| 1. |
- Cheng, Haynes P. H., et al.
(författare)
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Autofluorescence of pigmented skin lesions using a pulsed UV laser
- 2010
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Ingår i: Proceedings of SPIE. - : SPIE. ; 7715, s. 1-77151
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Konferensbidrag (refereegranskat)abstract
- We report preliminary clinical results of autofluorescence imaging of malignant and benign skin lesions, using pulsed 355 nm laser excitation with synchronized detection. The novel synchronized detection system allows high signal-tonoise ratio to be achieved in the resulting autofluorescence signal, which may in turn produce high contrast images that improve diagnosis, even in the presence of ambient room light. The synchronized set-up utilizes a compact, diode pumped, pulsed UV laser at 355 nm which is coupled to a CCD camera and a liquid crystal tunable filter. The excitation and image capture is sampled at 5 kHz and the resulting autofluorescence is captured with the liquid crystal filter cycling through seven wavelengths between 420 nm and 580 nm. The clinical study targets pigmented skin lesions and evaluates the prospects of using autofluorescence as a possible means in differentiating malignant and benign skin tumors. Up to now, sixteen patients have participated in the clinical study. The autofluorescence images, averaged over the exposure time of one second, will be presented along with histopathological results. Initial survey of the images show good contrast and diagnostic results show promising agreement based on the histopathological results.
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| 2. |
- Hogstedt, Lasse, et al.
(författare)
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Low-noise mid-IR upconversion detector for improved IR-degenerate four-wave mixing gas sensing
- 2014
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Ingår i: Optics Letters. - 0146-9592. ; 39:18, s. 5321-5324
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Tidskriftsartikel (refereegranskat)abstract
- We compare a nonlinear upconversion detector with a conventional cryogenic InSb detector for the detection of coherent infrared light showing near-shot-noise-limited performance in the upconversion system. The InSb detector is limited by dark noise, which results in a 500 times lower signal-to-noise ratio. The two detectors are compared for the detection of a coherent degenerate four-wave mixing (DFWM) signal in the mid-infrared, and applied to measure trace-level acetylene in a gas flow at atmospheric pressure, probing its fundamental rovibrational transitions. In addition to lower noise, the upconversion system provides image information of the signal, thus adding new functionality compared to standard point detection methods. We further show that the upconversion detector system can be implemented as a simple replacement of the cryogenic detector. (C) 2014 Optical Society of America
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| 3. |
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| 4. |
- Pedersen, Rasmus Lyngbye, et al.
(författare)
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Characterization of the NEP of mid-infrared upconversion detectors
- 2019
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Ingår i: IEEE Photonics Technology Letters. - 1041-1135. ; 31:9, s. 681-684
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Tidskriftsartikel (refereegranskat)abstract
- We present a scheme to estimate the noise equivalent power (NEP) of the frequency upconversion detectors (UCDs), detecting mid-infrared (MIR) light. The NEP of the UCD is a combined contribution of NEPs from the upconversion process and from the photodetector, used for detecting the upconverted signal. The 2-5- μm MIR range is particularly investigated in this letter using a bulk periodically poled lithium niobate-based CW-intracavity UCD. We measured the NEP of UCD as 20 fW Hz at the MIR wavelength of 3.39μm. Here, we showed that the limiting factor is not the noise from the upconversion process (estimated NEP is 2.3 fW Hz at 3.39 μm) but from the electrical noise in the photodetector itself. We also compared the performance of our UCD with the previously published results and with market available direct MIR detectors. In addition, we measured the optical noise of the UCD over its working spectral range (2.9- 3.6 μm) and compared with the numerical simulation.
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| 5. |
- Sahlberg, Anna-Lena, et al.
(författare)
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Upconversion imager improves IR gas sensing
- 2014
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Ingår i: Laser Focus World. - 1043-8092. ; 50:11, s. 51-53
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- A nonlinear upconversion detector shows near-shot-noise-limited performance and compares favorably-while adding additional imaging information-to conventional cryogenic detectors in the measurement of tracelevel gases at atmospheric pressure.
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| 6. |
- Tidemand-Lichtenberg, Peter, et al.
(författare)
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Nonlinear cavity dumping of a high finesse frequency mixing module
- 2007
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Ingår i: Optics Express. - 1094-4087. ; 15:15, s. 9799-9803
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Tidskriftsartikel (refereegranskat)abstract
- We present a novel generic approach for pulsed light generation in the visible spectrum. We demonstrate how the circulating field of a high finesse laser can be efficiently cavity dumped through sum- frequency mixing with externally injected high peak power single pass pulses. Periodically poled KTP is used as the nonlinear medium to minimize the peak power requirement of the injected beam. The experimental setup consists of a high finesse 1342 nm Nd:YVO4 laser cavity and a passively Q-switched Nd:YAG laser. Yellow pulses at 593 nm are generated.
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| 7. |
- Widarsson, Max, 1994-
(författare)
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Pulse Generation and Detection through Intra-Cavity Up-Conversion
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The work presented in this thesis concerns two main categories: pulse detection and pulse generation, however both utilise intra-cavity up-conversion. The work regarding pulse detection deals with up-conversion LIDAR and was split into two smaller projects, the first one focused on the resolution in measurements along one line with multiple reflections, and the second focused on measurements further into the MIR, as well as performing 3D imaging. The work on pulse generation was also split into two projects. In the first a solid-state laser was demonstrated that generated dark pulses, while the second project resulted in new way to achieve mode-locking and synchronously produced bright and dark pulses at two different wavelengths.The first LIDAR project utilised up-conversion detection 2.4 μm. The system had a temporal response of 42 ps (FWHM) and was able to detect two microscope slides separated by a few millimetres. In the second LIDAR project we pushed the LIDAR wavelength to slightly above 3 μm, and it was the longest wavelength that photon counting LIDAR had been performed at. The system could clearly resolve 1 mm deep features on a target and produce 3D images. Both the LIDAR systems used intra-cavity up-conversion with periodically poled rubidium doped KTiOPO4 (PPRKTP) in Nd:YVO4 lasers operating at 1064 nm.The dark pulse laser was based on sum-frequency generation (SFG) between a 1064 nm Nd:YVO4 laser and a mode-locked Yb-laser operating at 1040 nm. The mode-locked laser was focused into a PPRKTP placed inside the 1064 nm laser. By matching the cavity round-trip time of the 1064 nm laser to the repetition rate of the 1040 nm laser, the intensity dip produced by the SFG was enhanced for each round trip. The system could thereby produce dark pulses with a modulation depth of 90 % and a pulse width of 10 ps.In the last project bright pulses were produced by matching the cavity length of a 1064 nm Nd:YVO4 laser with that of a 1342 nm Nd:YVO4 laser. The two lasers formed a y-cavity, with a shared leg where a PPRKTP crystal was placed for phase-matched SFG between the two lasers. When the cavity lengths were matched, one laser produced bright mode-locked pulses and the other one dark pulses, synchronously. When the lasers enter this regime the SFG induced loss is significantly reduced due to the temporal overlap between the bright and dark pulse. The mode-locked pulses had a pulse width of 240 ps.
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