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Schematic representation of a softwood. Radial-tangential (RT) and longitudinal-tangential (LT) sections can be prepared with a microtome. The shape of samples for micromechanical testing is highlighted and the loading directions are labelled.
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Adult wood from a block of a 100-year-old Norway spruce (Picea abies) was microtomed into radial-tangential (RT) and longitudinal-tangential (LT) slices, further called RT- and LT-sections (see Figure 1). The femtosecond laser unit (Origami 10 XP, Onefive GmbH, Regensdorf, Switzerland, Figure 2 (1)) operates with a laser pulse duration of 318 fs, a maximum average output power of 4 W at 100 kHz pulse repetition rate and a maximum pulse repetition rate of 1 MHz.
Schematic of the laser setup. The laser pulses are generated by the femtosecond laser unit (1). The laser is guided through the beam expander (2), which determines the working distance in the laser chamber. The deflection mirrors (3 and 4) guide the laser pulse to a specific position. The f-theta lens (5) enables laser operation on a flat image plane.
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FIB machining and SEM analysis without leaving the vacuum state if required. Figure 2 shows a schematic diagram of the experimental setup. The femtosecond laser unit (Origami 10 XP, Onefive GmbH, Regensdorf, Switzerland, Figure 2 (1)) operates with a laser pulse duration of 318 fs, a maximum average output power of 4 W at 100 kHz pulse repetition rate and a maximum pulse repetition rate of 1 MHz. First, the laser beam is guided through the beam expander (Figure 2 (2)), which consists of a dispersal and a collecting lens. Following the beam expander in the laser beam path, a scan unit (intelliscan III 10, SCANLAB AG, Puchheim, Germany) consisting of two rotatable mirrors (Figure 2 (3, 4)) guides the laser beam into the laser processing chamber. Eventually, an f-theta lens (Figure 2 (5)), focuses the laser beam onto a flat image plane and provides a constant focal diameter across the sample surface.
Optical micrograph of a set of four tensile samples prepared from a LT-section with the tangential direction parallel to the tensile axis. The sample had a width, w, of 70 mum and a length, l, of 400 mum. The processing time was about 8 min.
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Following the beam expander in the laser beam path, a scan unit (intelliscan III 10, SCANLAB AG, Puchheim, Germany) consisting of two rotatable mirrors (Figure 2 (3, 4)) guides the laser beam into the laser processing chamber.
SEM micrograph of two samples prepared with the femtosecond laser from a RT-section with the radial direction parallel to the tensile axis.
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Following the beam expander in the laser beam path, a scan unit (intelliscan III 10, SCANLAB AG, Puchheim, Germany) consisting of two rotatable mirrors (Figure 2 (3, 4)) guides the laser beam into the laser processing chamber.
SEM micrographs of a femtosecond laser-processed surface on a LT-section. (a) Next to the laser kerf, the intact S3 layer with pits is visible; (b) larger magnification of the laser incised surface.
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Eventually, an f-theta lens (Figure 2 (5)), focuses the laser beam onto a flat image plane and provides a constant focal diameter across the sample surface.