Abstract: The invention provides a method and system to record the absorption of a sample, said method comprising the steps of providing first and second pulsed beam of light on said sample using one or more light beams, said first and second pulsed beam having different spatial definition; measuring the difference in intensity transmitted through and/or reflected by a sample; and generating an image by scanning the sample while making such measurements. The system and method of the invention can work down to resolution of several 100 of nm, affording thus a large improvement in comparison to synchrotron IR imaging that is the closest technique existing today. The advantage versus scanning probe approach is the absence of physical probe, thus suppressing confinement to surface information and removing uncertainty regarding the working behaviour of the probe.

Abstract: To improve the signal-to-noise ratio in trace analysis in gases or plasmas (3) by absorption spectroscopy the wavelength of the analyzing beam of a semiconductor laser (1) is modulated by a frequency f.sub.1 and the absorption length or population density of absorbing particles of the plasma is modulated by a frequency f.sub.2. For the measurement a lock-in amplifier (5) coupled to a photodiode (4) is tuned to the sum or difference frequency of the frequencies f.sub.1 and f.sub.2 or whole-number multiples thereof.