## 1 Introduction
[PERSON] and [PERSON] [19] utilized a micro-scale absorber imprinted on an acetate sheet mounted on a rotating disk, and the rotational velocity was measured in a range of \(\pm\)150 to \(\pm\)1500 mm/s. Their results demonstrated the capability of measuring velocities up to 1400 mm/s with a resolution of \(\pm\)8.0 mm/s. The technique can be extended by considering the beam width of the UST and setting the time delay to 15 ms. However, the measurements were limited to the range of \(\pm\)150 to \(\pm\)1500 mm/s due to non-uniform motor speeds below 150 mm/s. While these measurements were conducted with multiple particles to mimic RBCs in blood, the performance of CC-based PA velocity measurements for a single object has not been adequately evaluated. Previous studies focusing on single particles or objects were conducted for verifying theoretical models [22]. The ability to measure the velocity of individual objects is essential for identifying single cells circulating at different velocities or cell aggregates, and to determine a cell's location in a vessel cross-section [23; 24]. The flow velocity in the microvasculature was estimated to be \(<\)50 mm/s. Since the objective of the PA velocity measurement primarily targets lower speeds in the range of 10 mm/s, it is necessary to investigate the measurement performance for a single object at lower velocities such as in several \(\pm\)10 to \(\pm\)100 mm/s. Additionally the microvasculature exhibits a frequency component corresponding to the heartbeat. This implies that pulsation must be considered when measuring the flow velocity of the microvasculature [25]. In this study, we evaluated the performance and uncertainty associated with PA velocity measurements across a wide range of velocities, including both positive and negative directions. PA signals from micro-scale particles that are employed to simulate RBCs are weak and sensitive to background noise. Particularly in the case of particle clusters in fluid, the dispersion and diffusion of particle clusters, as well as their advection, contribute to the variation of the resulting PA signal pairs, which degrades the measurement performance. To evaluate the measurement performance of the advection due to the motion of the particle cluster, a high signal-to-noise ratio (SNR) and repeatability are required in the experiments. Our objective was to obtain PA signals that are not hidden by noise, which is crucial for the accurate assessment of PA velocity measurements. To achieve this, we employed a GC with a diameter of 2.0 mm as an object, given its efficient light energy absorption capabilities compared with that of RBCs, thereby generating PA signals with a high SNR with sufficient repeatability without the dispersion nor diffusion of particle clusters in fluid. Using a loudspeaker (LS) oscillation for generating repeatable sinusoidal linear motion, the movement of the object was facilitated in the range of \(-\)300 to 300 mm/s. We evaluated the fundamental performance of the measurements and compared them with the reference velocities generated by the LS oscillation. The PA signals were generated from a GC by irradiating it with a pair of laser pulses with a time delay. The time shift between the signals was determined by employing CC in the time-domain, allowing for the calculation of velocity. The LS is capable of generating the velocities in a range of several 10 to 300 mm/s by adjusting the input voltage amplitude and frequency. In the experiment, a function generator was used to synchronize pulse repetition frequency (PRF) and LS oscillations. This synchronization enabled pulse irradiation at arbitrary positions in the LS oscillation by shifting their phases. Furthermore, the results of the measurement performance with a single object can be transferred to the experiment with multiple objects towards the PA flow velocimetry. In the following sections, we outline the methodology, experimental apparatus and procedure, signal processing, results, and discussion.