| 1. |
- Abramson, Nils H.
(författare)
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Elliptic visualizing optical resolution and kinetic energy
- 2017
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Ingår i: Applied Optics. - : Optical Society of America. - 1559-128X .- 2155-3165. ; 56:5, s. 1413-1416
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Tidskriftsartikel (refereegranskat)abstract
- Diffraction limited resolution as introduced by Abbe is well established, but interference limited resolution was not well known until holographic interferometry was introduced. The holodiagram is used to simplify holography and in a new way visualize the distribution, ratio, and relation among resolutions of different optical techniques, including relativistic phenomena. Resolution, when measured by optical methods based on the number of wavelengths of light, is defined in the following as the minimum distance between resolvable points, or the largest object needed to be resolved. Everywhere in the diagram this resolution is represented by two orthogonal diagonals of rhombs.
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| 2. |
- Amer, Eynas, et al.
(författare)
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Single-shot polarization digital holography for recording stimulated Raman scattering signal for time-resolved measurement of gaseous species
- 2017
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Ingår i: Applied Optics. - : Optical Society of America. - 1559-128X .- 2155-3165. ; 56:36, s. 10016-10023
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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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| 3. |
- Amer, Eynas, et al.
(författare)
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Stimulated Raman scattering holography for time-resolved imaging of methane gas
- 2016
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Ingår i: Applied Optics. - 1559-128X .- 2155-3165. ; 55:13, s. 3429-3434
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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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| 4. |
- Amer, Eynas, et al.
(författare)
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Stimulated Raman scattering signals recorded by the use of an optical imaging technique
- 2015
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Ingår i: Applied Optics. - 1559-128X .- 2155-3165. ; 54:20, s. 6377-6385
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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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| 5. |
- Barrios, David, et al.
(författare)
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Inversion of two-flux and four-flux radiative transfer models for determining scattering and absorption coefficients for a suspended particle device
- 2019
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Ingår i: Applied Optics. - : OPTICAL SOC AMER. - 1559-128X .- 2155-3165. ; 58:32, s. 8871-8881
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Tidskriftsartikel (refereegranskat)abstract
- Intrinsic and extrinsic scattering and absorption coefficients of a suspended particle device (SPD) smart window sample at dark and dear appearance states-without and with applied electrical voltage, respectively-were determined by means of the Maheu, Letoulouzan, and Gouesbet four-flux (intrinsic) and Kubelka-Munk two-flux ( extrinsic) radiative transfer models, respectively. Extrinsic values were obtained from fitting to the two-flux model taking into account the predominantly forward scattering of the SPD. As an approximation, the Fresnel reflection coefficients were integrated out to the critical angle of total internal reflection in order to compute diffuse interface reflectances. Intrinsic coefficients were retrieved by adding a new proposed approximation for the average crossing parameter based on the collimated and diffuse light intensities at each interface. This approximation, although an improvement of previous approaches, is not entirely consistent with the two-flux model results. However, it paves the way for further development of methods to solve the inverse problem of the four-flux model.
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| 6. |
- Boyko, Andrey A., et al.
(författare)
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Intracavity difference-frequency mixing of optical parametric oscillator signal and idler pulses in BaGa4Se7
- 2017
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Ingår i: Applied Optics. - : OPTICAL SOC AMER. - 1559-128X .- 2155-3165. ; 56:10, s. 2783-2786
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Tidskriftsartikel (refereegranskat)abstract
- An overall quantum conversion efficiency of 7.8% is achieved by intracavity mixing the signal and idler of a 1.064 mu m pumped Rb: PPKTP optical parametric oscillator in BaGa4Se7. In this way, a pulse energy of similar to 0.71 mJ is generated at similar to 7 mu m for a repetition rate of 100 Hz. Tuning of the mid-IR radiation is demonstrated by heating of the Rb: PPKTP crystal.
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| 7. |
- Chang, Jin, et al.
(författare)
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Multimode-fiber-coupled superconducting nanowire single-photon detectors with high detection efficiency and time resolution
- 2019
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Ingår i: Applied Optics. - : Optical Society of America. - 1559-128X .- 2155-3165. ; 58:36, s. 9803-9807
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Tidskriftsartikel (refereegranskat)abstract
- In the past decade, superconducting nanowire single-photon detectors (SNSPDs) have gradually become an indispensable part of any demanding quantum optics experiment. Until now, most SNSPDs have been coupled to single-mode fibers. SNSPDs coupled to multimode fibers have shown promising efficiencies but have yet to achieve high time resolution. For a number of applications ranging from quantum nano-photonics to bio-optics, high efficiency and high time resolution are desired at the same time. In this paper, we demonstrate the role of polarization on the efficiency of multimode-fiber-coupled detectors and fabricated high-performance 20 mu m, 25 mu m, and 50 mu m diameter detectors targeted for visible, near-infrared, and telecom wavelengths. A custom-built setup was used to simulate realistic experiments with randomized modes in the fiber. We achieved over 80% system efficiency and <20 ps timing jitter for 20 mu m SNSPDs. Also, we realized 70% system efficiency and <20 ps timing jitter for 50 mu m SNSPDs. The high-efficiency multimode-fiber-coupled SNSPDs with unparalleled time resolution will benefit various quantum optics experiments and applications in the future.
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| 8. |
- Chen, Hongzhi, et al.
(författare)
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Terahertz polarization splitter based on a dual-elliptical-core polymer fiber
- 2016
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Ingår i: Applied Optics. - : OPTICAL SOC AMER. - 1559-128X .- 2155-3165. ; 55:23, s. 6236-6242
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Tidskriftsartikel (refereegranskat)abstract
- A terahertz polarization splitter based on a dual-elliptical-core polymer fiber is proposed and theoretically optimized. Dual-elliptical cores with subwavelength-scale diameters are independently suspended within a fiber, which not only support two orthogonal polarization modes, being single-mode guided with low absorption losses, but also allow them to switch from one core to the other, with different coupling lengths. As a consequence, the two polarizations can be easily separated by choosing a suitable transmission length at a desired operation frequency. The transmission modes, coupling lengths for x- and y-polarizations, as well as the performance of the proposed polarization splitter at a center-frequency of 0.6 THz are investigated and numerically analyzed. A 1.43 cm long splitter with an ultralow loss of 0.4 dB, a high extinction ratio better than -10 dB and a bandwidth of 0.02 THz is achieved.
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| 9. |
- Daemi, Bita, et al.
(författare)
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Advanced image analysis verifies geometry performance of micro-milling systems
- 2017
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Ingår i: Applied Optics. - : OPTICAL SOC AMER. - 1559-128X .- 2155-3165. ; 56:10, s. 2912-2921
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Tidskriftsartikel (refereegranskat)abstract
- Accurate dimensional measurement of micro-milled items is a challenge and machine specifications do not include operational parameters in the workshop. Therefore, a verification test that shows the machine's overall geometrical performance over its working area would help machine users in the assessment and adjustment of their equipment. In this study, we present an optical technique capable of finding micro-milled features at submicron uncertainty over working areas > 10 cm(2). The technique relies on an ultra-precision measurement microscope combined with advanced image analysis to get the center of gravity of milled cross-shaped features at subpixel levels. Special algorithms had to be developed to handle the disturbing influence of burr and milling marks. The results show repeatability, reproducibility, and axis straightness for three micro-milling facilities and also discovered an unknown 2 mu m amplitude undulation in one of them.
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| 10. |
- Goenka, Chhavi, et al.
(författare)
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Multichannel tunable imager architecture for hyperspectral imaging in relevant spectral domains
- 2016
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Ingår i: Applied Optics. - : Optical Society of America. - 1559-128X .- 2155-3165. ; 55:12, s. 3149-3157
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we present a technique for dimensionality reduction in hyperspectral imaging during the data collection process. A four-channel hyperspectral imager using liquid crystal Fabry-Perot etalons has been built and used to verify this method for four applications: auroral imaging, plant study, landscape classification, and anomaly detection. This imager is capable of making measurements simultaneously in four wavelength ranges while being tunable within those ranges, and thus can be used to measure narrow contiguous bands in four spectral domains. In this paper, we describe the design, concept of operation, and deployment of this instrument. The results from preliminary testing of this instrument are discussed and are promising and demonstrate this instrument as a good candidate for hyperspectral imaging.
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