A dual-comb spectrometer comprising: a first semiconductor laser source, serving as a local oscillator, operable to output a first light signal containing a first frequency comb consisting of a finite series of discrete frequencies separated by a first spacing defined as a first spectral range; a second semiconductor laser source, serving as an interrogator, operable to output a second light signal containing a second frequency comb consisting of a finite series of discrete frequencies separated by a second spacing defined as a second spectral range; and a sample detector operable to output a measurement signal and arranged to receive a combined light signal from superimposing the first and second light signals after at least the second light signal has traversed a sample space, the sample detector having a detection bandwidth that covers a frequency range corresponding to a third frequency comb that is detected by the sample detector as the measurement signal as a result of heterodyne mixing of the first and second light signals, the third frequency comb having a third spacing equal to the difference between the first and second spacings; characterised by: a controller configured to output first and second control signals to the first and second laser sources, the first and second control signals following first and second functional forms over each of one or more scan periods, wherein the first and second functional forms are defined as a coordinated pair to continuously or quasi-continuously tune the frequencies of the first and second frequency combs over a defined fraction of their free spectral ranges while keeping the frequency range of the third frequency comb within the bandwidth of the sample detector; and a data acquisition module arranged to collect a dataset of data points from the sample detector over each scan period, the or each dataset being collected while the first and second control signals are following the first and second functional forms. a first semiconductor laser source, serving as a local oscillator, operable to output a first light signal containing a first frequency comb consisting of a finite series of discrete frequencies separated by a first spacing defined as a first spectral range; a second semiconductor laser source, serving as an interrogator, operable to output a second light signal containing a second frequency comb consisting of a finite series of discrete frequencies separated by a second spacing defined as a second spectral range; and a sample detector operable to output a measurement signal and arranged to receive a combined light signal from superimposing the first and second light signals after at least the second light signal has traversed a sample space, the sample detector having a detection bandwidth that covers a frequency range corresponding to a third frequency comb that is detected by the sample detector as the measurement signal as a result of heterodyne mixing of the first and second light signals, the third frequency comb having a third spacing equal to the difference between the first and second spacings; characterised by: a controller configured to output first and second control signals to the first and second laser sources, the first and second control signals following first and second functional forms over each of one or more scan periods, wherein the first and second functional forms are defined as a coordinated pair to continuously or quasi-continuously tune the frequencies of the first and second frequency combs over a defined fraction of their free spectral ranges while keeping the frequency range of the third frequency comb within the bandwidth of the sample detector; and a data acquisition module arranged to collect a dataset of data points from the sample detector over each scan period, the or each dataset being collected while the first and second control signals are following the first and second functional forms. a controller configured to output first and second control signals to the first and second laser sources, the first and second control signals following first and second functional forms over each of one or more scan periods, wherein the first and second functional forms are defined as a coordinated pair to continuously or quasi-continuously tune the frequencies of the first and second frequency combs over a defined fraction of their free spectral ranges while keeping the frequency range of the third frequency comb within the bandwidth of the sample detector; and a data acquisition module arranged to collect a dataset of data points from the sample detector over each scan period, the or each dataset being collected while the first and second control signals are following the first and second functional forms.