Optical generation of ultrasound has broad applicability in diagnostic and therapeutic clinical applications. With fibre-optic ultrasound transmitters, ultrasound waves are generated photoacoustically by laser pulses incident on an optically-absorbing coating at the distal end of an optical fibre. Energy from the laser pulses that is not converted to ultrasound raises the temperature of the transmitter coating and surrounding medium. Limiting the maximum temperature is important for tissue safety and the integrity of the transmitter. In this study, we used a finite element thermal model of a fibre-optic ultrasound transmitter to study the influence of three parameters on the temperature rises in the transmitter and the surrounding medium: the laser pulse energy, the laser pulse repetition frequency, and the coating absorption coefficient. To evaluate the validity of the model, the simulation results were compared with thermal imaging experiments of a carbon-polydimethylsiloxane composite-based fibre-optic ultrasound transmitter. Of the studied parameters, the pulse repetition frequency (PRF) has the greatest impact on the temperature rise in the surrounding medium, with a six-fold rise in temperature change resulting from an increase in PRF from 100 Hz to 1 kHz. Our findings have direct applicability to optimising the performance of fibre optic transmitters.