The primary objective of this work was to develop and optimize the calibration techniques for ultrasonic hydrophone probes used in acoustic field measurements up to 100
MHz. A dependable, 100
MHz calibration method was necessary to examine the behavior of a sub-millimeter spatial resolution fiber optic (FO) sensor and assess the need for such a sensor as an alternative tool for high frequency characterization of ultrasound fields. Also, it was of interest to investigate the feasibility of using FO probes in high intensity fields such as those employed in HIFU (high intensity focused ultrasound) applications. In addition to the development and validation of a novel, 100
MHz calibration technique the innovative elements of this research include implementation and testing of a prototype FO sensor with an active diameter of about 10
μm that exhibits uniform sensitivity over the considered frequency range and does not require any spatial averaging corrections up to about 75
MHz. The results of the calibration measurements are presented and it is shown that the optimized calibration technique allows the sensitivity of the hydrophone probes to be determined as a virtually continuous function of frequency and is also well suited to verify the uniformity of the FO sensor frequency response. As anticipated, the overall uncertainty of the calibration was dependent on frequency and determined to be about ±12% (±1
dB) up to 40
MHz, ±20% (±1.5
dB) from 40 to 60
MHz and ±25% (±2
dB) from 60 to 100
MHz. The outcome of this research indicates that once fully developed and calibrated, the combined acousto-optic system will constitute a universal reference tool in the wide, 100
MHz bandwidth.