Echelle optics

The measurements were performed using a Thermo Elemental IRIS Inductively Coupled Plasma Atomic Emission Spectrometer (ICP-AES). A 2 kW crystal-controlled radio frequency (RF) generator operating at 27.12 MHz powers the plasma source. An Echelle optical system with a 381-mm focal length diffracts the light from the plasma source before it is focused onto the Charge Injected Device (CID) camera detector [4]. 

Solid sampling with a NdiYAG laser for direct analysis with ICP-AES using an echelle optical system in conjunction with a solid-state detector is a straightforward technique [70]. 

Florek S. V., Niemax K. and Becker-Ross H. (2004) Element-specific detection of gas chromatographic eluates by near-infrared echelle optical emission spectrometry on microwave-induced plasmas, Spectrochim. Acta,... 

A modern spectrophotometer (UV/VIS, NIR, mid-IR) consists of a number of essential components source optical bench (mirror, filter, grating, Fourier transform, diode array, IRED, AOTF) sample holder detector (PDA, CCD) amplifier computer control. Important experimental parameters are the optical resolution (the minimum difference in wavelength that can be separated by the spectrometer) and the width of the light beam entering the spectrometer (the fixed entrance slit or fibre core). Modern echelle spectral analysers record simultaneously from UV to NIR. 

We have observed three subgiants HD 23249 (KO), HD 198149 (KO), HD 222404 (Kl) and three dwarfs HD 10780 (KO), HD 4628 (K2), HD 201091 (K5), on 2002 November 28 and 29, with the high-resolution cross-dispersed echelle spectrograph SOFIN, mounted on the Nordic Optical Telescope (NOT). They are in the solar neighbourhood (< 15 pc), are very bright (V < 6) and have modest projected rotational velocities (v sin i < 4 km s 1) to limit blends between spectral lines. They also do not present any evidence for emission (or a moderate one, as in the case of the three dwarfs) in the core of Ca II H and K lines. 

One optical arrangement in an echelle-based monochromator. In this case a Schmidt cross-disperser is used to disperse the UV light instead of The prism which is used for visible light only. This results in better transmission in the UV (reproduced with permission from the Perkin Elmer Corporation). 

Fig. 1 Optical diagram of the prototype system model. The drawing is not to scale and is not to be considered an optical ray diagram. The principal dispersing element is a coarse echelle ruled grating 20 x 40 cm wide. Theoretical double-pass resolution at four normal slits is approximately 0.095 cm-1 actual achievable resolution is approximately 0.009 cm-1.

To isolate specific emissions of the analyte being analysed (i.e. optical transitions), a high quality optical set-up is required. Dispersive systems using planar, concave or echelle gratings are used in classical spectrophotometers or spectrographs (Figs. ll.lO and 15.6). 

Figure 15.6-— Principle of dispersion in the focalplane using an arrangement comprising an echelle grating and prism. For clarity, the associated optics (collimating and focusing lenses) are not shown in the top figure. In this set-up, the entrance slit is not very high.

Figure 15.7—Optical diagrams for a spectrophotometer with an echelle grating. Model PU 7000 optical system (reproduced by permission of Philips). All spectral lines are captured, which allows a more complete study of the sample. The dynamic range of these instruments is still lower than that of a PMT.

The LPA instrument of Mount (42) uses a XeCl laser to monitor absorption near the Qi(S) line group. The laser beam, expanded in a telescope to an initial area of 150 cm2, is reflected from a retroreflector array for a total optical path of 20.6 km. The returned beam and a portion of the outgoing beam follow symmetric paths through an echelle spectrograph to a pair of photodiode array detectors, thus providing both I and Z0 spectra for the... 

Switch-Board Optics. The preceding discussion has summarized the various approaches which have been taken to achieve a practical spectrometer for SMA. The direct reader, the vidicon detector, and the development of image device/echelle systems... 

The multielement detection limits with the echelle/image dissector are comparable to, or better than, single element detection limits reported for a silicon vidicon and conventional optics. Detection limits for Cr, Cu, and Mn with the echelle/ image dissector compare favorably with single element data reported for a conventional atomic absorption instrument with a photomultiplier detector, but detection limits obtained here for Ni and Co are higher by factors of 10 or more than for the conventional instrument. The echelle/image dissector system should be adaptable to a so-called flameless atomizer and be subject to the same improvements in sensitivities and detection limits as conventional detector systems. 

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