grating_mod grating_value[um] SAW_freq[Hz] SAW_freq_error[Hz] A[Wm^-2] A_err[Wm^-2] alpha[m^2s^-1] alpha_err[m2s-1] beta[s^0.5] beta_err[s^0.5] B[Wm^-2] B_err[Wm^-2] theta theta_err tau[s] tau_err[s] C[Wm^-2] C_err[Wm^-2]