Browsing by Author "Ikonen, Erkki, Prof."

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  • Advanced applications of wavelength tunable lasers in metrology and fundamental physics
    (2010) Ahtee, Ville
     Elektroniikan, tietoliikenteen ja automaation tiedekunta | Doctoral dissertation (article-based)
    In this thesis, measurement systems based on wavelength tunable lasers have been developed and studied to improve measurement capabilities in the fields of optical metrology and quantum optics. In the first work presented in this thesis, techniques for precision measurements of absolute spectral irradiance responsivity of detectors were investigated. Two laser-based methods and a traditional monochromator based method were compared in the near infrared wavelength region. The results between absolute responsivity measurements using the three different measurement systems demonstrated agreement at the uncertainty level of less than 0.1 % (k = 1). The second work consists of an acetylene-stabilized laser and an optical single-frequency synthesizer that were constructed and characterized for precision optical frequency measurements at telecommunication wavelengths. The acetylene-stabilized laser was designed by taking a fiber-based approach, which enabled a relatively straightforward implementation of the optical set-up. The frequency of the stabilized-laser was measured absolutely using an optical frequency comb generator. The results agree well with the recommendation by the International Committee for Weights and Measures (CIPM). The single-frequency synthesizer was designed for generating a single user-specified frequency from an atomic time base within the 192-196 THz gain bandwidth of an erbium-doped fiber amplifier (EDFA). The synthesizer was utilized for studying spectral lineshapes of acetylene transitions near 1540 nm. The recorded spectra were investigated by theoretical fits and the obtained line-center frequencies were compared to line-center frequencies measured with the acetylene-stabilized laser using the third harmonic technique. The results agreed well with each other. Final part of the thesis describes a set-up that is capable of emitting indistinguishable single photons using single molecules as photon sources. This was achieved by combining high resolution laser spectroscopy and optical microscopy at cryogenic conditions. Two single molecules in separate microscopes were identified and DC-Stark effect was exploited to shift the resonance frequencies of given molecules for perfect spectral overlap. Excitation by pulsed laser enabled triggered generation of identical single photons from two independent single molecules. The results can be utilized in the development of a number of different quantum information processing schemes.
  • Applied diode laser spectroscopy and characterization of optical fiber nonlinearity
    (2011) Hieta, Tuomas
     School of Electrical Engineering | Doctoral dissertation (article-based)
    This thesis describes work and progress on accurate nonlinearity measurements of optical fibers, design and characterization of external cavity diode lasers, and spectroscopic measurement of air temperature and humidity for accurate determination of the refractive index of air. The first part of the thesis describes measurement of the nonlinear coefficient of standard and erbium-doped single-mode fibers, commonly used in telecommunications. A simulation tool was developed to model the previously neglected effects of dispersion in the continuous-wave self-phase modulation method. The simulation can be included in already existing measurement set-ups increasing their versatility and reducing their uncertainty. It is shown that reliable erbium-doped fiber nonlinearity measurements are possible even for very short fibers when the whole measurement system is carefully characterized for nonlinearity. With the help of the dispersion simulation and a carefully optimized fiber optic power measurement, an expanded uncertainty of 2.0 % (k =2) was achieved for the nonlinearity of a single-mode fiber. The Expanded uncertainty for measurement of an erbium-doped fiber was found to be 3.0 % (k =2). Applied diode laser spectroscopy is covered in the second part of this thesis. External-cavity diode laser based on non-dispersive holographic volume grating was designed and characterized in this work. The use of a non-dispersive element for feedback eliminates beam directional variations and enables compact design with good wavelength reproducibility. Laser designs for applications in metrology, molecular spectroscopy and for multicomponent absorption spectroscopy were developed. This thesis describes accurate measurement of temperature and humidity using diode laser spectroscopy, which is crucial for refractive index compensation in demanding interferometric length measurements. The measurement system was tested both in laboratory and outdoor environment successfully over distances up to 130 m. The standard deviation of temperature measurement in laboratory environment was 7 mK using a 120 s sample time, which is the best spectroscopic value ever reported. Performance of the system was found to be excellent when a commercial interferometer was compensated in an environment with local temperature variations, demonstrating the suitability of the method for industrial dimensional measurements. A portable and robust temperature measurement set-up was developed for long-distance geodetic applications. The set-up was tested successfully in harsh outdoor conditions.
  • Spectral irradiance and radiation temperature scales
    (2010) Ojanen, Maija
     Aalto-yliopiston teknillinen korkeakoulu | Doctoral dissertation (article-based)
    Spectral irradiance and radiation temperature measurements are needed in various applications, from environmental studies to different fields of industry. Scale realizations are needed to serve the calibration needs of these applications. In this thesis, I present various improvements to the scales of spectral irradiance and radiation temperature. A physical model was developed for tungsten halogen lamps utilized as spectral irradiance sources. The model consists of Planck's radiation law, emissivity of tungsten in polynomial form, and a correction function. The model can interpolate the spectral irradiance values of lamps with an agreement better than 1 % with previous calibrations by MIKES/TKK and NPL (UK) throughout the spectral region 340 nm - 850 nm. Spectral irradiance scales of MIKES/TKK and NMC (Singapore) were compared using an automated multi-wavelength filter radiometer. The wavelength range of the comparison was 290 nm - 900 nm. The agreement was compared with the results of the previous key comparison. The results indicated that the long-term reproducibility of the spectral irradiance scale of MIKES is excellent in the wavelength range above 400 nm. In the range 290 nm - 400 nm, the reproducibility is within 2.8 %, which is still within the expanded uncertainties of the comparison. The spectral irradiance scale of NIMT (Thailand) was linked to the CIPM key comparison reference value using MIKES as a link in a bilateral key comparison. I present a method for uncertainty estimation in linking key comparisons. A detector-based radiation temperature scale was developed at MIKES. Filter radiometers were first compared with a Ag fixed point cell, and then with a linear pyrometer in the temperature range of 1370 K - 1770 K. With help of the filter radiometers, the extrapolation of the pyrometer readings could be studied. The radiation temperature scales of MIKES and PTB (Germany) were compared in the range 1570 K - 2770 K. Both the International Temperature Scale of 1990 (ITS-90) and thermodynamic temperature scales were compared. The ITS-90 based scales were in agreement. The agreement of the thermodynamic temperature scales was partial: The results for two out of four filter radiometers of MIKES agreed with each other and with those of PTB, whereas the results from the two others showed deviations. Possible reasons for this deviation, such as differences in measurement geometries and possible diffuse transmittance in the interference filters, are postulated and discussed.
  • Spectrally Adjustable Radiance Source
    (2013) Hirvonen, Juha-Matti
     School of Electrical Engineering | Licentiate thesis
    A spectrally adjustable radiance source based on light emitting diodes (LEDs) has been constructed for spectral responsivity measurements of radiance and luminance meters. A 300-mm integrating sphere source with adjustable output port is illuminated using 30 thermally stabilized narrow-band LEDs covering the visible wavelength range of 380–780 nm. The functionality of the measurement setup is demonstrated by measuring the relative spectral responsivities of a luminance meter and a photometer head with cosine-corrected input optics.