A tissue treatment system comprising: a base unit having a power source and a reservoir for containing a cooling fluid , an applicator connected with the base unit via a cable , the applicator comprising: a tissue cooling element constructed and arranged to engage biological tissue for treatment, the tissue cooling element including channel structure there-through, a light source powered by the power source and constructed and arranged to generate light energy directed to the tissue cooling element and thus to the biological tissue , a first fluid passage disposed between the reservoir and the channel structure of the tissue cooling element and configured to deliver cooling fluid at a first temperature to the tissue cooling element to cool the biological tissue , such that the cooling fluid is heated to a second temperature upon heat exchange with the biological tissue , and a second fluid passage disposed between the channel structure and the reservoir and configured to return the cooling fluid to the reservoir , the second fluid passage being constructed and arranged to direct the cooling fluid , at the second temperature, to the light source to cool the light source prior to being returned to the reservoir , wherein the first and second fluid passages define a single cooling fluid circulation loop to cool both the tissue cooling element and the light source in series, and wherein a portion of each of the first and second fluid passages is disposed in the cable . a base unit having a power source and a reservoir for containing a cooling fluid , an applicator connected with the base unit via a cable , the applicator comprising: a tissue cooling element constructed and arranged to engage biological tissue for treatment, the tissue cooling element including channel structure there-through, a light source powered by the power source and constructed and arranged to generate light energy directed to the tissue cooling element and thus to the biological tissue , a tissue cooling element constructed and arranged to engage biological tissue for treatment, the tissue cooling element including channel structure there-through, a light source powered by the power source and constructed and arranged to generate light energy directed to the tissue cooling element and thus to the biological tissue , a first fluid passage disposed between the reservoir and the channel structure of the tissue cooling element and configured to deliver cooling fluid at a first temperature to the tissue cooling element to cool the biological tissue , such that the cooling fluid is heated to a second temperature upon heat exchange with the biological tissue , and a second fluid passage disposed between the channel structure and the reservoir and configured to return the cooling fluid to the reservoir , the second fluid passage being constructed and arranged to direct the cooling fluid , at the second temperature, to the light source to cool the light source prior to being returned to the reservoir , wherein the first and second fluid passages define a single cooling fluid circulation loop to cool both the tissue cooling element and the light source in series, and wherein a portion of each of the first and second fluid passages is disposed in the cable . <EOS>