Has someone tried to keep a CD at a further distance from the CD-pickup-reader?
http://www.farnell.com/datasheets/1944121.pdf 
Should tell you most of what you want to know. The lens focus is 3.6mm so that would be where the CD or your sensor needs to sit for the beam to be focused. Removing the lens will cause the beam to spread out over a large area as opposed to focusing on a spot so i'm not sure what you would achieve in doing that. In terms of the 'range of IR light' the data sheet says 760-800nm wavelength so no measuring needed :)