In a small saucepan, bring sugar and water to a boil, stirring until sugar is dissolved. Add 6 ounces raspberries; stirring occasionally, until softened, about 2-3 minutes. Remove from heat; let cool completely. Strain through fine-mesh sieve, pressing on solids with back of spoon; discard solids. Transfer syrup to glass jar or airtight container. Store in refrigerator until ready to use. Remaining syrup will keep up to one week.
Add the syrup to individual glass or pitcher. Squeeze a little fresh lime, fill with ice (preferably crushed), pour vodka, gently stir and finish off with sparkling water or lemon-lime soda.
Garnish with a few frozen raspberries and fresh thyme or mint.
*** To freeze raspberries; rinse and dry well. Place on plate or sheet pan in single layer. Transfer to freezer for a few hours or over night and voila!