There are two types of therapeutic lasers, ablative lasers (also known as “hot” lasers, or high energy lasers), and non-ablative lasers (also known as “cold” lasers, or low level lasers).
Ablative lasers are used for acne, tattoo removal, skin resurfacing, hair removal and for surgery (e.g. for cutting skin or other tissue). High energy lasers are able to ablate (i.e. to excise, amputate, remove by erosion/melting/evaporation or otherwise destroy body tissue). In that sense, we can say that high energy levels work through “brute force”.
Ablative lasers are really good at treating superficial tissues by creating controlled damage, as in removing part of - or break down components of - the upper surface of the skin (epidermis) in order to remove acne, tattoos, wrinkles and other blemishes. However, cellulite is found in the deepest layer of the skin and thereby it simply cannot be removed by hot lasers without first burning away (ablating) the rest of the skin itself
Having said all that, there is a case where ablative lasers are successfully used to melt fat (but NOT cellulite): that of laser-assisted liposuction, also known as smart-lipo, mini-lipo or laser liposuction (the latter should not be confused with the gimmicky, non-surgical “laser lipo”, analysed below). For smartlipo, a cannula is inserted underneath the skin (and therefore UNDER the cellulite layer) and melts the deep subcutaneous fat, which is then aspirated (sucked) out of the body more easily.
Smart lipo, or mini lipo, is great for removal of limited amounts of fat (normal lipo is better for larger amounts of fat), but it is an invasive liposuction procedure which usually causes quite a lot of scar tissue / skin hardening / fibrosis, and in addition it does NOT remove cellulite (cellulite is an integral part of the skin and therefore can not be removed)