PMC:2940544 / 5994-7421 JSONTXT

{"target":"https://pubannotation.org/docs/sourcedb/PMC/sourceid/2940544","sourcedb":"PMC","sourceid":"2940544","source_url":"https://www.ncbi.nlm.nih.gov/pmc/2940544","text":"Pulse splitting\nA few methods aimed at improving two-photon imaging utilize on alteration of the excitation beam itself. Of these, the technique of splitting ultrafast pulses in time by increasing repetition frequency (Ji et al., 2008) stands out and allows application of greater total laser power to the sample without oversaturation or photodamage. Pulse splitting utilizes a beam splitter with delaying mirrors to split each laser pulse into two smaller pulses. Each new pulse excites one quarter the fluorescence photons excited by the original pulse (the two-photon fluorescence process is proportional to square of excitation power), but there are twice as many of pulses, so without a change in the laser output power, this system creates half as much total excitation. On the other hand, by increasing the laser power, one can induce more total excitation and greater signal without crossing damage thresholds or saturating chromophores. This is true since one may double laser output to render each new pulse as powerful as the original pulse but there remain twice as many pulses (as long as the interpulse interval is sufficient to allow molecules of fluorophore to physically relax, this has not been a problem in practice, given that fluorescence lifetime of typical dyes is in 0.5–20 ns range). This approach of changing the properties of the laser beam itself may be combined with other methods discussed below.","divisions":[{"label":"title","span":{"begin":0,"end":15}}],"tracks":[{"project":"TEST0","denotations":[{"id":"20859526-109-117-568132","span":{"begin":230,"end":234},"obj":"[\"18204458\"]"}],"attributes":[{"subj":"20859526-109-117-568132","pred":"source","obj":"TEST0"}]},{"project":"0_colil","denotations":[{"id":"20859526-18204458-568132","span":{"begin":230,"end":234},"obj":"18204458"}],"attributes":[{"subj":"20859526-18204458-568132","pred":"source","obj":"0_colil"}]},{"project":"2_test","denotations":[{"id":"20859526-18204458-38464474","span":{"begin":230,"end":234},"obj":"18204458"}],"attributes":[{"subj":"20859526-18204458-38464474","pred":"source","obj":"2_test"}]}],"config":{"attribute types":[{"pred":"source","value type":"selection","values":[{"id":"TEST0","color":"#c893ec","default":true},{"id":"0_colil","color":"#93ecae"},{"id":"2_test","color":"#ec9493"}]}]}}