DRAMIŃSKI - Nir spectroscopy

DRAMIŃSKI NIR-DRAM 100 - Near Infra Red Analyser of grain and flour content
The analyser is an advanced hi-tech device for measuring grain & flour composition by spectral analysis in the near-infrared spectral range.

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By comparing data taken in 2003 [18] with earlier measurements in 1999 [15] we can set an upper limit on the variation of the 1S-2S transition frequency of (-29 ± 57) Hz within 44 months. To derive limits on the drift rates of fundamental constant such as the fine structure constant, we combine these measurements with other optical frequency measurements in Hg+ and in Yb+ performed at NIST, Boulder/USA [19] and at PTB, Braunschweig/Germany [20] respectively. This combined method gives precise and separate restrictions for the fractional time variation of the fine structure constant and the Cs nuclear magnetic moment measured in Bohr magnetons. The latter is a measure of the drift rate of the strong interaction.

According to the Schrödinger theory 2 times the 2S-4S transition frequency should be half of the 1S-2S transition frequency. By longitudinal Doppler-free two-photon excitation of a cold hydrogen beam we have observed the beat frequency between the frequency doubled IR radiation, used to drive the 2S-4S transition, and the blue light used to drive the 1S-2S transition after being frequency doubled. If the well-known fine and hyperfine structure and the first order correction of the Dirac energies due to the finite nuclear mass is subtracted, this beat contains a combination of Lamb shifts of the involved levels. On the other hand, if one believes in QED, a more accurate value of the proton charge radius can be extracted from those frequencies.

The 486 nm radiation of the dye laser is transfered through an optical fiber to the frequency comb [17] to compare it phase-coherently with a Cs atomic clock. In this way the absolute frequency of the hydrogen 1S-2S transition is determined with one of the most precise measurement tools. Subtracting the Lamb shift from the measured frequency a value for Rydberg may be derived from the remainder. On the other hand if one uses a value for the for Rydberg constant determined in a different experiment and a measured for the 2S Lamb shift [8] a value of the 1S Lamb shift may be derived. This is an important result since the Lamb shift of the 1S level is the largest of all hydrogen energy levels and it is not accessible to radio frequency methods. The most general way to determine the constants given above is to use not only the 1S-2S transition frequency but all available hydrogen data [16].

In the 1S-2S experiment hydrogen atoms are excited by longitudinal Doppler-free two photon excitation at 243 nm. This radiation is generated by a frequency doubled ultrastable dye laser at 486 nm. The UV radiation is then resonantly enhanced in a linear cavity inside a vacuum chamber . Atomic hydrogen from a gas discharge is directed through a nozzle cooled with liquid helium. The cold atomic beam is oriented along the axis of the enhancement resonator. After the atoms have passed a distance L, usually around 10 cm, a small electric field that mixes the metastable 2S state (lifetime 1/7 sec) with the fast decaying 2P state is applied. To reduce the residual second order Doppler-effect we use a delayed detection scheme where the fluorescence at 121 nm is detected only after the exciting light has been switched off for a period T, typically between 0.5 and 1.8 ms. In this way we set an upper limit on the second order Doppler-shift below 1 kHz.

For many years high resolution spectroscopy on atomic hydrogen has been essential for the development and testing of fundamental theories. Today the precise determination of transition frequencies and relations among them provides one of the most rigorous verification of QED [1,2,3]. The most precise values of the Rydberg constant to date are derived from optical frequency measurements in atomic hydrogen [4,5]. From the comparison of the transition frequencies in hydrogen and deuterium the deuteron structure radius can be extracted. Since the deuteron is the simplest nucleus (besides the proton) knowledge about its structure is essential to test nuclear models [6]. A survey of recent developments in high resolution hydrogen spectroscopy and its theoretical treatment is presented in [7].

f(1S-2S) = 2 466 061 102 474 851(34) Hz

R = 10 973 731.568 525(84) m-1

L1S = 8 172.840(22) MHz

AA spectrometers use monochromators and detectors for uv and visible light. The main purpose of the monochromator is to isolate the absorption line from background light due to interferences. Simple dedicated AA instruments often replace the monochromator with a bandpass interference filter. Photomultiplier tubes are the most common detectors for AA spectroscopy.

AA spectroscopy requires that the analyte atoms be in the gas phase. Ions or atoms in a sample must undergo desolvation and vaporization in a high-temperature source such as a flame or graphite furnace. Flame AA can only analyze solutions, while graphite furnace AA can accept solutions, slurries, or solid samples.

Flame AA uses a slot type burner to increase the path length, and therefore to increase the total absorbance (see Beer-Lambert law). Sample solutions are usually aspirated with the gas flow into a nebulizing/mixing chamber to form small droplets before entering the flame.

The graphite furnace has several advantages over a flame. It is a much more efficient atomizer than a flame and it can directly accept very small absolute quantities of sample. It also provides a reducing environment for easily oxidized elements. Samples are placed directly in the graphite furnace and the furnace is electrically heated in several steps to dry the sample, ash organic matter, and vaporize the analyte atoms.