>> TGS_phase_analysis('V_single_crystal-2019-06-30-06.40um-70degrees#2-POS-1.txt','V_single_crystal-2019-06-30-06.40um-70degrees#2-NEG-1.txt',6.4,1)

f2 = 

     General model:
     f2(x) = A.*(erfc(q*sqrt(k*(x+start_time)))-beta*exp(-q^2*k*(x+start_time)
                    )./sqrt((x+start_time)))+B.*sin(2*pi*(peak_freq)*(x+
                    start_time)+p)*exp(-(x+start_time)/t)+D
     Coefficients (with 95% confidence bounds):
       A =     0.05304  (0.05218, 0.05391)
       k =   1.099e-05  (1.076e-05, 1.122e-05)
       beta =   1.697e-08  (-9.736e-07, 1.008e-06)
       B =     0.01247  (0.0123, 0.01263)
       p =       2.327  (2.317, 2.336)
       t =    4.29e-08  (4.207e-08, 4.373e-08)
       D =    0.000648  (0.0004977, 0.0007983)
     Problem parameters:
       q =   9.817e+05
       start_time =     1.4e-09
       peak_freq =   3.952e+08

ans =

   3.9522e+08