Place lime juice, sugar, vodka, raspberries and lime slices into a pestle and crush until the sugar is dissolved, about 1 minute. Add the mint leaves and bruise; just enough so they release their flavor. Let all the flavors blend for 1 -2 minutes.
Divide the raspberry mixture into two glasses, add ice and top each with about 1/4 cup chilled soda water.
Garnish with more mint leaves and raspberries, if desired. Serve immediately.
If you don't have a mortar and pestle, place mint leaves in a small bowl and crush with the back of a spoon.