Tunable terajet realization by a liquid-injected hollow microsphere and application for terahertz scanning imaging

Terajets (TJs) have demonstrated significant potential for terahertz (THz) high-resolution imaging and detection. However, generating tunable TJs remains challenging, limiting the application of TJs in broader scenarios. In this work, we report a simple, precise, and flexible method to generate dynamically tunable TJs using a liquid-injected hollow microsphere (LIHM). By adjusting the volume of liquid injected into the LIHM, sub- or hyper-hemispherical interfaces of varying heights are formed inside the microsphere, enabling fine control over key properties of the TJs. The generation of TJs with tunable focal length, effective length, and full-width at half-maximum is confirmed by both numerical simulations and experiments. To demonstrate the utility of tunable TJs in THz imaging, we show that a LIHM-coupled imaging system can switch between extended depth of field imaging and high-resolution imaging, and adaptable resolving capabilities at identical sample locations can be realized, which highlights the adaptability of the LIHM to diverse imaging scenarios. This low-cost and expertise-minimized method for generating tunable TJs paves the way for broader practical application in THz technology.