$$\begin{aligned}
\mathscr{L}\{f(t)\} &=\int_{0}^{1} t e^{-s t} d t+\int_{1}^{\infty} e^{-s t} d t=\left.\left(-\frac{1}{s} t e^{-s t}-\frac{1}{s^{2}} e^{-s t}\right)\right|_{0} ^{1}-\left.\frac{1}{s} e^{-s t}\right|_{1} ^{\infty} \\
&=\left(-\frac{1}{s} e^{-s}-\frac{1}{s^{2}} e^{-s}\right)-\left(0-\frac{1}{s^{2}}\right)-\frac{1}{s}\left(0-e^{-s}\right)=\frac{1}{s^{2}}\left(1-e^{-s}\right), \quad s>0
\end{aligned}$$