			Double_t ystart (0), Double_t phi (0), Double_t alpha (0))

Look at data

Project3D, Draw

Make hspice current file

.L pads2spice.C

pads2spice(histogram,"filename",gain (10e6))