| 1. |
- Askebjer, P., et al.
(författare)
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Optical properties of deep ice at the South Pole : Absorption
- 1997
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Ingår i: Applied Optics. - : Optical Society of America. - 0003-6935 .- 1539-4522. ; 36:18, s. 4168-4180
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Tidskriftsartikel (refereegranskat)abstract
- We discuss recent measurements of the wavelength-dependent absorption coefficients in deep South Pole ice. The method uses transit-time distributions of pulses from a variable-frequency laser sent between emitters and receivers embedded in the ice. At depths of 800-1000 m scattering is dominated by residual air bubbles, whereas absorption occurs both in ice itself and in insoluble impurities. The absorption coefficient increases approximately exponentially with wavelength in the measured interval 410-610 nm. At the shortest wavelength our value is approximately a factor 20 below previous values obtained for laboratory ice and lake ice; with increasing wavelength the discrepancy with previous measurements decreases. At ∼415 to ∼500 nm the experimental uncertainties are small enough for us to resolve an extrinsic contribution to absorption in ice: submicrometer dust particles contribute by an amount that increases with depth and corresponds well with the expected increase seen near the Last Glacial Maximum in Vostok and Dome C ice cores. The laser pulse method allows remote mapping of gross structure in dust concentration as a function of depth in glacial ice.
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| 2. |
- Askebjer, P, et al.
(författare)
-
Optical properties of deep ice at the South Pole: Absorption
- 1997
-
Ingår i: APPLIED OPTICS. - : OPTICAL SOC AMER. - 0003-6935. ; 36:18, s. 4168-4180
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We discuss recent measurements of the wavelength-dependent absorption coefficients in deep South Pole ice. The method uses transit-time distributions of pulses from a variable-frequency laser sent between emitters and receivers embedded in the ice. At dep
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| 3. |
- Carlsson, Torgny E., et al.
(författare)
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Method for fringe enhancement in holographic interferometry for measurement of in-plane displacements
- 1998
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Ingår i: Applied Optics. - : Optical Society of America. - 0003-6935 .- 1539-4522. ; 37:10, s. 1845-1848
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Tidskriftsartikel (refereegranskat)abstract
- Theoretical background along with experimental results are given for a simple method for in-plane fringe enhancement in dual-beam illumination holographic interferometry. In this method, the fringes representing in-plane displacements arise as a moirépattern between two interferograms. To distinguish the in-plane displacement, a sequence of images is recorded while the reference mirror is continuously tilted at random. The in-plane fringes arethen found as the maximum contrast of the out-of-plane fringes in the image sequence. The resulting fringe quality is close to the quality of the out-of-plane fringes.
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| 4. |
- Fällman, Erik, et al.
(författare)
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Design for fully steerable dual-trap optical tweezers
- 1997
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Ingår i: Applied Optics. - : Optical Society of America. - 0003-6935 .- 1539-4522. ; 36:10, s. 2107-2113
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Tidskriftsartikel (refereegranskat)abstract
- A design for complete beam steering (in three dimensions) of one or two optical tweezers traps is presented. The two most important requirements for efficient and stable movement of an optical trap are identified. A detailed recipe for the construction of a movable optical tweezers trap that fulfills these requirements is given (exemplified with an inverted microscope). The system has been found to allow for precise and free movements of both traps in all three dimensions in a dual-trap optical tweezers configuration and to be robust and reliable, as well as forgiving of small misalignments in the optical system.
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| 5. |
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| 6. |
- Karmhag, R, et al.
(författare)
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TiN-alloy coatings for temperature control of space vessels
- 1999
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Ingår i: APPLIED OPTICS. - : OPTICAL SOC AMER. - 0003-6935. ; 38:4, s. 674-678
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Tidskriftsartikel (refereegranskat)abstract
- The problem of combining the temperature control of a space vehicle with the mechanical and chemical stability of the surface is addressed. With the absorption of solar radiation and the emission of thermal radiation considered the static and dominant fac
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| 7. |
- Kluczynski, Pawel, et al.
(författare)
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Theoretical description based on Fourier analysis of wavelength-modulation spectrometry in terms of analytical and background signals
- 1999
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Ingår i: Applied Optics. - : Optical Society of America. - 0003-6935 .- 1539-4522. ; 38:27, s. 5803-5815
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Tidskriftsartikel (refereegranskat)abstract
- A theoretical description of the wavelength-modulation (WM) spectrometry technique is given. The formalism is based on Fourier analysis and can therefore correctly handle arbitrary large frequency-modulation amplitudes. It can also deal with associated intensity modulations as well as wavelength-dependent transmission effects. It elucidates clearly how various Fourier components of these entities combine with those of the line-shape function to yield separately the final analytical and background nf WM signals. Explicit expressions are given for the 2f and the 4f signals. It is shown, among other things, that the 4f technique in general gives rise to smaller background signals (and therefore larger signal-to-background ratios) than does the 2f technique when the background is dominated by etalon effects from short cavities and that a finite intensity modulation necessarily leads to an out-of-phase nf WM signal. The formalism is also able to elucidate clearly that a linear intensity modulation is not sufficient to cause any 2f background residual-amplitude-modulation signals (as was the general consensus until recently in the literature) but that 2f background signals instead can exist only in systems with either wavelength-dependent transmission or a laser with nonlinear intensity modulation.
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| 8. |
- Ljungberg, Peter, et al.
(författare)
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Degenerate four-wave mixing from laser-populated excited states
- 1995
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Ingår i: Applied Optics. - : Optical Society of America. - 0003-6935 .- 1539-4522. ; 34:3, s. 527-536
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Tidskriftsartikel (refereegranskat)abstract
- Degenerate four-wave mixing (DFWM) from laser-populated excited states, i.e., two-step DFWM (2S-DFWM), has been performed to investigate the possibility of increasing signal quality (i.e., strength or signal-to-noise ratio) when species with low transition probabilities or far-UV transitions are to be detected or when large beam areas are used. Gold atoms, aspirated into an air-acetylene flame, were chosen as a suitable species for this investigation. The 2S-DFWM signal strength was found to be comparable to the ordinary (one-step) DFWM signals for moderately high UV-light intensities but substantially better for low UV-light intensities. This finding implies that DFWM detection of species with lower transition probabilities in the first step as compared with gold (< 10-8 s-1) can benefit from the 2S-DFWM technique when moderate or low UV-light intensities are available. Additional possible advantages of using 2S-DFWM are also discussed.
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| 10. |
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