Browsing by Author "Hildén, Panu"

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  • Continuous wave Bessel beams with a strong longitudinal acceleration in free space
    (2022-08-15) Ilina, Elena; Hildén, Panu; Kaivola, Matti; Shevchenko, Andriy
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    A variety of transversely accelerating optical beams, such as Airy, Mathieu, and Weber beams, have been proposed and intensively studied in the past few decades, while longitudinal acceleration of optical beams in free space has been considered much less and mostly for ultrashort optical pulses. In this work, we create two-component continuous wave Bessel beams that exhibit extremely high longitudinal acceleration in free space, with the group velocity changing by a factor of 10 in just a few centimeters of propagation. The beam components are co-propagating interfering optical beams that can have different frequencies and angular spectra. We also demonstrate large-magnitude negative group velocities and zero-group-velocity modes for a two-component beam. The group velocities are measured interferometrically, using a common-path optical interferometer. The measurement results agree well with the theoretical predictions. The presented methods to control and measure the group velocity of light in free space are expected to attract the attention of researchers working on optical interferometry, ultrafast optics, nonlinear optics, and optical tweezers.
  • Differenttiaalinen optinen absorptiospektroskopia
    (2016-12-20) Hildén, Panu
     Sähkötekniikan korkeakoulu | Bachelor's thesis
  • Laser light source for photoacoustic spectroscopy of hydrogen chloride
    (2019-08-19) Hildén, Panu
     Sähkötekniikan korkeakoulu | Master's thesis
    Continuous reduction in the size of integrated circuits has made circuit components vulnerable to small doses of airborne molecular contaminants (AMCs), such as hydrogen chloride (HCl), present in a cleanroom environment. The contamination reduces yields of manufacturing processes making them less cost effective. Monitoring of the AMCs can help to control contamination, and thus improve the yields. For this thesis, an optically amplified laser light source for spectroscopic monitoring of HCl was built and tested. In order to detect absorption peaks of the HCl, the laser source operates at a spectral band around a wavelength of 1740 nm. Laser diodes operating at the spectral band can output only low power signals, which limits the detection level of HCl in photoacoustic spectroscopic (PAS) measurements, where the generated signal is proportional to the amount of absorbed light. The laser source built for the thesis, improves the detection limit by amplifying the power of the optical signal generated by the laser diode. The amplification process is based on bismuth-doped fiber (BDF), which is pumped with energy using high power laser diodes. For the design of laser amplifier pumping scheme, gain of the bismuth-doped fiber amplifier (BDFA) was simulated using MATLAB. The simulation results were then compared with corresponding measurements in order to evaluate the simulation. For the control of the laser diodes used in the laser amplifier, LabVIEW program was written. The program controls the temperatures and injection currents of the laser diodes via DAQ devices and laser diode drivers. The program can be used to modulate laser diode injection currents, so that the laser source can be used for wavelength modulation photoacoustic spectroscopy (WM-PAS). Finally, the laser source was used to measure the HCl concentrations of calibration gases.
  • Matrix analysis of high-density arrayed waveguides : Crosstalk suppression by bending
    (2024-08) Hildén, Panu; Shevchenko, Andriy
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    For many photonic devices, crosstalk between densely packed waveguides poses a major problem leading to unreliable or inefficient operation of the device. In this work, a general method for modeling the crosstalk, not only in straight waveguide arrays but also in curved ones, is introduced. The method is based on a matrix analysis of electromagnetic field coupling between closely spaced waveguides. As an example, we show how bending of waveguides in an array reduces the crosstalk. The approach can help overcome the crosstalk problem in a variety of photonic integrated devices, including phased waveguide arrays, arrayed waveguide gratings, optical multiplexers, and high-density interconnects between optical and electronic components.
  • Prism-based approach to create intensity-interferometric non-diffractive cw light sheets
    (2022-07-04) Hildén, Panu; Kaivola, Matti; Shevchenko, Andriy
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Light sheets are optical beam-like fields with one-dimensional intensity localization. Ideally, the field intensity should be independent of the longitudinal and one of the transverse coordinates, which is difficult to achieve even for truncated light sheets. In this work, we present a general theoretical framework for intensity-interferometric continuous wave (cw) light sheets formed by overlapping the interference fringe patterns of mutually uncorrelated frequency components of the field. We show that the key parameters of the light sheets can be calculated using simple analytical expressions. We propose a practical way to generate such light sheets with the help of prisms and demonstrate numerically the abilities of the method. Both bright and dark light sheets with an exceptionally small thickness and long divergence-free propagation distance are possible to generate. We also show that the transverse profile of the generated light sheets can be shaped by modifying the spectrum of the light. We believe our findings advance the beam-engineering technology and its applications.