FIG. 1 is a left side perspective view taken from the front and side of a diffuser, showing my new design;

FIG. 2 is a front view thereof;

FIG. 3 is a left side elevational view thereof;

FIG. 4 is a right side elevational view thereof;

FIG. 5 is a top plan view thereof;

FIG. 6 is a bottom plan view thereof; and,

FIG. 7 is a rear view thereof.

The broken line showing an electric vaporizer is for illustrative purposes only and forms no part of the claimed design.