14A1　BM - IR Microscopy

Performance

The brightness of the synchrotron radiation source is more than two orders higher than that of 2000K blackbody radiation source in the mid-IR range as shown in Figure 1. The infrared synchrotron radiation source was focused and collimated by using the optical system of the front end of the infrared beamline. The infrared beam size focused by using a 32× confocal Cassegrain objective is about 13 × 10 μm² (FWHM); however, the focused beam size of 2000K blackbody radiation source is about 50 × 30 μm² as shown in Figure 2. Ultrahigh S/N ratio of the spectrum can be easily achieved as using infrared synchrotron radiation; however, a poor S/N ratio is expected as using blackbody radiation source especially the focused beam size goes close to diffraction-limit wavelength as illuminated in Figure 3.

Figure 1. The brightness of the TLS 14A IR beamline and 2000 K blackbody radiation source.

Source	(A) Infrared synchrotron light	(B) 2000 K blackbody radiation
FWHM	13 x 10 mm²	50 x 30 mm²
Intensity	~30000	~1200

Figure 2. The focused infrared beam size on an Al-coated glass slide. (A) infrared synchrotron light source and (B) 2000 K blackbody radiation source.

Figure 3. Comparison of the S/N ratio of FTIR spectra of biomedical tissue section sample using synchrotron light source and blackbody radiation source with focused beam size of 10 × 10 μm² and 20 × 20 μm². Herein FTIR spectra are acquired by accumulating 16 scans with spectral resolution of 4 cm^-1 in the range of 3600-900 cm^-1.

Rejection high-frequency noise using logic gating

The top-up mode is the standard mode of operation at the National Synchrotron Radiation Research Center. Running constant beam current beamlines can take the advantage of the higher flux of photon, brightness and constant heat load as data acquisition. However, a damping noise-induced as injecting electron bunch into storage ring from the boost ring always makes a random interference in the mid-infrared range during the course of top-up mode operation. In order for eliminating the spectral noise as electron injection, an innovative gating system was constructed and which is to generate a trigger pulse to steer the data acquisition program (OMNIC^TM) controlling the endstation of infrared microspectroscopy. The gating module and the trigger status of the end-station of infrared microspectroscopy are exhibited in Figure 4.

Figure 4. The illustration of the logic control timing diagram of the gating circuit for the top-up mode operation, where the reinjection period is 60 seconds and the photo (upper right) is the home-built gating control system.

The electron damping noise is eliminated in the FTIR spectra of the biomedical tissue section sample as data acquisition coupled with the gating system as presented in Figure 5. However, the more number of spectral scans for a spectral acquisition, the less interference was observed in the spectra and which seemed to be less affected by electron injection as top-up mode operation as shown in Figure. 5(C).

Figure 5. The efficiency of coupling the home-built gating system. FTIR spectra are acquired by steering data acquisition program with and without the gating system during the course of a top-up mode operation, where spectral data were collected with spectral resolution of 4 cm^-1 and accumulated (A) 4 scans (B)16 scans (C) 64 scans, respectively. m