Figure 4.

Temporal response of thermocouple on a 30-nm-thick SiN-membrane to a square-wave optical excitation. (a) Video image of a tightly-focused laser beam onto thermocouple with $\sim 10$ μm spot diameter; λ = 830 nm. (b) Temporal response of thermocouples: (i) to a 3.6 mW laser power at repetition rate f = 2 kHz with a thermocouple on a slide glass and (ii) to 1.8 mW power with thermocouple on a 30-nm-thick SiN-membrane at f = 2, 5, 10 kHz; note different x-axis scales in (b). The fastest switching time was τ = RC = 10 μs with ohmic resistance of thermocouple R = 500 Ω and C = 20 nF. Electronic pre-amplifier of 100× was used for a direct observation by oscilloscope. The estimated max-min ΔT span was 16 K (30.7-to-14.7 K above RT of 22 °C) for the thermocouple on glass and ΔT = 4.1 K for 30 nm SiN-membrane (31.3-to-27.2 K) at 2 kHz; at higher 5 and 10 kHz frequencies the max temperature increase was similar ΔT_max = 30.5 K and min-max span of ∼4 K.