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Dynamics of green light-induced infrared absorption in KTiOPO4 and periodically poled KTiOPO4
KTH, Superseded Departments, Physics.
KTH, Superseded Departments, Physics.ORCID iD: 0000-0002-2508-391X
KTH, Superseded Departments, Physics.ORCID iD: 0000-0001-7688-1367
2004 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 96, no 4, 2023-2028 p.Article in journal (Refereed) Published
Abstract [en]

Induced thermal-lens spectroscopy with a common-path interferometer has been used for high-sensitivity measurements of green-light induced absorption dynamics in single-domain and periodically poled KTiOPO4. Although the linear infrared absorption in both materials is the same, the saturated green-light induced absorption is consistently higher in periodically poled crystals. Initial relaxation of the induced absorption is also different in these materials where periodically poled KTP does not exhibit as fast initial relaxation characteristic as the single domain KTP. These differences in the absorption are explained by higher concentration of native defects associated with weakly bonded K+ ions, which stabilize electron and hole traps forming color centers in the material. Unannealed as-poled crystals also exhibit characteristic overshoot dynamics in the induced thermal lens signal, which signifies remnant stress in the domain walls. Investigations showed that the lattice vibration energy generated by the dissociation of induced color centers is sufficient for complete relaxation of this remaining stress. The sensitivity of the measurement technique is demonstrated by the measurement of small signal absorption in the blue spectral region arising during continuous wave quasi-phase-matched second harmonic generation in periodically poled KTP.

Place, publisher, year, edition, pages
2004. Vol. 96, no 4, 2023-2028 p.
Keyword [en]
flux-grown ktiopo4, gray tracks, high-power, ktp, laser, generation, radiation, crystals, nm
National Category
Physical Sciences
URN: urn:nbn:se:kth:diva-8757DOI: 10.1063/1.1738528ISI: 000223055100038ScopusID: 2-s2.0-4344717095OAI: diva2:14167
QC 20110211Available from: 2005-11-09 Created: 2005-11-09 Last updated: 2015-03-30Bibliographically approved
In thesis
1. Fabrication and characterization of periodically poled KTB and RB-doped KTB for applications in the visible and UV
Open this publication in new window or tab >>Fabrication and characterization of periodically poled KTB and RB-doped KTB for applications in the visible and UV
2005 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This thesis deals with the fabrication and the characterization of periodically-poled crystals for use in lasers to generate visible and UV radiation by second-harmonic generation (SHG) through quasi-phasematching (QPM). Such lasers are of practical importance in many applications like high-density optical storage, biomedical instrumentation, colour printing, and for laser displays.

The main goals of this work were: (1) to develop effective monitoring methods for poling of crystals from the KTiOPO4 (KTP) family, (2) to develop useful non-destructive domain characterization techniques, (3) to try to find alternative crystals to KTP for easier, periodic poling, (4) to investigate the physical mechanisms responsible for optical damage in KTP. The work shows that the in-situ SHG technique used together with electro-optic monitoring, makes it possible to obtain reliable, real-time information regarding the poling quality over the whole crystal aperture during the electric-field poling process. Using this combined monitoring method, both KTP and Rb-doped KTP (RKTP) crystals were successfully poled. By comparing these two crystals, we found that a low-doped KTP has a substantially reduced ionic conductivity and, thus, a high-quality periodic poling can be obtained without otherwise affecting the properties of the crystal. RKTP is a good alternative candidate to KTP for poling purpose. We have also shown that Atomic Force Microscopy (AFM) is an informative tool for investigating domain nucleation, growth, and merging. Furthermore, we have demonstrated a simple technique for 3D characterization of QPM samples. It utilizes a group-velocity mismatched, type-II SHG of femtosecond pulses for layer-by-layer monitoring of the effective nonlinearity along the propagation direction of the beam. The quality of these crystals was finally reflected in a number of SHG experiments with a variety of laser sources. High energies and high efficiencies were thus demonstrated using CW, mode-locked and Q-switched lasers. Gratings with pitches smaller than 3 µm, were demonstrated for first-order UV generation. Type-II QPM SHG was demonstrated as a technique for reducing the fabrication constraints.

High intensity light in the visible and the UV leads to modification of the material properties and, eventually, to optical damage. In KTP and its isomorphs, the first sign of material change is an optically-induced absorption. We have used thermal-lens spectroscopy with a common-path interferometer for high-sensitivity measurements of green light-induced infrared absorption dynamics in single-domain and periodically-poled KTP (PPKTP). The saturated, green light-induced absorption has been shown to be consistently higher in periodically-poled crystals, and is attributed to the creation of stoichiometric and interstitial defects in the crystals during the poling process. Finally, irreversible bulk damage thresholds in PPKTP have been determined for pulsed frequency converters. As the characteristics of optical damage are closely related to the material quality, this investigation can provide useful information for crystal manufactures and will help to optimise the crystal growth conditions.

Trita-FYS, ISSN 0280-316X ; 2005:50
Nonlinear optics, second-harmonic generation, quasi-phasematching, type-I QPM SHG, type-II QPM SHG, KTP, RKTP, periodic electric-field poling
National Category
Physical Sciences
urn:nbn:se:kth:diva-483 (URN)91-7178-153-6 (ISBN)
Public defence
2005-11-25, Sal FB53, AlbaNova, Roslagstullsbacken 21, Stockholm, 10:00
Available from: 2005-11-09 Created: 2005-11-09 Last updated: 2012-03-22

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