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TECHNOLOGY 41
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The samples were prepared for impregnation by placing an increasing number of laser shots, which were delivered in
them vertically in the solution, one above the other. the same place, and then recording the number of spectra
They were loaded with glass beads to prevent the wood created by subsequent laser shots.
samples from floating to the surface. Wood impregnation was The focal length of the focusing lens was 150 mm. The

performed using a single vacuum and an ultrasound. Vacuum distance of the lens from the wood was set to 140 mm to
impregnation was performed in a vacuum dryer model 1445- avoid an accidental laser breakdown in air.
2 (with a pump model V-700. The impregnation was carried The geometry of the sample irradiation was as follows: the
out under the following conditions: vacuum 190 mbar, time laser beam was perpendicular to the wood sample surface,
30 min, temperature 28 deg C. i.e., the angle of incidence calculated from the normal to the
Then, the pressure in the chamber was brought to surface was 0 degree, while the spectra were collected at
atmospheric pressure, and the samples were left in the solution the angle of approximately 60 degrees to the surface, i.e.,
for another 30 minutes. The samples were removed from the 30 degrees from the normal to the surface.
graphene oxide dispersion and left to dry. The diameter of the laser spot focal point on the wood

Pressureless impregnation was performed using an ultrasonic surface with the assumed dimensions of the distance between
bath. The impregnation process was carried out under the the lens and the wood was approximately 0.1–0.3 mm,
following conditions: time 30 min, temperature 22 deg C. After depending on wood age (late or early one). The laser fluence
completing the process, the samples were left in the solution was 0.14 J/mm2. The ablation rate was between 0.08 ÷ 0.12
for another 30 minutes. The samples were removed from the mm3/pulse and 0.71 ÷ 1.06 mm3/pulse for ablation craters
graphene oxide dispersion and left to dry. of 10–15 µm in depth.
The wood samples were coded as follows: Since there are visible divisions between early and late

• C—Control wood (not treated), wood (annual growth) in the anatomical structure of pine
• GO—Wood impregnated with GO using the single-vacuum wood, the profile of element spectra was analysed in the
method, and early and late wood layers.
• GOU—Wood impregnated with GO using the ultrasonic Due to the differences in the cellular structure in the early
method. and late wood zones, there is a probability of quantitative
and qualitative differences in the graphene oxide incorporated
LIBS studies were performed based on the experimental into the wood layers of the zones produced in the spring
setup and research procedure presented in the publication. (earlywood) and summer (latewood) periods.
The studies used a pulsed Nd:YAG laser. The wavelength In order to identify wood samples in the LIBS study,

was 1064 nm, the pulse energy was 10 mJ, and the pulse
duration was 4 ns. Plasma radiation was recorded using an
echelle ESA 4000 spectrometer.
The spectrometer enabled the detection of spectra in time furnitureproduction.net
windows from 20 ns to 16 ms in the 200–800 nm range. The
detector was a Kodak KAF 1001 CCD matrix with an ICCD
amplifier. The spectral resolution of the entire detection system

was λ/Δλ~20,000.
The analysis of stratigraphic spectra consisted of conducting