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Spectral Management in Quasi-Phase-Matched Parametric Devices
KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Nonlinear optical interaction in quasi-phase-matched structures opens up unique possibilities to build compact and efficient parametric devices such as optical parametric oscillators, generators, and amplifiers with tailored spectral properties. The focus of this thesis is on novel parametric interactions with periodically-poled KTiOPO4 (PPKTP) as the parametric gain medium.

Optical parametric oscillators (OPOs) are attractive light sources for many applications, particularly in spectroscopy, and plays a central role in this thesis. Special attention is put on simple, yet powerful, spectral-manipulation and bandwidth-narrowing techniques for OPOs. The overall knowledge gained from these studies has been used for device construction of several tunable ultraviolet sources for biological sensing.

In the case of bandwidth narrowing, the observation of decreasing spectral bandwidth in a noncollinear, idler-resonant OPO, as compared with a signal-resonant one, has been found to be due to the interplay between the material properties and the angular dispersion of PPKTP. To further reduce the bandwidth, we have shown that it is very beneficial to replace the output mirror in an OPO with a bulk Bragg grating. In fact, even close to degeneracy, where the bandwidth is typically wide, this approach is able to decrease the bandwidth drastically.

Moreover, different OPO cavity designs have been examined in order to spectrally manipulate the resonant waves. By deploying a grating in a ring OPO cavity, it becomes possible to access the resonant wave and spectrally manipulated it in a zero-dispersion arrangement; the filtered wave is subsequently sent back into its own cavity as a seed signal, in a self-seeding arrangement. This particular cavity design decreases the bandwidth close to ~ 1000 times as compare to the free-running mode. An interesting phenomenon arises when two mutually coherent laser beams are used to pump a linear OPO cavity. When the pump beams intersect within the PPKTP crystal, an interference grating is formed and acts as a catalyst for the generation of new spectral sidebands through multiple cascaded four-wave mixing, in the pump, the idler and the signal directions. The spacing of these sidebands is determined geometrically by the incident pump angle, while the signals are continuously tunable over the c-band telecom window (λ ~ 1.5 μm) by rotating the cavity.

Ultrabroad bandwidths have been generated in an optical parametric generator (OPG) pumped by an amplified picosecond Ti:sapphire laser. In the collinear direction the output spectrum extends over three octaves in the mid-infrared region. This enormously broad spectrum is also Fourier-filtered and subsequently used for narrowband seeding of an optical parametric amplifier (OPA).

Finally, the spectral range between 285 nm and 340 nm is of importance for detection of biological substances through fluorescence spectroscopy. With this spectral region in mind a practical way to generate a tunable parametric device in the ultraviolet region is presented in the thesis. The developed ultraviolet laser is used for studies of the characteristics of biological particles. The ultraviolet source and the results from these studies, will be utilized in an integrated detection system, a so called early-warning system.

Place, publisher, year, edition, pages
Stockholm: KTH , 2006. , 69 p.
Series
Trita-FYK, 2006:37
Keyword [en]
optical parametric devices, nonlinear optics, ultraviolet generation, mid-infrared generation, optical parametric oscillator, optical parametric generator, optical parametric amplifier
National Category
Atom and Molecular Physics and Optics
Identifiers
URN: urn:nbn:se:kth:diva-4021ISBN: 91-7178-379-2 (print)OAI: oai:DiVA.org:kth-4021DiVA: diva2:10434
Public defence
2006-06-13, Sal FD5, AlvaNova univ centrum, Roslagstullsbacken 21, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100923Available from: 2006-06-01 Created: 2006-06-01 Last updated: 2015-03-30Bibliographically approved
List of papers
1. Spectral and spatial limiting in an idler-resonant PPKTP optical parametric oscillator
Open this publication in new window or tab >>Spectral and spatial limiting in an idler-resonant PPKTP optical parametric oscillator
2005 (English)In: Optics Communications, ISSN 0030-4018, E-ISSN 1873-0310, Vol. 250, no 1-3, 207-211 p.Article in journal (Refereed) Published
Abstract [en]

The spectral and spatial properties of a non-collinear signal- and idler-resonant periodically poled KTiOPO4 optical parametric oscillator (OPO) have been investigated. The lower angular dispersion of the idler-resonant OPO allows for generation of up to two-times smaller spectral bandwidths at large non-collinear angles, and at the same time the beam quality improves considerably compared with the signal-resonant case. The overall efficiency reached 67% in both cases.

Keyword
non-linear effect, non-collinear optical parametric oscillator, idler-resonant
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-5897 (URN)10.1016/j.optcom.2005.02.020 (DOI)000229527900027 ()2-s2.0-18444387695 (Scopus ID)
Note
QC 20100923Available from: 2006-06-01 Created: 2006-06-01 Last updated: 2015-03-30Bibliographically approved
2. Narrowband bulk Bragg grating optical parametric oscillator
Open this publication in new window or tab >>Narrowband bulk Bragg grating optical parametric oscillator
2005 (English)In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 30, no 17, 2281-2283 p.Article in journal (Refereed) Published
Abstract [en]

A narrowband, pulsed optical parametric oscillator (OPO) whose output coupler is a bulk glass Bragg grating is demonstrated. The OPO is based on periodically poled KTiOPO4 and is pumped by a pulsed, frequency-doubled Nd:YAG laser at 532 nm, generating a signal at 975 nm with a total efficiency of 35%. This novel and compact device shows a spectral bandwidth of 0.16 nm (50 GHz), a decrease by a factor of 20 compared with that when a conventional mirror is used. By using a folded cavity, we demonstrate tunable radiation with a tuning range of 60 nm and maintained spectral bandwidth.

Keyword
Bandwidth; Mirrors; Radiation; Spectrum analysis; Bragg grating; Optical parametric oscillators (OPO); Spectral bandwidth; Tuning range
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-8206 (URN)10.1364/OL.30.002281 (DOI)000231436900031 ()2-s2.0-25144518343 (Scopus ID)
Note
QC 20100813Available from: 2008-04-04 Created: 2008-04-04 Last updated: 2015-03-30Bibliographically approved
3. Noncollinear double-ring optical parametric oscillators with periodically poled KTiOPO
Open this publication in new window or tab >>Noncollinear double-ring optical parametric oscillators with periodically poled KTiOPO
2004 (English)In: Optics Express, ISSN 1094-4087, Vol. 12, 5526- p.Article in journal (Refereed) Published
Abstract [en]

A pulsed self-seeded double-ring optical parametric oscillatorrealized with periodically poled KTiOPO4 is demonstrated. When pumpedfrom two opposite directions, the cavity supported two automaticallyaligned, independent, counter-propagating parametric wave pairs whosewavelength could be continuously tuned by varying a single degree offreedom. The tuning range from 1189 nm to 1267 nm has been achieved forthe resonant idler waves. The parametric rings could be cross-seeded byusing a feedback arrangement. Here, Fourier-domain filtering was utilizedto spectrally manipulate the output spectrum of the seeded ring oscillator.Parametric ring oscillator efficiencies of 46 % were achieved.

Keyword
Feedback, Light amplifiers, Nonlinear optics, Optical fibers, Optical systems, Potassium compounds, Signal processing, Wave propagation
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-5899 (URN)10.1364/OPEX.12.005526 (DOI)000224867400026 ()2-s2.0-10444235759 (Scopus ID)
Note
QC 20100923 QC 20110914Available from: 2006-06-01 Created: 2006-06-01 Last updated: 2015-03-30Bibliographically approved
4. Two-dimensional quasi-phase-matched multiplecascaded four-wave mixing in periodically poled KTiOPO
Open this publication in new window or tab >>Two-dimensional quasi-phase-matched multiplecascaded four-wave mixing in periodically poled KTiOPO
2006 (English)In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 31, no 22, 3324-3326 p.Article in journal (Refereed) Published
Abstract [en]

A two-dimensional quasi-phase-matched structure is realized in a noncollinear, nondegenerate periodically poled KTiOPO4 parametric oscillator by utilizing the mutual coherence of two noncollinear pump beams. The mutually coherent pump beams form an interference pattern inside the crystal that is directed perpendicular to the existing quasi-phase-matched grating vector and acts as a parametric gain grating. The cavity itself supports two signal wavelengths around 1550 nm with tunable separation, while the gain grating reduces the operational threshold of the oscillator. Furthermore, with this two-dimensional quasi-phasematched structure, we can demonstrate the generation of new spectral components through multiple chi((2)) : chi((2))-caseaded four-wave mixing processes.

Keyword
optical parametric oscillator, nonlinear photonic crystal, amplifier
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-5900 (URN)10.1364/OL.31.003324 (DOI)000241799700035 ()2-s2.0-33845533036 (Scopus ID)
Note
Uppdaterad från submitted till published: 20100923. QC 20100923Available from: 2006-06-01 Created: 2006-06-01 Last updated: 2011-10-03Bibliographically approved
5. Ultrabroad Gain in an Optical Parametric Generator with periodically poled KTiOPO4
Open this publication in new window or tab >>Ultrabroad Gain in an Optical Parametric Generator with periodically poled KTiOPO4
Show others...
2006 (English)In: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 85, no 1, 73-77 p.Article in journal (Refereed) Published
Abstract [en]

An optical parametric gain bandwidth of 115 THz at full-width half maximum is generated from a picosecond Ti:sapphire pumped degenerate optical parametric generator. This ultrabroad bandwidth could be obtained by first identifying the wavelength where the nonlinear optical material has zero group-velocity dispersion (GVD). By pumping at half this wavelength the degenerate signal-idler pairs can accommodate ultrabroad bandwidths. The explanation for this is that the group velocities of the signal and the idlers are approximately matched and the GVD is small. However, in order to thoroughly investigate the degeneracy region around 1700 nm we fabricated several periodically poled KTiOPO4 (PPKTP) crystals with different periods, and also one periodically poled RbTiOPO4 (PPRTP). Both collinear and noncollinear configurations were employed for broadband parametric generation in this region. It was found that the optimum pump wavelength is in the region between 800 nm to 850 nm for PPKTP, and we could also conclude that a similar performance was found for PPRTP. This work will allow the design of optical parametric devices for generating few-cycle pulses in the spectral region between 1.1 mu m and 3.8 mu m.

Keyword
laser fields, amplification, oscillator, pulses, ktp, energy, power
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-5901 (URN)10.1007/s00340-006-2253-7 (DOI)000240519300014 ()2-s2.0-33748708651 (Scopus ID)
Note
QC 20100923Available from: 2006-06-01 Created: 2006-06-01 Last updated: 2015-03-30Bibliographically approved
6. Broadly Tunable Picosecond Narrowband pulses in a periodically poled KTiOPO4 parametric amplifier
Open this publication in new window or tab >>Broadly Tunable Picosecond Narrowband pulses in a periodically poled KTiOPO4 parametric amplifier
2006 (English)In: Optics Express, ISSN 1094-4087, Vol. 14, no 19, 8728-8739 p.Article in journal (Refereed) Published
Abstract [en]

A picosecond double-pass periodically poled KTiOPO4 (PPKTP) noncollinear parametric amplifier that delivers tunable and narrowband outputs between 1.1 mu m and 1.65 mu m is reported. The seed source is an ultra-broadband emitting PPKTP collinear parametric generator, which is spectrally narrowed, from a bandwidth of 80 THz to about 0.3 THz, by a Fourier-filtering arrangement. A parametric gain of 70 dB is measured with preserved spectral bandwidth, resulting in a signal energy of 6.5 mu J at a pump energy of 60 mu J from the Ti:sapphire regenerative amplifier. The total energy-budget for the setup is less than 100 mu J with an optical-to-optical efficiency of 12%. This particular system is scalable to even lower pump energies by tighter focusing arrangements

Keyword
raman scattering microscopy, high-sensitivity, amplification, diode
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-5902 (URN)10.1364/OE.14.008728 (DOI)000240638700030 ()2-s2.0-33748928629 (Scopus ID)
Note
Uppdaterad från submitted till published: 20100923. QC 20100923Available from: 2006-06-01 Created: 2006-06-01 Last updated: 2015-03-30Bibliographically approved
7. Tailored UV-laser source for fluorescence spectroscopy of biomolecules
Open this publication in new window or tab >>Tailored UV-laser source for fluorescence spectroscopy of biomolecules
2007 (English)In: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 45, no 4, 444-449 p.Article in journal (Refereed) Published
Abstract [en]

A dual-wavelength UV-laser source was developed for biosensing. First, a passively Q-switched diode-pumped Nd:YAG laser was constructed. The astigmatic diode output beam was converted into a homogenous beam profile by utilizing a mode converter. As a result, a frequency-doubling conversion efficiency of 50% was achieved in a periodically poled KTiOPO4. With a repetition rate of 100 Hz, the pulse energies and lengths were 650 mu J and 1.8 ns, respectively, at 532 nm with a M-2 of 1.3. The UV-generation is based on cascaded parametric processes using an intra-cavity sum-frequency mixing scheme in a periodically poled KTiOPO4 parametric oscillator pumped at 532 nm. Here, the wavelengths 293 and 343 nm were generated, with conversion efficiencies of 7% and 6.5%, respectively, in respect to 532 nm. With pulse length 1 ns and an average power above 2.7 mW, the wavelengths were used for fluorescence measurements of nonpathogenic bacteria.

Keyword
diode pump solid-state laser, beam transformation, beam shaping, optical parametric oscillator, parametric devices, ultraviolet generation
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-5903 (URN)10.1016/j.optlaseng.2005.03.016 (DOI)000245108800002 ()
Note
QC 20100923Available from: 2006-06-01 Created: 2006-06-01 Last updated: 2015-03-30Bibliographically approved

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