Hi welcome to Health care magic forum, The laser treatment
some times cause purple patches on the skin upto some time and slowly go away. If it is long since you had laser treatment it could be some allergy
on that hand may be due to some allergen on that hand like watch strap, bangle or some thing of that sort.
I advise you to consult a physician for diagnosis and treatment, He will try to find out the allergen and advise you to avoid some such things which are allergic to you. Besides i advise you to follow some diet recommendations as avoid taking fish, other sea foods, and brinjal .
Wishing for a quick recovery and thanks for calling.