Fig. 3: Two setups for varying a laser beam diameter.
From: Simple experimental procedures to distinguish photothermal from hot-carrier processes in plasmonics
a Constant-irradiance setup: 4f optical configuration enabling the setting of an illumination diameter D1 at the sample location S by adjusting the diaphragm diameter D2, according to the relation \({{D}}_{\mathrm{1}}{{ = D}}_{\mathrm{2}}\cdot{{f}}_{{1}}{{/f}}_{{2}}\). Note that for the 4f configuration to be appropriately used, the optical power density impinging on the diaphragm D has to be uniform, not Gaussian. b Constant-power setup: optical configuration, similar to a when removing lens L2, enabling the setting of an illumination diameter D1 at the sample location S, by adjusting the displacement δx of L1, according to the relation \({{D}}_1 = \delta {{x}}\cdot{{D}}_2{{/f}}_1\). Note that L1 can be the objective lens of a microscope
