1. A method of characterizing a sample, comprising: estimating a fluorescence impulse response (“h(n)”) of the sample, based upon an expansion including Laguerre coefficients (“{c j }”), the expansion being represented by the equation h ⁡ ( n ) = ∑ j = 0 L - 1 ⁢ c j ⁢ b j α ⁡ ( n ) ; and characterizing the sample by directly analyzing the Laguerre coefficients.