Photoacoustic (PA) imaging has been used to image soft tissue due to its high contrast and high spatial resolution. The
generation of PA signal is based on the object's absorption characteristic to the emitted electromagnetic energy.
Typically, a Q-switched Nd:YAG laser providing mJ pulse energy is suitable for biomedical PA applications. However,
such laser is relatively bulky and expensive. An alternative way is to use a diode laser. A diode laser can generate laser
pulse at much higher pulse repetition frequency (PRF). However, the output power of the diode laser is too low for
effective PA generation. One method to overcome this problem is to increase the transmission energy using coded
excitation. The coded laser signals can be transmitted by a diode laser with high PRF and the signal intensity of the
received signal can be enhanced using pulse compression. In this study, we proposed a chirp coded excitation algorithm
for a diode laser. Compared to Golay coded excitation seen in the literature, the proposed chirp coded excitation requires
only a single transmission. Chirp-coded PA signal was generated by tuning the pulse duration of individual laser pulses
in time domain. Result shows that the PA signal intensity can be enhanced after matched filtering. However, high range
side-lobes are still present. The compression filter is an important tool to reduce the range side-lobes, which is subject to
further investigation.
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