Device for thermal diffusivity analysis of a solid-state sample that partially reflects light, characterized in that comprises: - a pump laser with a beam propagation ratio, preferably smaller than 1.2, with a wavelength range between λ pump = 250-1500 nm, and with its power modulated to a harmonic waveform, that generates a pump beam, - optical elements that modify the spatial intensity distribution of the pump laser such that, after focusing with a lens, the image of the pump laser results in a narrow, lower than 10 μm, line-shaped image with a length ranging between 400 μm and 1000 μm, and with uniform intensity distribution, - a probe laser with a wavelength between λ probe = 250-1500 nm and an intensity constant in time, generating a probe beam, - an electronic device to modulate harmonically the output power of the pump laser between 10 Hz and 100 kHz, - a deflectable mirror, following the pump laser, to control the offset between the pump beam and probe beam, - a first beam splitter following the probe laser that couples the probe beam into an optical axis and, at the same time, generates a sample of the probe beam, - a second beam splitter following the deflectable mirror that couples the pump beam into the optical axis, - an objective lens, following the beam splitters (10, 7), intended to focus the beams (24, 25) on the sample, generating a pump beam back reflection and probe beam back reflection, - a first and a second notch-filters (15, 16), that receive the pump beam back reflection and probe beam back reflection from the sample, and selects the pump or probe wavelength, - an AC-coupled balanced detector, placed to receive the pump beam back reflection and probe beam back reflection in a first input from the notch-filters (15, 16) and the sample of the probe beam in a second input from the ND filter, and is configured to generate a frequency modulated voltage arising from the thermal oscillations on the surface of the sample, - a neutral density filter to control the power of the probe beam at the secondary input of the balanced detector, and - a lock-in amplifier, connected to the output channel of the detector. - a pump laser with a beam propagation ratio, preferably smaller than 1.2, with a wavelength range between λ pump = 250-1500 nm, and with its power modulated to a harmonic waveform, that generates a pump beam, - optical elements that modify the spatial intensity distribution of the pump laser such that, after focusing with a lens, the image of the pump laser results in a narrow, lower than 10 μm, line-shaped image with a length ranging between 400 μm and 1000 μm, and with uniform intensity distribution, - a probe laser with a wavelength between λ probe = 250-1500 nm and an intensity constant in time, generating a probe beam, - an electronic device to modulate harmonically the output power of the pump laser between 10 Hz and 100 kHz, - a deflectable mirror, following the pump laser, to control the offset between the pump beam and probe beam, - a first beam splitter following the probe laser that couples the probe beam into an optical axis and, at the same time, generates a sample of the probe beam, - a second beam splitter following the deflectable mirror that couples the pump beam into the optical axis, - an objective lens, following the beam splitters (10, 7), intended to focus the beams (24, 25) on the sample, generating a pump beam back reflection and probe beam back reflection, - a first and a second notch-filters (15, 16), that receive the pump beam back reflection and probe beam back reflection from the sample, and selects the pump or probe wavelength, - an AC-coupled balanced detector, placed to receive the pump beam back reflection and probe beam back reflection in a first input from the notch-filters (15, 16) and the sample of the probe beam in a second input from the ND filter, and is configured to generate a frequency modulated voltage arising from the thermal oscillations on the surface of the sample, - a neutral density filter to control the power of the probe beam at the secondary input of the balanced detector, and - a lock-in amplifier, connected to the output channel of the detector.