Ranjit, picking up the infrared band (?) might be the best way to go.
Especial if you are interested in suden variations in temperture on and object or distant flame. Intimate contact is really messy.

The way you do it is with an infrared phototransistor. When I was experimenting, I had the neadle of an ammeter deflecting noticable when I lit a lighter up to a meter or meter and a half. You might be able to get 10 meters with more amplification.