A laser pulse sequence measuring method for measuring a delay between a pair of pulses from two laser pulse sequences (1, 2), comprises the steps of creating a first laser pulse sequence (1) of first laser pulses (1A) and a second laser pulse sequence (2) of second laser pulses (2A), and generating a delay signal (3) which represents the delay between the pair of pulses from the first and second laser pulse sequences (1, 2), wherein the step of generating the delay signal (3) includes creating intra-pulse difference frequency generation (IPDFG) pulses (4) by applying intra-pulse difference frequency generation to the first laser pulses (1A) in a difference frequency generation (DFG) medium (21), providing phase-stable reference waveforms (5) based on the IPDFG pulses (4), and electro-optic sampling (EOS) of the electric field of the phase-stable reference waveforms (5) with sampling pulses (6) in an EOS medium (22), wherein the sampling pulses (6) are created based on the second laser pulses (2A), for generating an electro-optic sampling (EOS) signal (7), wherein the delay signal (3) is obtained from the EOS signal (7). Furthermore, a spectroscopic measuring method, a laser pulse sequence measuring apparatus (100) and a spectroscopic measuring apparatus are described.