Fraxel laser resurfacing - how long should the time interval be btw treatments for optimal results?

I would recommend spacing treatments apart at least 4 weeks. If you have any specific concerns I would discuss them with your treating physician.

Thanks for your inquiry annaphana.  Fractional laser treatments, like Palomar 1540, are best done in a series of three to five treatments depending upon your skin condition and treatment goals.  The final results are cumulative as you are resurfacing anywhere from 15 to 30 percent of the skin with each treatment. Be aware that the greater the percentage of skin treated, the more "downtime" you will have.  
In my experience, doing the treatments in succession will produce better results.  Also if you do a series this year, you may only do one or two next year.  Repeating the treatments every year or two will keep your skin in great condition for many years.