High Axial Resolution Raman Probe Made of a Single Hollow Optical Fiber

Abstract

A ball lens mounted hollow optical fiber Raman probe (BHRP) consisting of a single hollow optical fiber (HOF) and a micro-ball lens was developed for performing a high axial resolution and high-sensitivity remote Raman analysis of biomedical tissues. The total diameter of the probe head is 640 microm. The BHRP is useful in the measurement of thin-layered tissues that are in contact with the probe's surface because the probe has a limited depth-of-field optical property. An optical calculation study suggested that it is possible to vary the probe's working distance by selecting different materials and diameters for the ball lens. Empirical studies revealed that this probe has a higher axial resolution and a higher sensitivity than an HOF Raman probe without the ball lens. The spectrum of a mouse stomach measured with the BHRP had better quality and considerably lower noise than that measured with a conventional Raman microscope. These results strongly suggest that the BHRP can be used effectively in biomedical applications.

Fiber-Optic Raman Probes for Biomedical and Pharmaceutical Applications

“…One is made of bundled fibers and has a diameter of 600 μm [28]. The other is made of HOF with a ball lens and has a diameter of 640 μm [37].…”

“…A single HOF can be used bi-directionally, i.e., for sending the excitation light and for collecting the Raman scattered light [34]. However, the low NA, which causes low collection efficiency, is the major disadvantage of an HOF Raman probe [34,37]. Addition of a ball lens to the distal end of the HOF Raman probe (BHRP; Fig.…”

“…Addition of a ball lens to the distal end of the HOF Raman probe (BHRP; Fig. 2.7) resulted in a promising design for a miniaturized Raman probe [35,37]. The probe is made of a single HOF that transmits both excitation and collected light.…”

“…Then, the sheath was glued to the distal end of the HOF. A fiber chuck was attached to the other end of the HOF to attach to the fiber coupling stage [37]. The total diameter of the probe head was 640 μm.…”

“…An advantage of the BHRP is that it is possible to control the working distance (WD) by selecting materials with different refractive indices and/or varying the diameter of the ball lens [37]. Since the spatial resolution of the BHRP is limited by the spherical aberration of the ball lens and the NA of the HOF, as described in Fig.…”