Fig. 1. Detection mechanism of the polymer probe. The schematic of the probe is illustrated in the upper left panel of the figure, while the Q-factor measurement is presented in the upper right panel. US: ultrasound.

Fig. 2. (a) Overall circuit structure of the light source. (b) Temperature control structure of the DFB laser. (c) Results of temperature tuning for the DFB laser, showing the variation of the output wavelength with temperature. (d) Linear relationship between the DFB laser’s output wavelength and temperature. The red line represents the variation in peak intensity of DFB during this process. (e) Characterization of the DFB laser’s temperature control, illustrating the response time of the light source to temperature change commands. Top-right inset: response time for rapid, small-scale temperature variations. Bottom-right inset: temperature fluctuations when stabilized at a preset temperature.

Fig. 3. (a) Physical image of the packaged probe. The subfigure is a microscopic image of the probe before encapsulation. (b) Normal mode scanning result of the probe mode. (c) Thermal broadening scanning result of the probe mode. (d) Logical diagram of the mode-locking process. (e) PA signal of the silver film sample, detected using the locked polymer probe. (f) Bandwidth of the polymer probe obtained from the Fourier transform of (e).

Fig. 4. (a) Schematic diagram of the PA signal measurement system. (b) PA signal response of the hydrophone. (c) PA signal response of the polymer microcavity ultrasound probe. (d) PA signal response of the silica microcavity ultrasound probe.

Fig. 5. (a) PA signal responses of the polymer microcavity ultrasound probe at different crystal violet concentrations. (b) Photograph of the experimental setup. CVA, circular variable attenuator; ID, iris diaphragm. (c) Crystal violet solutions with different concentrations, decreasing by a factor of 10 from left to right. The far-right sample is pure water. (d) Relationship between the PA signal’s P-P value and the crystal violet concentration.