A method of generating laser pulses (1) includes: creating a circulating light field in resonator device (11) having resonator length L and an intra-cavity dispersion and configured for supporting light field resonator modes, and generating a pulse train of laser pulses (1) by a mode-locking mechanism. Laser pulses (1) are generated with a repetition frequency and provide a frequency comb with carrier frequency ωo and comb modes in frequency space. The intra-cavity dispersion is selected such that round trip phases ϕ have a dependency on frequency ω according to ϕ ⁡ ( ω ) = π ⁢ ⁢ m ⁡ ( 1 + 4 ⁢ ⁢ ω - ω 0 m ⁢ ⁢ ω r - 1 ) + L c ⁢ ω 0 wherein m is an integer providing effective repetition rate (mωr) in combination with mode spacing ωr at optical carrier frequency (ωo), and the mode-locking mechanism provides a coupling of the resonator modes whereby frequency difference (Δn=ωn+1−ωn) between neighboring mode frequencies (ωn, ωn+1) is a linear function of mode frequency number n. Furthermore, a spectroscopy method for investigating a sample, a laser pulse source apparatus and a spectroscopy apparatus are described.