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Blue Laser Source for Laser-Induced Fluorescence

Holm, Jesper LU (2008) In Lund Reports in Atomic Physics LRAP-396.
Abstract
Laser-induced fluorescence is a clinical diagnostic tool, used for tumor demarcation and detection. The technique relies on the injection or topical application of a light sensitive drug called a photosensitizer. This substance has the ability to be accumulated to higher concentrations in cancer cells than in normal cells. This accumulation procedure takes from a few hours to several days, depending on the photosensitizer used. When the photosensitizer is illuminated with 405 nm light it will fluoresce in the red spectral region. The difference in photosensitizer concentration from cancer cells to noncancer cells can therefore be detected as a change

in the fluorescence level. Two photosensitizers were used in this work: ALA-induced... (More)
Laser-induced fluorescence is a clinical diagnostic tool, used for tumor demarcation and detection. The technique relies on the injection or topical application of a light sensitive drug called a photosensitizer. This substance has the ability to be accumulated to higher concentrations in cancer cells than in normal cells. This accumulation procedure takes from a few hours to several days, depending on the photosensitizer used. When the photosensitizer is illuminated with 405 nm light it will fluoresce in the red spectral region. The difference in photosensitizer concentration from cancer cells to noncancer cells can therefore be detected as a change

in the fluorescence level. Two photosensitizers were used in this work: ALA-induced PpIX and mTHPC. A high power laser system is needed in order for the fluorescence detection to work when imaging large areas in real time. The suppression of the ambient lighting can be overcome using a pulsed laser system combined with a time gated camera.

In this thesis such a laser system has been developed. Several factors were constraining the system, as it needed to be mobile, clinical certifiable, inexpensive and ompact, all in order for easy operation in a clinical setting. The target wavelength of the system was 405 nm, and this was realized by doubling the output of an 810 nm diode laser. In order to generate sufficient power at 810 nm, an external cavity tapered laser amplifier system was constructed. It consists of a tapered diode, that were anti-reflection coated on both the front and back facets. On the back facet, a collimating lens is directing the output beam towards a diffraction grating, used in the Littrow configuration, that spectrally stabilizes the laser system and determines the operating wavelength. The 1st order diffracted beam from the grating was coupled directly back

into the amplifier, resulting in an output beam from the laser diode with 1.9 W of output power at 810 nm. The tuning range of this system was 30 nm and could be achieved be a simple rotation of the diffraction grating.

In order to effectively frequency double the 810 nm laser beam, an external resonator containing a periodically poled KTP crystal was constructed. Periodically poled KTP was found to be susceptible to a photochromic damage called grey-tracking, at the power levels needed for generation of the 405 nm output beam. A

very compact resonator design was used, as it allowed for a large acceptance bandwidth from the pump laser.

For stable continuous wave operation the external resonator needed to be phase locked, using a polarization sensitive electronic circuitry. An output power of 300 mW at the target wavelength of 405 nm was obtained from this external resonator system. Thermal issues in the crystal was severely limiting the output power of the system, necessitating the use of a very long nonlinear crystal of 30 mm in length. The pulsed laser source was realized by scanning the external resonator on and off resonance and more than 700 mW of output power was obtained. Both the continuous wave and pulsed laser systems were clinically used on patients diagnosed with skin cancer and underwent photodynamic therapy. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Prof. Dr Loosen, Peter, Fraunhofer-Institut für Lasertechnik ILT, Aachen, Tyskland
publishing date
type
Thesis
publication status
published
subject
keywords
Second Harmonic Generation, Lasers, PPKTP, ALA, Tapered laser diodes, External cavity lasers, Laser-induced fluorescence, photodynamic therapy, mTHPC
in
Lund Reports in Atomic Physics
volume
LRAP-396
pages
113 pages
publisher
Atomic Physics, Department of Physics, Lund University
defense location
Room B, Department of Physics, Professorsgatan 1, Lund University, Faculty of Engineering
defense date
2008-09-05 10:15
ISBN
978-91-628-7570-1
language
English
LU publication?
no
id
4d4010f7-a808-4476-835d-048b8bf1a4bc (old id 1213037)
date added to LUP
2008-08-13 11:26:43
date last changed
2016-09-19 08:45:13
@phdthesis{4d4010f7-a808-4476-835d-048b8bf1a4bc,
  abstract     = {Laser-induced fluorescence is a clinical diagnostic tool, used for tumor demarcation and detection. The technique relies on the injection or topical application of a light sensitive drug called a photosensitizer. This substance has the ability to be accumulated to higher concentrations in cancer cells than in normal cells. This accumulation procedure takes from a few hours to several days, depending on the photosensitizer used. When the photosensitizer is illuminated with 405 nm light it will fluoresce in the red spectral region. The difference in photosensitizer concentration from cancer cells to noncancer cells can therefore be detected as a change<br/><br>
in the fluorescence level. Two photosensitizers were used in this work: ALA-induced PpIX and mTHPC. A high power laser system is needed in order for the fluorescence detection to work when imaging large areas in real time. The suppression of the ambient lighting can be overcome using a pulsed laser system combined with a time gated camera.<br/><br>
 In this thesis such a laser system has been developed. Several factors were constraining the system, as it needed to be mobile, clinical certifiable, inexpensive and ompact, all in order for easy operation in a clinical setting. The target wavelength of the system was 405 nm, and this was realized by doubling the output of an 810 nm diode laser. In order to generate sufficient power at 810 nm, an external cavity tapered laser amplifier system was constructed. It consists of a tapered diode, that were anti-reflection coated on both the front and back facets. On the back facet, a collimating lens is directing the output beam towards a diffraction grating, used in the Littrow configuration, that spectrally stabilizes the laser system and determines the operating wavelength. The 1st order diffracted beam from the grating was coupled directly back<br/><br>
into the amplifier, resulting in an output beam from the laser diode with 1.9 W of output power at 810 nm. The tuning range of this system was 30 nm and could be achieved be a simple rotation of the diffraction grating.<br/><br>
 In order to effectively frequency double the 810 nm laser beam, an external resonator containing a periodically poled KTP crystal was constructed. Periodically poled KTP was found to be susceptible to a photochromic damage called grey-tracking, at the power levels needed for generation of the 405 nm output beam. A<br/><br>
very compact resonator design was used, as it allowed for a large acceptance bandwidth from the pump laser.<br/><br>
 For stable continuous wave operation the external resonator needed to be phase locked, using a polarization sensitive electronic circuitry. An output power of 300 mW at the target wavelength of 405 nm was obtained from this external resonator system. Thermal issues in the crystal was severely limiting the output power of the system, necessitating the use of a very long nonlinear crystal of 30 mm in length. The pulsed laser source was realized by scanning the external resonator on and off resonance and more than 700 mW of output power was obtained. Both the continuous wave and pulsed laser systems were clinically used on patients diagnosed with skin cancer and underwent photodynamic therapy.},
  author       = {Holm, Jesper},
  isbn         = {978-91-628-7570-1},
  keyword      = {Second Harmonic Generation,Lasers,PPKTP,ALA,Tapered laser diodes,External cavity lasers,Laser-induced fluorescence,photodynamic therapy,mTHPC},
  language     = {eng},
  pages        = {113},
  publisher    = {Atomic Physics, Department of Physics, Lund University},
  series       = {Lund Reports in Atomic Physics},
  title        = {Blue Laser Source for Laser-Induced Fluorescence},
  volume       = {LRAP-396},
  year         = {2008},
}