Echelle

The analytical capabilities of LIBS and LA-MIP-OES were recently noticeably improved by use of an advanced detection scheme based on an Echelle spectrometer combined with a high-sensitivity ICCD (intensified charge-coupled device) detector. 

Abstract This tutorial shows how fundamental is the role plaid by interferences in many of the physical processes involved in astrophysical signal formating and consequently instmmentation. It is obvious in interferometry. Grating spectroscopy is explained within the same framework as Young experiment, and Fabry-Perot filters are explained as Michelson interferometers.Polarization interferences, used in Lyot filters, are discussed, emphasizing the analogy with echelle gratings. 

Figure 11. Left Littrow configuration for an echelle grating. Right example of the layout of orders (labelled by m) on the detector showing the wavelength ranges covered.

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. 

The main detectors used in AES today are photomultiplier tubes (PMTs), photodiode arrays (PDAs), charge-coupled devices (CCDs), and vidicons, image dissectors, and charge-injection detectors (CIDs). An innovative CCD detector for AES has been described [147]. New developments are the array detector AES. With modem multichannel echelle spectral analysers it is possible to analyse any luminous event (flash, spark, laser-induced plasma, discharge) instantly. Considering the complexity of emission spectra, the importance of spectral resolution cannot be overemphasised. Table 8.25 shows some typical spectral emission lines of some common elements. Atomic plasma emission sources can act as chromatographic detectors, e.g. GC-AED (see Chapter 4). 

Figure 3.4 shows (i) a line spectrum (one-dimensional dispersive spec-trographic record), (ii) a spectrometric record, (iii) an interferogram obtained by a Fourier transform spectrometer, and (iv, v) two- and three-dimensional double dispersive spectra recorded e.g. by Echelle spectrometers. In principle, all forms may be obtained by OES. 

Echelle-spectrum), two-dimensional spectrum), three-dimensional... 

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. 

CRIRES stands for CRvogenic Infrared Echelle Spectrograph. 

The Hubble mid-UV echelle spectra extend blueward to 2130 A for hot stars, or to 2380 A or 2885 A for cooler ones. Redward they extend to 3120 A for faint stars, to 2885 A for bright hot stars, and to 3150 A for bright cool stars. These spectra are flux-calibrated, which fixes the mid-UV continuum normalization. 

Fig. 1. Co-addition of four UVES pipeline spectra of NGC 6397/TO201432 (observing dates 2000-06-18 and 22, two spectra per night). The resulting spectrum was arbitrarily normalized at 6410 and 6690 A. As blaze residuals are not properly accounted for in the pipeline order merging, the echelle order pattern is clearly visible in the merged spectrum. With an amplitude of 2 %, these instrumental artifacts do not allow to derive Baimer-profile temperatures to better than 200-300K.

A.J. Korn Rectifying Echelle Spectra - A Comparison between UVES, FEROS and FOCES . In Scientific Drivers for ESO Future VLT/VLTI Instrumentation, ed. by J. Bergeron, G. Monnet (Springer, Heidelberg 2002), pp. 199-204... 

The LIBS spectral signal is detected using an Echelle spectrometer + iCCD camera, which provides the whole time-resolved NUV-NIR spectrum in a single laser shot. 

Figure I. Schematic layout of an echelle grating waveguide spectrometer.

Another approach was attempted by Seppala and Kylma who reported the synthesis of poly(ester-urethane)s by condensation of hydroxyl terminated tel-echelic poly(CL-co-LA) oligomers with 1,6-hexamethylene diisocyanate (Scheme 33) [94]. The diisocyanate acts as chain extender producing an increase in molecular weight of the preformed oligomers. The authors claim that some of the copolymers present elastomeric properties. Using a similar method. Storey described the synthesis of polyurethane networks based on D,L-LA, GA, eCL,... 

The VLT, centrepiece of the ESO, promises an exceptional harvest of astronomical data. Understanding the chemical evolution of the Universe requires a coordinated study of the most remote objects, ancient stars in the galactic halo and absorbent clouds in the line of sight of quasars. To this end, the high-resolution spectrograph UVES (Ultraviolet Echelle Spectrograph) was set at one focus of Kueyen, one of the four components of the VLT, perched at the top... 

The final point to consider is the matter of the physical mode of the metaphorical descent by Duchamp s nude, which is by means of un escaUer. This is the same word used in French for either stairs or a staircase, and it has its root in the Latin scala, scalae, meaning either stairs or ladder. A ladder in French is an echelle, derived from ichehn (step) accordingly, Poisson cites... 

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