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Yuka Iwaya, Takayuki Wakui
An UV-Vis spectrophotometer is an instrument that measures transmission, refl ection, and absorption spectra in the ultraviolet (200-380 nm) and visible (380-780 nm) regions. These instruments are used to make measurements in a wide variety of settings, including a cademic studies, research and development, and quality control in fields such as material science, environmental science, pharmaceuticals, and biology-related disciplines. UV-Vis-NIR spectrophotometers extend the range of measurable wavelengths to the near infrared (780-3300 nm*1), and have been used for purposes such as double-beam light measurements capable of correcting baseline drift, as well as in double monochromators optimized for measuring samples with low stray light and high absorption.1) For these reasons, UV-Vis-NIR spectrophotometers exhibit high stability and accuracy and have been used for a variety of purposes, including not only characterization of optical properties of elements such as camera lenses and laser windows but also research and development and quality control for optical devices such as high-density data-recording disks and vehiclemounted sensors.
In recent years, demand has grown within the field of optical thin films such a s band-pass and notch filters for measurements of highly absorbing samples in specific wavelength regimes with even higher accuracy and reduced stray light. To this end, in this article we present the UH4150AD spectrophotometer (Figure 1), a new product developed specifi cally for high absorption and ultra-low-transmissivity measurements.
Fig.1 The UH4150AD spectrophotometer
In this section we discuss three major features of the UH4150AD.
Since the adoption of a new grating-grating double monochromator reduces stray light in the spectrometer, the instrument is capable of increasing the absorbance range and measuring up to absorbance 8.
By equipping the UH4150AD with an integrating sphere, it is possible to make measurements with a parallel flux, as with the predecessor instrument.*3 In particular, with a parallel flux, the incidence angle is roughly uniform over the sample, allowing high-accuracy measurements of mirror reflection (Figure 2).
Fig.2 Schematic illustrations of parallel flux and concentration of light flux.
The sample chamber in the UH4150AD uses the same structure as its predecessor instruments. This allows large samples to be placed in the chamber and retains the convenience of allowing a variety of accessories for previousgeneration instruments to be used. By combining detectors and sample holders in various ways, the construction of the system in response to various demands is possible. (Figure 3).
Fig.3 Typical detector choices
In this example, we use the UH4150AD to measure concentration series of Co(NO3)2 aqueous solutions and verify the linearity of the resulting absorbance curve. Figure 4 shows absorption spectra for aqueous solutions of Co(NO3)2, while Figure 5 shows the relationship between absorbance and concentration at a wavelength of 510 nm. The absorbance vs. concentration curve is seen to maintain good linearity (R2=0.999) all the way up to absorbance 8.
Fig.4 Absorption spectra for Co(NO3)2
Fig.5 Calibration curve for Co(NO3)2 aqueous solutions at wavelength 510 nm
In this example we measure absorption spectra for three filters with different absorbances and compare the absorption spectrum obtained with all three fi lters combined to the sum of the individual spectra measured for each fi lter in isolation. Absorption spectra are shown in Figure 6. The measured spectrum is in excellent agreement with the predicted spectrum.
Fig.6 Filter absorption spectra
The UV-Vis-NIR UH4150AD spectrophotometer is custom designed for measurements of high-absorbance, ultralow-transmittance samples. It offers more reliable measurements for characterization and quality control of optical thin films such as bandpass and notch filters.
Optical Instrument Design Department
Hitachi High-Tech Science Corporation