In this paper

a series of calibration-free temperature measurement methods based on light-induced thermoelastic spectroscopy (LITES) are proposed for the first time. These techniques utilize the steady-state and transient response characteristics of the quartz tuning fork (QTF)

namely

the calibration-free LITES (CF-LITES) and calibration-free heterodyne LITES (CF-H-LITES) methods. Four methods

first harmonic (1f) difference signal to normalize the second harmonic (2f) fundamental signal (method I

2ffund/1fdiff)

1f overtone signal to normalize the 2f fundamental signal (method II

2ffund/1fover)

1f heterodyne difference signal to normalize the 2f heterodyne fundamental signal (method III

2f-Hfund/1f-Hdiff)

and 1f heterodyne overtone signal to normalize the 2f heterodyne fundamental signal (method IV

2f-Hfund/1f-Hover)

for simultaneously detecting 1f and 2f within the frequency response range of the QTF are proposed to achieve calibration-free measurement. A self-designed T-shaped QTF with low fundamental and overtone frequencies was used to increase the energy accumulation time

thereby enhancing the sensor signal level. A 3-stage tube furnace was adopted to verify the performance of these 4 methods. Experimental results showed that the errors for the 4 methods were less than 4%

with a standard deviation below 11 °C. Furthermore

the calibration-free method

which employs normalization of the 2f signal with the 1f signal

effectively mitigates the impact of laser beam jitter and power fluctuations on detection performance. A superior performance can be obtained by adopting the CF-H-LITES technique based on method IV. It not only has excellent detection performance but also reduces the measurement period to 4 s

which is about 5 times faster. This development shows substantial promise for expanding the application of the CF-LITES and CF-H-LITES techniques in harsh environments.