The Raman measurements are widely applied to get molecular information and in case of cultural heritage materials, the technique is used to identify both organic and inorganic compounds. Our laboratory-made device has the advantages to be a flexible system, based on a 785-nm CW laser source and a spectrometer coupled to a cooled Si-based CCD camera. Raman signal can be detected in the spectral range 130–3000 cm-1 with a spectral resolution close to 10 cm-1. Two different optical probes can be alternatively used, depending on the desired spatial resolution and size of the field of view.

Macro-probe

The macro-probe Raman works in backscattering mode, delivering the excitation light to a point of interest of 500 μm in diameter at a working distance of 30 cm. The mapping capabilities of the device allow the raster scanning of an area of interest within a field of view 65 x 65 mm2. Time-measurement is appreciable: for a map of 5 mm2 in size (with a step of 0.25 mm) the estimated time is about 30 min. A post-processing method (correlation of a triangular template) allows to the reconstruction of Raman map in selected spectral window.

Micro-Probe

The micro-probe can detect Raman spectra at high signal-to-noise-ratio on selected spots of 50 μm in diameter at a working distance of about 3 mm. The acquisition time usually ranging between 5 and 15 s and the irradiance on sample is set between 700 and 3500 and W cm-1. The micro-probe is typically applied for point analysis and for line-scanning analysis along the sample. In the latter case, the micro-probe head can be coupled to a micrometric linear translation stage.

The TRPL analyses are particularly useful to discriminate amongst different luminescence phenomena occurring in complex materials and as non-invasive methodology for investigate optical properties of pigments. Our device is based on UV pulse stimulation, emitting sub-ns pulses (Q-switching Nd:YAG laser)at repetition rate of 100 Hz. The laser light is delivered to the sample and an optical probe allows the excitation of the PL signal from sample surface in a circular spot of 1 mm in diameter and an average power density of 70 mW/mm2. The PL emission from samples is collected and resolved by a spectrometer (Acton Research 2300i, focal length = 300 mm, f/4 aperture) enable to record in the spectral range 380-750 nm. The time resolved measurements are made possible by the use of a gated intensified camera (C9546-03, Hamamatsu Photonics, Japan) that can record the PL intensity at selected time delay and with a selected gate window (minimum 3 ns). The result is a TRPL dataset in which the rows represent the PL spectra recorded within temporal gates (quoted as gated spectra thereafter) and the columns represents the emission decay kinetic in spectral windows. The kinetic data are normally fitted to a multi-exponential decay model (with a maximum of three components), using a nonlinear least square method. The effective lifetime is calculated as the average of the lifetimes weighted over the number of photons originating from each decay path.

The stratigraphy of painting is often reach of information about the artistic technique and materials. This microscope put together the advantages of UV light stimulation with the time-resolved method for investigate the sub-layers luminescence emission and identify the presence of different components. Our developed system is based on a Q-switching laser source (FTSS 355-50, Crylas GmbH), emitting sub-ns pulses at 355 nm, and on an intensified camera (C9546-03, Hamamatsu Photonics), capable of gated detection with a temporal width adjustable from few ns to the continuous mode. Beside the excitation laser and the image detector, the set-up comprises an optical system, specifically designed for imaging the head of the laser output optical fiber on the sample stage with an uniformly illuminated field of view, independent from the employed objective. The optical system, made of two collecting lenses and a finite conjugate reflective 15X objective (ReflX™ Objectives, Edmund Optics GmbH), allows the illumination of a field of view of 0.9 mm in diameter. The spatial distribution of the PL signal emitted by the sample and collected by the microscope objective is then detected by the time-gated image intensifier. The system is completed with an excitation filter (FL355-10 Thorlabs Inc.), a dichroic filter (LPD01-355RU, Semrock) and a set of 10 band pass transmission filters (FKB-VIS-40, Thorlabs Inc.) mounted on a filter wheel in front of the gated camera. The transmission filters allows the detection of the PL emission in selected spectral bands (40 nm FWHM) within the spectral range between 380 and 870 nm. The spatial sampling pitch of the whole device, which is essentially limited by the spatial resolution of the image intensifier (57 lp/mm), has been estimated as 0.9 um in lateral size.

Fluorescence Lifetime Induced Imaging is largely applied for non-invasive optical application especially on extended artwork, like painting, poster and statue. Our device takes the advantages of the use of a time-gated intensified camera (C9546-03, Hamamatsu Photonics, Japan), capable of an acquisition gate with a temporal width adjustable from 3 ns to continuous mode. UV excitation is provided by a frequency-tripled diode-pumped Nd–Yag laser (FTSS 355-50, Crylas GmbH, Germany), emitting 1-ns pulses at 355 nm. The laser beam is magnified with suitable optics in order to uniformly illuminate a circular area close to 25 cm in diameter, leading to a typical fluence per pulse kept below 140 nJ cm−2. The kinetic of the emission is reconstructed by recording its intensity at different delays with respect to excitation pulses by employing a home-made trigger electronic device and a digital delay generator (DG535, Stanford Research Systems, USA).