Abstract
.We have developed a photoacoustic (PA) sensor using a low-power, continuous- wave laser and a kHz-range microphone. The sensor is simple, flexible, cost-effective, and compatible with commercial optical microscopes. The sensor enables noncontact PA measurements through air, whereas most current existing PA techniques require an acoustic coupling liquid for detection. The PA sensor has three main components: one is the chamber that holds the sample, the second is a resonator column used to amplify the weak PA signals generated within the sample chamber, and the third is a microphone at the end of the resonator column to detect the amplified signals. The chamber size was designed to be as the thermal diffusion length and viscous-thermal damping of air at room pressure and temperature are 2 and 1 mm, respectively. We numerically and experimentally examined the effect of the resonator column size on the frequency response of the PA sensor. The quality factor decreased significantly when the sample chamber size was reduced from to due to thermos-viscous damping of the air. The quality factor decreased by 27%, demonstrating the need for optimal design for the sample chamber and resonator column size. The system exhibited noise equivalent molecular sensitivity (NEM) per unit bandwidth () of or or 33 zeptomol, which is an improvement of 2.2 times compared to the previous system design. This PA sensor has the potential for noncontact high-resolution PA imaging of materials without the need for coupling fluids.
Highlights
The photoacoustic (PA) effect was first observed in the year 1880 by Alexander Graham Bell.[1]
The PA effect was used in spectroscopy techniques throughout the mid-1900s, but the invention of the laser has significantly changed the paradigm of the PA technique because of the improved sensitivity provided by pulsed laser excitation.[2,3,4,5,6,7,8,9,10,11,12,13]
This study investigates the use of the PA sensor in OR-Photoacoustic microscopy (PAM) applications, with a focus on cell design using numerical simulation techniques and experimental verification
Summary
The photoacoustic (PA) effect was first observed in the year 1880 by Alexander Graham Bell.[1] The PA effect was used in spectroscopy techniques throughout the mid-1900s, but the invention of the laser has significantly changed the paradigm of the PA technique because of the improved sensitivity provided by pulsed laser excitation.[2,3,4,5,6,7,8,9,10,11,12,13]. Photoacoustic microscopy (PAM) is a hybrid imaging modality that uses an optical technique for excitation and an acoustic technique for detection. The lateral resolution of AR-PAM depends on the acoustic focus of the transducer which is of the order of tens
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