Flip mirror

Fig. 6.8. A Principle of frequency-multiplexed CARS microspectroscopy A narrow-bandwidth pump pulse determines the inherent spectral resolution, while a broad-bandwidth Stokes pulse allows simultaneous detection over a wide range of Raman shifts. The multiplex CARS spectra shown originate from a 70 mM solution of cholesterol in CCI4 (solid line) and the nonresonant background of coverglass (dashed line) at a Raman shift centered at 2900 cm-1. B Energy level diagram for a multiplex CARS process. C Schematic of the multiplex CARS microscope (P polarizer HWP/QWP half/quarter-wave plate BC dichroic beam combiner Obj objective lens F filter A analyzer FM flip mirror L lens D detector S sample). D Measured normalized CARS spectrum of the cholesterol solution. E Maximum entropy method (MEM) phase spectrum (solid line) retrieved from (D) and the error background phase (dashed line) determined by a polynomial fit to those spectral regions without vibrational resonances. F Retrieved Raman response (solid line) calculated from the spectra shown in (E), directly reproducing the independently measured spontaneous Raman response (dashed line) of the same cholesterol sample...

A flip mirror (not shown) allows the sample to be viewed through a 10 X ocular and brought into focus. The optical elements of this accessory have been aligned so that the visible focus is coincident with the focus of IR radiation. 

FT-IR spectrometers cannot be built as double-beam instruments. Unlike dispersive instruments, FT-IR spectrometers acquire single channel spectra of sample and reference and their ratio is calculated afterwards (Fig. 4.2). Sample and reference may automatically be replaced by a sample slider, or the IR beam may be switched between sample and reference by flip-mirrors. In the case of higher accumulation numbers, the instrument switches repeatedly between sample and reference scan. 

Traditionally, FT-IR spectrometers used to be divided into two groups, routine and research spectrometers. Both have an affiliated PC for the data processing and handling. Routine spectrometers usually have a resolution limit of ca. 1 cm. Research spectrometers can achieve resolution as high as 0.001 cm . Sources, beamsplitters and detectors are exchangeable in research spectrometers, so one could use these spectrometers from 40000 down to 20 cm (from the UV to far-IR range). In some spectrometers different sources and detectors are installed permanently. They can be switched on or off by means of flip mirrors. Nowadays there are no designated limits between routine and research instraments. 

Many FT-IR spectrometers have external ports for optical coupling to dedicated accessories. The IR radiation is conveniently directed to/from the external ports by computer-controlled flip mirrors. A large variety of accessories, like an IR microscope, interfaces for gas chromatography (GC/FT-IR), liquid chromatography (HPLC/FT-IR), thin layer chromatography FT-IR (TLC/FT-IR), etc., is commercially available. This type of method combination is usually called a hyphenated technique. FTIR spectrometers can even be supplemented by a FT-Raman accessory. The versatile combination of FT-IR spectrometers with other instruments has substantially contributed to their abundance in most analytical laboratories. 

Figure 6.8. Optics of the Nicolet Model 60-SX FT-IR spectrometer (now obsolete). Sources can be located at Si, S2, and/or S3 detectors can be located at Di, D2, and/or D3 M signifies a fixed mirror MF signifies a flip mirror Ai is a Jacquinot stop.

Some sampling accessories [e.g., infrared microscopes (see Chapter 14) and gas chromatography interfaces (see Chapter 23)] are too big to fit in even the largest sample compartment. In these cases, the accessories are mounted outside the instrument and the modulated beam is directed to them by means of a switch-able mirror (often known as di flip mirror). It is very rare that the beam is returned to the detector mounted inside the instrument, so a second detector is usually a component of accessories that are mounted outside the spectrometer in the external beam. Several contemporary instruments are also equipped with flip mirrors to direct the beam to different possible internal beam paths, in one or more of which a different accessory may be mounted permanently. In this way, the user can switch rapidly from one type of measurement to another, making optimal use of a single spectrometer. 

C chopper FM flipping mirror OPA optical parametric amplifier WLG white light generator, SFIG-TFIG second harmonic and third harmonic generators... 

Ring inversion (Section 3 9) Process by which a chair conforma tion of cyclohexane is converted to a mirror image chair All of the equatonal substituents become axial and vice versa Also called ring flipping or chair-chair interconversion... 

Figure 3.6 Structure 1 is a molecule that has been shown experimentally to be optically inactive, but which is dissymetric. In step (a) it is reflected in a vertical mirror perpendicular to the plane of the paper. In step (b) the mirror image 2 is flipped vertically and rotated to make the bottom half of 3 coincide with the bottom half of 1.

We can draw two nonsuperimposable mirror images of the most stable chair conformation of trans-1,2-dibromocyclohexane with both bromines equatorial. These structures cannot interconvert by ring-flips or other rotations about bonds, however. They are mirror-image isomers enantiomers. 

The laser beam from each head is collected and focussed by an off-axis parabolic mirror, OAP, or 0APa and then directed to a selection mirror, S which flips back and forth to permit the beam from each of the diodes to enter the White cell in turn. 

One can say that the mirror folds the length axis at the mirror, so that emergent rays to a real image at the left represent a positive value of s. We are forced also to declare that the mirror also flips the sign of the surface radius. For reflective surfaces, the radius of curvature is defined to be the directed distance from a surface to its center of curvature, measured with respect to the axis used for the emergent light. With this qualification the convention for the signs of s and R is the same for mirrors as for refractive surfaces. 

In the chemical sector, the received wisdom is that in their relendess focus on making money, LBO practitioners resort to slash and bum tactics, compromising environmental health and safety. They are sometimes referred to as the bottom fishers looking for a quick flip . In addition, they are often described as financial magicians who turn solid balance sheets into smoke and mirrors. 

Five-membered rings typically have non-planar conformers, either a puckered C2 envelope or a Q half chair (Figure 14). The conformers are readily intercon-verted by flipping one CH2 from above the approximate ring plane to below. Ring inversion converts the molecule into its mirror image, interchanging equatorial and... 

After you ve drawn something, press F. Instantly, the sprite is flipped upside down. Press it again to flip it back over. Remember F as the command for Flip. Now try M, for Mirror. The shape you ve drawn is mirrored left to right. Of course, if you ve drawn something symmetrical, you may not see any change. 

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