| 1. |
- Amer, Eynas, et al.
(författare)
-
Comparison of the laser ablation process on Zn and Ti using pulsed digital holographic interferometry
- 2010
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 256:14, s. 4633-4641
-
Tidskriftsartikel (refereegranskat)abstract
- Pulsed digital holographic interferometry has been used to compare the laser ablation process of a Q-switched Nd-YAG laser pulse (wavelength 1064 nm, pulse duration 12 ns) on two different metals (Zn and Ti) under atmospheric air pressure. Digital holograms were recorded for different time delays using collimated laser light (532 nm) passed through the volume along the target. Numerical data of the integrated refractive index field were calculated and presented as phase maps. Intensity maps were calculated from the recorded digital holograms and are used to calculate the attenuation of the probing laser beam by the ablated plume. The different structures of the plume, namely streaks normal to the surface for Zn in contrast to absorbing regions for Ti, indicates that different mechanisms of laser ablation could happen for different metals for the same laser settings and surrounding gas. At a laser fluence of 5 J/cm2, phase explosion appears to be the ablation mechanism in case of Zn, while for Ti normal vaporisation seems to be the dominant mechanism.
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| 2. |
- Amer, Eynas, et al.
(författare)
-
Evaluation of Shock Tube Retrofitted with Fast-Opening Valve for Dynamic Pressure Calibration
- 2021
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Ingår i: Sensors. - : MDPI. - 1424-8220. ; 21:13
-
Tidskriftsartikel (refereegranskat)abstract
- Accurate dynamic pressure measurements are increasingly important. While traceability is lacking, several National Metrology Institutes (NMIs) and calibration laboratories are currently establishing calibration capacities. Shock tubes generating pressure steps with rise times below 1 µs are highly suitable as standards for dynamic pressures in gas. In this work, we present the results from applying a fast-opening valve (FOV) to a shock tube designed for dynamic pressure measurements. We compare the performance of the shock tube when operated with conventional single and double diaphragms and when operated using an FOV. Different aspects are addressed: shock-wave formation, repeatability in amplitude of the realized pressure steps, the assessment of the required driver pressure for realizing nominal pressure steps, and economy. The results show that using the FOV has many advantages compared to the diaphragm: better repeatability, eight times faster to operate, and enables automation of the test sequences.
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| 3. |
- Amer, Eynas, et al.
(författare)
-
Impact of an extended source in laser ablation using pulsed digital holographic interferometry and modelling
- 2009
-
Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 255:21, s. 8917-8925
-
Tidskriftsartikel (refereegranskat)abstract
- Pulsed digital holographic interferometry has been used to study the effect of the laser spot diameter on the shock wave generated in the ablation process of an Nd:YAG laser pulse on a Zn target under atmospheric pressure. For different laser spot diameters and time delays, the propagation of the expanding vapour and of the shock wave were recorded by intensity maps calculated using the recorded digital holograms. From the latter phase maps, the refractive index and the density field can be derived. A model was developed that approaches the density distribution, in particular the ellipsoidal expansion characteristics. The induced shock wave has an ellipsoid shape that approaches a sphere for decreasing spot diameter. The ellipsoidal shock waves have almost the same centre offset towards the laser beam and the same aspect ratio for different time steps. The model facilitates the derivation of the particle velocity field. The method provides valuable quantitative results that are discussed, in particular in comparison with the simpler point source explosion theory.
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| 4. |
- Amer, Eynas, et al.
(författare)
-
Laser-ablation-induced refractive index fields studied using pulsed digital holographic interferometry
- 2009
-
Ingår i: Optics and lasers in engineering. - : Elsevier BV. - 0143-8166 .- 1873-0302. ; 47:7-8, s. 793-799
-
Tidskriftsartikel (refereegranskat)abstract
- Pulsed digital holographic interferometry has been used to investigate the plume and the shock wave generated in the ablation process of a Q-switched Nd-YAG (λ=1064 nm and pulse duration=12 ns) laser pulse on a polycrystalline boron nitride (PCBN) target under atmospheric air pressure. A special setup based on two synchronised wavelengths from the same laser for simultaneous processing and measurement has been used. Digital holograms were recorded for different time delays using collimated laser light (λ=532 nm) passed through the volume along the target. Numerical data of the integrated refractive index field were calculated and presented as phase maps showing the propagation of the shock wave and the plume generated by the process. Radon inversion has been used to estimate the 3D refractive index fields measured from the projections assuming rotational symmetry. The shock wave density has been calculated using the point explosion model and the shock wave condition equation and its behaviour with time at different power densities ranging from 1.4 to 9.1 GW/cm2 is presented. Shock front densities have been calculated from the reconstructed refractive index fields using the Gladstone-Dale equation. A comparison of the shock front density calculated from the reconstructed data and that calculated using the point explosion model at different time delays has been done. The comparison shows quite good agreement between the model and the experimental data. Finally the reconstructed refractive index field has been used to estimate the electron number density distribution within the laser-induced plasma. The electron number density behaviour with distance from the target at different power densities and its behaviour with time are shown. The electron number densities are found to be in the order of 1018 cm-3 and decay at a rate of 3×1015 electrons/cm3 ns.
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| 5. |
- Amer, Eynas, et al.
(författare)
-
Measurement of selective species concentration using spectroscopic holography
- 2018
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Ingår i: Speckle 2018. - : SPIE - International Society for Optical Engineering. - 9781510622975
-
Konferensbidrag (refereegranskat)abstract
- Spectroscopic holography refers to techniques in which the detected hologram contains information about specific species in the medium under study. In general, at least two lasers are required with wavelengths chosen carefully to fit the interaction process utilized. In this process, energy from the shorter wavelength laser beam is transferred to the longer wavelength coherently through the process of stimulated emission. Two interaction mechanisms are considered; Stimulated Laser Induced Fluorescence (LIF) and Stimulated Raman Scattering (SRS), which both are species specific with the ability of coherent interaction. In this paper, the fundamental properties of spectroscopic holography is presented and demonstrated with a few idealized experiments. These validation experiments are performed in a gas chamber in which different gases may be blended and the gas pressure changed between 1-12 bars. In addition, two examples of applications are presented. In the first set of experiments, LIF holography is used to image light absorption and laser heating in a dye simultaneously. The second set of experiments is performed in a ow of methane gas. It is demonstrated that the combination of holographic phase measurements and SRS gain images may be used for calibration. This calibration may further be used to measure absolute concentration in a burning flame.
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| 6. |
- Amer, Eynas
(författare)
-
Pulsed laser ablation studied using digital holographic interferometry
- 2008
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Pulsed digital holographic interferometry has been used to investigate the plume and the shock wave generated in the ablation process of a Q-switched Nd-YAG (lambda= 1064 nm and pulse duration = 12 ns) laser pulse on a polycrystalline Boron Nitride (PCBN) target under atmospheric air pressure. A special set-up based on using two synchronised wavelengths from the same laser for simultaneous processing and measurement has been used. Digital holograms were recorded for different time delays using collimated laser light (lambda= 532 nm) passed through the volume along the target. Numerical data of the integrated refractive index field were calculated and presented as phase maps showing the propagation of the shock wave and the plume generated by the process. Radon inversion has been used to estimate the 3D refractive index fields measured from the projections assuming rotational symmetry. Verification of the point explosion model has been done. The amount of released energy i.e. the part of the incident energy of the laser pulse that is eventually converted to a shock wave has been estimated. Shock wave front densities have been calculated from the reconstructed refractive index fields using the Gladstone-Dale equation. A comparison of the shock front density calculated from the reconstructed data and that calculated using the point explosion model at different time delays has been done. The comparison shows quite good agreement between the model and the experimental data. Finally the reconstructed refractive index field has been used to estimate the electron number density distribution within the laser induced plasma. The results show that pulsed digital holographic interferometry is a promising technique to study laser ablation processes. Different materials and laser parameters like wavelength, focusing, number of pulses can be studied in combinations with other techniques.
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| 7. |
|
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| 8. |
- Amer, Eynas
(författare)
-
Pulsed laser ablation studied using digital holography
- 2009
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Pulsed digital holographic interferometry has been used to study the plume and the shock wave generated in the laser ablation process on different targets under atmospheric air pressure. A pulsed Nd-YAG laser system (pulse duration 12 ns) has been used both for ablating the material (wavelength 1064 nm) and for measurement (wavelength 532 nm). Digital holograms were recorded for different time delays using collimated laser light passed through the volume along the target. Numerical data of the integrated refractive index field were calculated and presented as phase maps. The Radon inversion has been used to estimate the 3D refractive index fields measured from the projections assuming rotational symmetry. Intensity maps have been calculated from the recorded digital holograms and used to calculate the attenuation of the probing laser beam by the ablated plume. Qualitative and quantitative information have been extracted from both the phase map and the intensity map to help describing the laser ablation process. Also 3D information about the induced plume has been obtained by numerical reconstruction of the digital holograms at different planes along the plume. The amount of released energy due to laser impact on a PCBM target has been estimated using the point explosion model. The released energy is normalized by the incident laser pulse energy and the energy conversion efficiency between the laser pulse and the target has been calculated and it seems to be constant around 80 %. The 3D refractive index fields have been used to calculate the shock wave front density and the electron number density distribution within the induced plasma. The electron number densities are found to be in the order of 1018 cm-3 and decay at a rate of 3x1015 electrons/cm3ns. The effect of the laser spot diameter on the shock wave generated in the ablation process of a Zn target has been studied. The induced shock wave has an ellipsoidal shape that approaches a sphere for decreasing spot diameter. A model was developed that approaches the density distribution that facilitates the derivation of the particle velocity field. The method provides quantitative results that are discussed; in particular a comparison with the point explosion theory. The effect of the physical properties of the target on the laser ablation process has been studied. The comparison of the laser ablation of Zn and Ti shows that different laser ablation mechanisms are observed for the same laser settings and surrounding gas. At a laser fluence of 5 J/cm2, phase explosion appears to be the ablation mechanism in case of Zn, while for Ti normal vaporisation seems to be the dominant mechanism. The results show that pulsed digital holographic interferometry is a promising technique to give a physical picture and increase the understanding of the laser ablation process in a time resolved manner.
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| 9. |
- Amer, Eynas, et al.
(författare)
-
Shock wave generation in laser ablation studied using pulsed digital holographic interferometry
- 2008
-
Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 41:21
-
Tidskriftsartikel (refereegranskat)abstract
- Pulsed digital holographic interferometry has been used to study the shock wave induced by a Q-switched Nd-YAG laser (λ = 1064 nm and pulse duration 12 ns) on a polycrystalline boron nitride (PCBN) ceramic target under atmospheric air pressure. A special setup based on using two synchronized wavelengths from the same laser for processing and measurement simultaneously has been introduced. Collimated laser light (λ = 532 nm) passed through the volume along the target and digital holograms were recorded for different time delays after processing starts. Numerical data of the integrated refractive index field were calculated and presented as phase maps showing the propagation of the shock wave generated by the process. The location of the induced shock wave front was observed for different focusing and time delays. The amount of released energy, i.e. the part of the incident energy of the laser pulse that is eventually converted to a shock wave has been estimated using the point explosion model. The released energy is normalized by the incident laser pulse energy and the energy conversion efficiency between the laser pulse and PCBN target has been calculated at different power densities. The results show that the energy conversion efficiency seems to be constant around 80% at high power densities.
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| 10. |
- Amer, Eynas, et al.
(författare)
-
Single-shot polarization digital holography for recording stimulated Raman scattering signal for time-resolved measurement of gaseous species
- 2017
-
Ingår i: Applied Optics. - : Optical Society of America. - 1559-128X .- 2155-3165. ; 56:36, s. 10016-10023
-
Tidskriftsartikel (refereegranskat)abstract
- The stimulated Raman scattering (SRS) process is sensitive to the relation between the polarization direction of the two laser beams (the pump and the Stokes) that generate it. In this paper, we made use of the polarization sensitivity of the SRS process and used polarization-resolved pulsed digital holography to record the signal from one single-shot hologram. The pump beam polarization was kept vertical, while the Stokes beam polarization was 45 deg. The two polarization components of the Stokes beam were recorded in a single hologram by blending the Stokes beam with two reference beams with orthogonal polarization on the detector. The two components of the Stokes beam were separated in the Fourier domain, and the corresponding intensity maps were calculated. The vertically polarized component of the Stokes beam was amplified due to the SRS process, while the horizontal component experienced no gain. The difference between the vertically and horizontally polarized intensity maps, respectively, was calculated and Fourier transformed to separate the gain signal in the spatial frequency domain. The method was demonstrated on methane (CH4) gas at a pressure of 12 bars. Results show that SRS polarization holography is a promising technique for recording the SRS signal from one single-shot hologram for time-resolved monitoring of specific species.
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| 11. |
- Amer, Eynas, et al.
(författare)
-
Stimulated laser induced fluorescence holography for imaging fluorescent species
- 2013
-
Ingår i: Optics Communications. - : Elsevier BV. - 0030-4018 .- 1873-0310. ; 311, s. 124-128
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper pulsed digital holographic detection is coupled to the stimulated laser induced fluorescence (LIF) effect for imaging fluorescent species. A frequency tripled Q-switched Nd-YAG laser (wavelength 355 nm, pulse duration 12 ns) has been used to pump Coumarin 153 dye solved in ethanol. Simultaneously a frequency doubled pulse (532 nm) from the same laser is used to probe the solvent resulting in a gain through stimulated emission. The resulting gain of the probe beam is recorded using digital holography by blending it with a reference beam on the detector. Intensity maps were calculated from the recorded digital holograms and used to calculate the gain of the probe beam due to stimulated fluorescence emission which is coupled to the concentration of the dye. The results show that the amplification of the probe beam (532 nm) due to stimulated LIF emission is seen in the intensity maps. The gain is about 40% at a dye concentration of 0.32 g/L and decreases to be about 20% at a dye concentration of 0.04 g/L for a probe beam energy density of 0.1 mJ/cm2. Spectroscopic measurements have been carried out to confirm the holographic results. The results show that stimulated LIF holography is a promising technique for quantitative imaging of fluorescent species.
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| 12. |
- Amer, Eynas, et al.
(författare)
-
Stimulated LIF studied using pulsed digital holography and modelling
- 2013
-
Ingår i: Optical Measurement Systems for Industrial Inspection VIII. - : SPIE - International Society for Optical Engineering. - 9780819496041
-
Konferensbidrag (refereegranskat)abstract
- A frequency tripled Q-switched Nd-YAG laser (wavelength 355 nm, pulse duration 12 ns) has been used to pump Coumarin 153 dye solved in ethanol. The laser induced fluorescence (LIF) spectrum has been recorded using a spectrometer at different dye concentrations. The frequency doubled 532 nm beam from the same laser is used as a probe beam to pass through the excited volume of the dye. Because of stimulated emission an increase of the probe (532 nm) beam energy is recorded and a reduction of the spontaneous fluorescence spectrum intensity is observed. A model was developed that approaches the trend of the gain as a function of the probe beam energy at low dye concentrations (less than 0.08 g/L). The stimulated LIF is further recorded using digital holography. Digital holograms were recorded for different dye concentrations using collimated laser light (532 nm) passed through the dye volume. Two holograms without and with the UV laser beam were recorded. Intensity maps were calculated from the recorded digital holograms and are used to calculate the gain of the green laser beam due to the stimulated fluorescence emission which is coupled to the dye concentration. The gain of the coherent 532 nm beam is seen in the intensity maps and its value is about 40% for a dye concentration of 0.32 g/L and decreases with the decrease of the dye concentration. The results show that pulsed digital holography can be coupled to the stimulated LIF effect for imaging fluorescent species
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| 13. |
- Amer, Eynas, et al.
(författare)
-
Stimulated Raman scattering detection for chemically specific time-resolved imaging of gases
- 2016
-
Ingår i: Optics Express. - 1094-4087. ; 24:9, s. 9984-9993
-
Tidskriftsartikel (refereegranskat)abstract
- stimulated Raman scattering (SRS) imaging technique based on spatial modulation of the pump beam has been used to study gases. The SRS gain signal was separated from the Stokes beam background in the spatial frequency domain. The SRS signal shows linear behaviour with the gas pressure at a range from 1.0 to 8.0 bars. The signal is linearly proportional to the pump beam intensity while it is enhanced with increasing the Stokes beam intensity to a certain limit than it saturates. Further, the chemical specificity of the technique has been investigated. Two sharp peaks with line width at half maximum of about 0.30 nm have been obtained at Stokes beam wavelengths of 629.93 nm and 634.05 nm corresponding to the methane and ethylene gases, respectively. The results show that SRS imaging is a promising technique to provide chemical specificity as well as spatial and temporal information of gaseous species
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| 14. |
- Amer, Eynas, et al.
(författare)
-
Stimulated Raman scattering holography for time-resolved imaging of methane gas
- 2016
-
Ingår i: Applied Optics. - 1559-128X .- 2155-3165. ; 55:13, s. 3429-3434
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, pulsed digital holographic detection is coupled to the stimulated Raman scattering (SRS) process for imaging gases. A Q-switched Nd-YAG laser (532 nm) has been used to pump methane gas (CH4) at pressures up to 12 bars. The frequency-tripled (355 nm) beam from the same laser was used to pump an optical parametric oscillator (OPO). The Stokes beam (from the OPO) has been tuned to 629.93 nm so that the frequency difference between the pump (532 nm) and the Stokes beams fits a Raman active vibrational mode of the methane molecule (2922 cm(-1)). The pump beam has been spatially modulated with fringes produced in a Michelson interferometer. The pump and the Stokes beams were overlapped in time, space, and polarization on the gas molecules, resulting in a stimulated Raman gain of the Stokes beam and a corresponding loss of the pump beam through the SRS process. The resulting gain of the Stokes beam has been detected using pulsed digital holography by blending it with a reference beam on the detector. Two holograms of the Stokes beam, without and with the pump beam fringes present, were recorded. Intensity maps calculated from the recorded digital holograms showed amplification of the Stokes beam at the position of overlap with the pump beam fringes and the gas molecules. The gain of the Stokes beam has been separated from the background in the Fourier domain. A gain of about 4.5% at a pump beam average intensity of 4 MW/cm(2) and a Stokes beam intensity of 0.16 MW/cm(2) have been recorded at a gas pressure of 12 bars. The gain decreased linearly with decreasing gas pressure. The results show that SRS holography is a promising technique to pinpoint a specific species and record its spatial and temporal distribution
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| 15. |
- Amer, Eynas, et al.
(författare)
-
Stimulated Raman scattering imaging for studying specific species
- 2015
-
Ingår i: SPECKLE 2015. - Washington : SPIE - International Society for Optical Engineering. - 9781628418781
-
Konferensbidrag (refereegranskat)abstract
- The stimulated Raman scattering (SRS) signal in diffuse light has been recorded using an optical imaging technique based on spatial modulation. A frequency doubled Q-switched Nd-YAG laser (wavelength 532 nm) has been used to pump a polymethyl methacrylate (PMMA) cylinder. The frequency tripled (355 nm) beam from the same laser is used to pump an optical parametric oscillator (OPO). The Stokes beam (from the OPO) has been tuned to 631.27 nm so that the frequency difference between the pump and the Stokes beams fits a Raman active vibrational mode of the PMMA molecule (2956 cm-1). The two laser beams were overlapped in time and space on a PMMA cylinder resulting in a gain of the Stokes beam through the SRS process of about 4.0 %. For separating the SRS signal, the pump beam was spatially modulated with fringes produced in a Michelson interferometer. The gain of the Stokes beam due to SRS was separated from the Stokes beam background in the Fourier domain. The intensity image has been calculated from an inverse Fourier transform of the separated gain signal. The intensity image shows a gain of the Stokes beam at the area of overlap between the pump beam fringes and the Stokes beam compared to the undisturbed surrounding. The results show that spatial modulation of the pump beam is a promising method to separate the weak SRS signal from the Stokes beam background. This technique can be applied to pin-point specific species and record its spatial and temporal distribution
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| 16. |
- Amer, Eynas, et al.
(författare)
-
Stimulated Raman scattering signals recorded by the use of an optical imaging technique
- 2015
-
Ingår i: Applied Optics. - 1559-128X .- 2155-3165. ; 54:20, s. 6377-6385
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, stimulated Raman scattering (SRS) signals have been recorded by an optical imaging technique that is based on spatial modulation. A frequency doubled Q-switched Nd:YAG laser (532 nm) was used to pump a polymethyl methacrylate (PMMA) target. The frequency tripled (355 nm) beam from the same laser was used to pump an optical parametric oscillator (OPO). The Stokes beam (from the OPO) was tuned to 631.27 nm so that the frequency difference between the pump and the Stokes beams fit the Raman active vibrational mode of the PMMA molecule (2956 cm(-1)). The pump beam has been spatially modulated with fringes produced in a Michelson interferometer. The pump and the Stokes beams were overlapped on the target resulting in a gain of the Stokes beam of roughly 2.5% and a corresponding loss of the pump beam through the SRS process. To demodulate the SRS signal, two images of the Stokes beam without and with the pump beam fringes present were recorded. The difference between these two images was calculated and Fourier transformed. Then, the gain of the Stokes beam was separated from the background in the Fourier domain. The results show that spatial modulation of the pump beam is a promising method to separate the weak SRS signal from the background.
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| 17. |
- Amer, Eynas, et al.
(författare)
-
Towards traceable dynamic pressure calibration using a shock tube with an optical probe for accurate phase determination
- 2022
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Ingår i: Metrologia. - : IOP Publishing. - 0026-1394 .- 1681-7575. ; 59:3
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, we introduce a robust method for dynamic characterization of pressure measuring systems used in time-varying pressure applications. The dynamic response of the pressure measuring systems in terms of sensitivity and phase as a function of frequency at various amplitudes of the measurand can be provided. The shock tube which is the candidate primary standard for dynamic pressure calibration at the National Laboratory for pressure, Sweden, was used to realize the dynamic pressure. The shock tube setup used in this study can realize reference pressure with amplitudes up to 1.7 MPa in the frequency range from below a kilohertz up to a megahertz. The amplitude of the realized step pressure was calculated using the Rankine–Hugoniot step relations. In addition, the accurate time of arrival of the generated shock at the device under test (DUT) was measured using an optical probe based on shadowgraphy. The optical detector has a response time in nanosecond time scale which is several orders of magnitude faster than the response time of any pressure measuring system. Hereby, the latency between physical stimuli and response of the DUT can be measured. By the knowledge of the amplitude and the accurate time of arrival of the reference step pressure, the transfer function of the DUT can be calculated and presented in Bode diagrams of sensitivity and phase response versus frequency. The uncertainty in sensitivity and phase measurements was estimated. The information provided by this work is useful for developing reliable models of dynamic pressure measuring system and provide accurate information about their dynamic response. That in turn will contribute to establish a traceability chain for dynamic pressure calibration.
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| 18. |
- Amer, Eynas, et al.
(författare)
-
UV laser interaction with a fluorescent dye solution studied using pulsed digital holography
- 2013
-
Ingår i: Optics Express. - 1094-4087. ; 21:21, s. 25316-25323
-
Tidskriftsartikel (refereegranskat)abstract
- A frequency tripled Q-switched Nd-YAG laser (wavelength 355 nm, pulse duration 12 ns) has been used to pump Coumarin 153 dye solved in ethanol. Simultaneously, a frequency doubled pulse (532 nm) from the same laser is used to probe the solvent perpendicularly resulting in a gain through stimulated laser induced fluorescence (LIF) emission. The resulting gain of the probe beam is recorded using digital holography by blending it with a reference beam on the detector. Two digital holograms without and with the pump beam were recorded. Intensity maps were calculated from the recorded digital holograms and used to calculate the gain of the probe beam due to the stimulated LIF. In addition numerical data of the local temperature rise was calculated from the corresponding phase maps using Radon inversion. It was concluded that about 15% of the pump beam energy is transferred to the dye solution as heat while the rest is consumed in the radiative process. The results show that pulsed digital holography is a promising technique for quantitative study of fluorescent species
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| 19. |
- Field, J.E., et al.
(författare)
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High-speed photographic study of laser damage and ablation
- 2015
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Ingår i: Imaging Science Journal. - 1368-2199 .- 1743-131X. ; 63:3, s. 119-136
-
Tidskriftsartikel (refereegranskat)abstract
- This paper reviews earlier work and describes a photographic investigation of damage produced in glasses, polymers and crystals by Q-switched and non-Q-switched laser pulses. The cameras used in the study include a Wollensak Fastax WF3 camera, a Beckman & Whitley (model 189) rotating mirror camera, and a Beckman & Whitley (model 501) image converter camera. The formation of internal disc-type cracks with the non-Q-switched pulse was studied in detail. The use of these cracks for fracture energy studies is demonstrated. Photographic sequences show the production of micro-plasmas associated with damage, and stress waves formed during irradiation in both solids and liquids. A recent development is that of digital holography which adds phase and intensity information to the more conventional photographic techniques. This technique is used here to study laser ablation and wave propagation in water. The photographic data shows the processes taking place in the laser interaction with a wide range of materials and should be of interest to modellers.
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| 20. |
- Forssén, Clayton, et al.
(författare)
-
Demonstration of a transportable Fabry–Pérot refractometer by a ring-type comparison of dead-weight pressure balances at four European national metrology institutes
- 2024
-
Ingår i: Sensors. - : MDPI. - 1424-8220. ; 24:1
-
Tidskriftsartikel (refereegranskat)abstract
- Fabry–Pérot-based refractometry has demonstrated the ability to assess gas pressure with high accuracy and has been prophesized to be able to realize the SI unit for pressure, the pascal, based on quantum calculations of the molar polarizabilities of gases. So far, the technology has mostly been limited to well-controlled laboratories. However, recently, an easy-to-use transportable refractometer has been constructed. Although its performance has previously been assessed under well-controlled laboratory conditions, to assess its ability to serve as an actually transportable system, a ring-type comparison addressing various well-characterized pressure balances in the 10–90 kPa range at several European national metrology institutes is presented in this work. It was found that the transportable refractometer is capable of being transported and swiftly set up to be operational with retained performance in a variety of environments. The system could also verify that the pressure balances used within the ring-type comparison agree with each other. These results constitute an important step toward broadening the application areas of FP-based refractometry technology and bringing it within reach of various types of stakeholders, not least within industry.
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| 21. |
- Khodadad, Davood, et al.
(författare)
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Single-shot dual-polarization holography : measurement of the polarization state of a magnetic sample
- 2015
-
Ingår i: SPECKLE 2015. - : SPIE - International Society for Optical Engineering. - 9781628418781
-
Konferensbidrag (refereegranskat)abstract
- In this paper a single-shot digital holographic set-up with two orthogonally polarized reference beams is proposed to achieve rapid acquisition of Magneto-Optical Kerr Effect images. Principles of the method and the background theory for dynamic state of polarization measurement by use of digital holography are presented. This system has no mechanically moving elements or active elements for polarization control and modulation. An object beam is combined with two reference beams at different off-axis angles and is guided to a detector. Then two complex fields (interference terms) representing two orthogonal polarizations are recorded in a single frame simultaneously. Thereafter the complex fields are numerically reconstructed and carrier frequency calibration is done to remove aberrations introduced in multiplexed digital holographic recordings. From the numerical values of amplitude and phase, a real time quantitative analysis of the polarization state is possible by use of Jones vectors. The technique is demonstrated on a magnetic sample that is a lithographically patterned magnetic microstructure consisting of thin permalloy parallel stripes.
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| 22. |
- Sjödahl, Mikael, et al.
(författare)
-
Depth resolution of phase gradients using pulsed digital holography
- 2010
-
Ingår i: Biomedical optics (BIOMED). - Washington, DC : Optical Society of America. - 9781557528872
-
Konferensbidrag (refereegranskat)abstract
- technique to gain depth information from a single pair image-plane Digital Holographic recording of a transient phase object positioned between a diffuser and an imaging system has been demonstrated
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| 23. |
- Sjödahl, Mikael, et al.
(författare)
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Depth-resolved measurement of phase gradients in a transient phase object field using pulsed digital holography
- 2009
-
Ingår i: Applied Optics. - 1559-128X .- 2155-3165. ; 48:34, s. H31-H39
-
Tidskriftsartikel (refereegranskat)abstract
- A technique to gain depth information from an image-plane digital holographic recording of a transient phase object positioned between a diffuser and an imaging system is demonstrated. The technique produces telecentric reconstructions of the complex amplitude throughout the phase volume using numerical lenses and the complex spectrum formulation of the diffraction integral. The in-plane speckle movements as well as the phase difference between the disturbed field and a reference field are calculated in a finite number of planes using a cross-correlation formulation. It is shown that depth information about in-plane phase gradients can be determined in two planes using reconstructed speckle fields from four different depths. In addition, the plane of optimum reconstruction for calculating the phase difference with maximum contrast is detected from the technique. The method is demonstrated on a measurement of a laser ablation process.
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| 24. |
- Sjödahl, Mikael, 1965-, et al.
(författare)
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Quantitative measurement of thin phase objects : comparison of speckle deflectometry and defocus-variant lateral shear interferometry
- 2018
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Ingår i: Applied Optics. - : Optical Society of America. - 1559-128X .- 2155-3165. ; 57:14, s. 3645-3652
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Tidskriftsartikel (refereegranskat)abstract
- The two techniques of lateral shear interferometry and speckle deflectometry are analyzed in a common optical system for their ability to measure phase gradient fields of a thin phase object. The optical system is designed to introduce a shear in the frequency domain of a telecentric imaging system that gives a sensitivity of both techniques in proportion to the defocus introduced. In this implementation, both techniques successfully measure the horizontal component of the phase gradient field. The response of both techniques scales linearly with the defocus distance, and the precision is comparative, with a random error in the order of a few rad/mm. It is further concluded that the precision of the two techniques relates to the transverse speckle size in opposite ways. While a large spatial coherence width, and correspondingly a large lateral speckle size, makes lateral shear interferometry less susceptible to defocus, a large lateral speckle size is detrimental for speckle correlation. The susceptibility for the magnitude of the defocus is larger for the lateral shear interferometry technique as compared to the speckle deflectometry technique. The two techniques provide the same type of information; however, there are a few fundamental differences. Lateral shear interferometry relies on a special hardware configuration in which the shear angle is intrinsically integrated into the system. The design of a system sensitive to both in-plane phase gradient components requires a more complex configuration and is not considered in this paper. Speckle deflectometry, on the other hand, requires no special hardware, and both components of the phase gradient field are given directly from the measured speckle deformation field.
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| 25. |
- Svete, A., et al.
(författare)
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A method for correcting the high-frequency mechanical vibration effects in the dynamic calibration of pressure measurement systems using a shock tube
- 2023
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Ingår i: Mechanical systems and signal processing. - : Elsevier BV. - 0888-3270 .- 1096-1216. ; 193
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Tidskriftsartikel (refereegranskat)abstract
- The extremely rapid reflection of a shock wave from the end wall generated in the shock tube, in addition to the high-frequency content of pressure, inevitably also excites mechanical vibrations. These can potentially produce acceleration-induced spurious signals as part of the dynamic output of the pressure measurement system being calibrated. This paper proposes and evaluates a method for correcting the frequency response of a pressure measurement system obtained with a calibration using a shock tube for the acceleration-induced errors due to vibrations. The proposed method is based on the predetermined frequency response of the pressure measurement system to the accelerations and simultaneous measurements of the vibration accelerations of the pressure sensor during its calibration in the shock tube. The acceleration-induced errors were corrected for a piezoelectric pressure measurement system calibrated in a diaphragmless shock tube developed at the National laboratory for pressure and vacuum at RISE Research Institutes of Sweden, where different vibrational conditions were induced by changing the initial driver pressure, while keeping the initial driven pressure constant. The uncertainty of the correction of the frequency response of the piezoelectric pressure measurement system being calibrated was determined by considering the uncertainty contributions of the measured acceleration frequency response of the pressure measurement system, the measured acceleration of the pressure sensor during its calibration in the shock tube, the generated reference end-wall step pressure and the repeatability of the correction. The results show that the proposed method effectively eliminates acceleration-induced errors in the sensitivity and phase frequency responses of an acceleration-sensitive piezoelectric pressure measurement system being calibrated with a shock tube.
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