  Temperature field contactless measurements in or at the surfaces of
semitransparent media are a scientific challenge, as classical thermography
techniques based on proper material emission cannot be used. In this work, an
alternative method using infrared thermotransmittance for contactless imaging
temperatures is proposed. To overcome the weakness of the measured signal, a
lock-in acquisition chain is developed, and an imaging demodulation technique
is used to retrieve the phase and amplitude of the thermotransmitted signal.
These measurements, combined with an analytical model, enable the estimation of
the thermal diffusivity and conductivity of an infrared semitransparent
insulator (wafer of borofloat 33 glass) as well as the monochromatic
thermotransmittance coefficient at 3.3 um. The obtained temperature fields are
in good agreement with the model, and a detection limit of $\pm 2^{\circ}$ C is
estimated with this method. The results of this work open new opportunities in
the development of advanced thermal metrology for semitransparent media.
