Passive Optical Shutters
Passive Q-Switching and Mode-Locking of 1.3-3 mkm Lasers: New Materials and Technologies
Tech Area / Field
- PHY-OPL/Optics and Lasers/Physics
3 Approved without Funding
Belorussian State Polytechnic Academy / International Laser Center, Belarus, Minsk
- Solix, Belarus, Minsk\nInstitute of General Physics named after A.M. Prokhorov RAS / Laser Materials and Technology Research Center, Russia, Moscow\nScientific-Practical Materials Research Centre NAS of Belarus, Belarus, Minsk\nSt Petersburg State Polytechnical University, Russia, St Petersburg
- Airbus Deutschland GmbH, Germany, Munich\nRoyal Institute of Technology / Laser Physics and Quantum Optics, Sweden, Stockholm\nUniversity of Southampton / Optoelectronics Research Center, UK, Southampton\nUniversität Hamburg / Institut für Laser Physik, Germany, Hamburg
Project summaryThe goals of the project are:
- to develop methods of synthesis and to investigate new materials including single crystals (ZnSe, CdMnTe, MgAl2O4, Y3Al5O12) doped with tetrahedrally co-ordinated transition metal ions (Co2+, Fe2+, V3+) and semiconductor (PbS and PbSe)-doped glasses for passive Q-switching and mode-locking of fibre and diode-pumped solid-state lasers emitting in the 1.3–3 mm wavelength region;
- to compare the Q-switch performance of new passive shutters with that of new active shutters based on Frustrated Total Internal Reflection.
The state of the art in the field of researches. There is currently significant interest in optical shutters for spectral region from 1.3 to 3 micron. Solid state lasers emitting in this region are widely used for LIDAR applications, telecommunications, various therapeutic and surgical applications. A lot of these applications require reliable, simple and compact laser systems with short and powerful laser pulses. In this connection, techniques of passive Q-switching and mode-locking are both compact and simple because they need only a saturable absorber (passive shutter) introduced in the laser cavity, without any auxiliary electronics.
The promising types of passive shutters for solid-state lasers of 1.3-3 mm wavelength range are single crystals doped with tetrahedrally coordinated transition metal ions and IV-VI semiconductor-doped glasses. Tetrahedral sites lack inversion symmetry, providing the odd-parity field that is necessary to relax parity-selection rule, which results in high absorption cross sections for the transition metal ions. The use of different transition metal ions (V3+, Fe2+, Co2+, et. al.) is expected to cover the spectral range of saturable absorption from 1.3 up to 3 mm. The use of different host crystals (halcogenides, oxides) would enable to vary relaxation times of absorbers from microsecond to nano- and picosecond time domain and therefore to achieve both Q-switching and mode-locking regimes in lasers.
Another type of materials IV-VI semiconductor-doped glasses are perspective as solid-state saturable absorbers due to strong quantum-confinement in small semiconductor crystals of nanometer sizes (nanocrystals) causes a large nanocrystals size-depending short-wavelength shift of the absorption edge with respect to the bulk band gap. So that using of one semiconductor material (PbS or PbSe) allows to create passive shutters for different wavelengths across a wide spectral region of 1.3-3 micron (only a variation in the size of the nanocrystals is needed). Ultrafast bleaching relaxation times of such glasses would permit to obtain ultrashort pulses from solid-state lasers emitting in the near IR region.
On the other hand, active Q-switching of lasers is also thoroughly studied and widely used. Active modulators are typically much more complicated devices, which need additional high speed and power consumable electronics. However, in general active modulators produce higher pulse energies then passive ones primarily due to lower losses. From this point of view it is important to compare Q-switch laser performance obtained by means of passive shutters with those obtained by use of active modulators. The most perspective active Q-switches for solid-state lasers of 1.3-3 mm wavelength range are piezo-driven devices: Frustrated Total Internal Reflection (FTIR) optical shutters. The FTIR shutters have low driving voltage in comparison with electro-optical shutter. The FTIR-based Q-switches can be electrically tuned to an optimal laser outcoupling. Due to low losses FTIR shutters allows efficient Q-switching of low gain lasers.
The impact of the proposed project on the progress in the field of researches. Preparation of halcogenides (ZnSe, CdMnTe) and oxide (MgAl2O4, Y3Al5O12) single crystals doped with different tetrahedral transition metal ions (V3+, Co2+, Fe2+), semiconductor-doped glasses doped with PbS and PbSe nanocrystals of different size as well as spectroscopic investigations of their linear and nonlinear optical properties will allow to develop the saturable absorbers for Q-switching and mode-locking of fibre and diode-pumped solid-state lasers emitting in the 1.3-3 mm region.
Study of optical absorption, luminescence, and nonlinear absorption properties will allows to obtain novel scientific information about nonlinear phenomena and spectroscopic characteristics of tetrahedral transition metal (Co2+, Fe2+, V3+) ions in single crystals and IV-VI semiconductor nanocrystals in glasses.
The development of active shutters based on Frustrated Total Internal Reflection allows to compare the Q-switch performance of elaborated passive and active modulators and to choose the better one for each solid-state laser.
New passive shutters developed in frames of the proposed project will enable to produce compact and microchip lasers as well as Q-switched and mode-locked fibre lasers at different wavelengths in the infrared using simple and reliable methods of passive Q-switching and mode-locking.
Project teams. International Laser Center (ILC) is specialized in development of new laser materials and saturable absorber Q-switches and mode-lockers for solid-state lasers. One of the main research activities of this Group is conventional and nonlinear spectroscopy and laser investigations of transition metal-doped crystals and semiconductor-doped glasses. Institute of Solid State and Semiconductor Physics (ISSSP) of National Academy of Sciencies of Belarus is material-growth-oriented team with great experience in the field of II-VI and IV-VI chalcogenides compounds growth and in preparation of semiconductor structures and IR-devices for special applications based on these structures. Science and Production Company “SOLIX Ltd.” (SOLIX) has a great experience in the field of growing of oxide single crystals doped with rare-earth- and transition-metal ions for solid-state tunable lasers, namely Ti:sapphire, Cr:forsterite, alexandrite, Nd:YVO4, etc. St.-Petersburg State Polytechnical University (SPSPU) is specialized in preparing of semiconductor-doped oxide glasses and their characterization by X-ray diffraction, chemical etching, and transmission electron microscopy. This team has a great experience in the field of II-VI and IV-VI chalcogenides compound-doped glasses preparing. Laser Materials and Technologies Research Center (LMTRC) of General Physics Institute of Russian Academy of Sciences has great experience in research and development of solid-state active and passive laser materials and lasers on their base. The fundamental investigation of energy excitation and relaxation processes in rare-earth-ion doped laser crystals and glasses allowed the scientists of this group to develop new highly efficient erbium laser glasses.
Expected Results and their Application. The methods of synthesis of tetrahedrally co-ordinated V3+-doped yttrium aluminium garnet single crystal, tetrahedrally co-ordinated Co2+-doped magnesium aluminum spinel and Co2+ and Fe2+-doped zinc selenide and cadmium magnesium telluride single crystals as well as PbS, PbSe semiconductor-doped glasses will be elaborated, their spectroscopic and nonlinear optical properties at different wavelengths will be characterized. Ultimately, passive Q-switches and mode-lockers based on these materials will be elaborated for various 1.3-3 mm fibre and diode-pumped solid-state lasers, and their Q-switch performance will be compared with Q-switch operation of new Frustrated Total Internal Reflection active shutters.
The Project meets following ISTC Goals:
– The project execution could provide 27 weapon scientists and engineers from CIS state an opportunity to redirect their talents to peaceful activities: investigation of passive and active optical shutter materials for public applications.
– Integration of scientists from CIS into the international optical community, especially in European scientific community, will be strengthened due to extension of long-term collaboration with Institute for Laser Physics of Hamburg University (Germany), Optoelectronics Research Center of University of Southampton (United Kingdom), Corporate Research Center Germany of EADS (Germany), and Royal Institute of Technology of Stockholm University (Sweden).
– Applied research and technology development for peaceful purposes in the field of new types of passive and active optical shutters (based on impurity ions-doped crystals and semiconductor-doped glasses) for 1.3-3-micron lasers finding an application for medicine, telecommunication, etc.
– The project will contribute to the solution of international technical problem: development of solid state passive and active shutters for laser light sources tunable in the NIR- and mid-IR spectral range.
– The transition to market-based economy responsive to civil needs will be reinforced since the results open new opportunities for optical companies to arrange mass commercial production of laser components and equipment for public applications.
Scope of Activities. The project will be executed during 3 years by 51 persons of scientists and engineers from participating institutions. The activities of the project are pided into nine Tasks.
The goal of Task 1 is to elaborate the methods of preparation of Co2+-doped Cd1-xMnxTe, Co2+-doped ZnSe, and Fe2+-doped ZnSe single crystals with adequate optical quality (participating Institution - ISSSP).
The purpose of Task 2 is to elaborate the methods of preparation of Co2+-doped MgAl2O4 and V3+-doped Y3Al5O12 single crystals with trivalent vanadium and palent cobalt ions in tetrahedral sites having adequate optical quality (SOLIX).
The goal of Task 3 is the design and the synthesis of new glasses with low intrinsic optical absorption in spectral range 1.3-3 micron, the glass must allow embedding with narrowly size-distributed PbS(Se)-semiconductor nanocrystals having excitonic absorption maxima in the same spectral range and demonstrating the saturation of optical absorption under optical irradiation in the excitonic peak region (SPSPU).
The objective of Task 4 is detailed spectroscopic (including linear and nonlinear properties) characterization of the Co2+-doped ZnSe, Cd1-xMnxTe, and MgAl2O4, Fe2+-doped ZnSe, V3+-doped Y3Al5O12 crystals and PbS(Se)-doped glasses and optimization of the optical parameters of these crystals and glasses. At this stage the conditions of crystals and glasses growth will be corrected (in accordance with Tasks 1-3) in order to produce these materials with adequate optical and spectroscopic properties (ILC).
The goal of Task 5 is to characterize and optimize Q-switch performance of Co2+-doped MgAl2O4 (grown by different techniques), V3+-doped Y3Al5O12 crystals and PbS(Se)-doped glasses and mode-locker performance of PbS(Se)-doped glasses in diode-pumped 1.3-mm neodymium lasers (ILC).
The objective of Task 6 is to characterize and optimize Q-switch performance of Co2+-doped ZnSe and MgAl2O4 crystals, and PbS(Se)-doped glasses in diode-pumped 1.5-mm Er:glass and Er-doped fibre lasers, and mode-locker performance of PbS(Se)-doped glasses in 1.5-mm Er-doped fiber laser (ILC).
The purpose of Task 7 is to characterize and optimize Q-switch performance of Co2+-doped CdMnTe crystals and PbS(Se) -doped glasses in diode-pumped 2-mm Tm:Y3Al5O12 and Tm-doped fibre lasers, and mode-locker performance of PbS(Se)-doped glasses in 2-mm Tm-doped fiber laser (ILC).
The objective of Task 8 is to characterize and optimize Q-switch performance of Co2+-doped ZnSe and Fe2+-doped ZnSe crystals and PbS(Se)-doped glasses in diode-pumped 3-mm Er:YLiF4 laser (ILC).
The goal of Task 9 is to develop and optimize Frustrated Total Internal Reflection (FTIR)-based devices for implementation as Q-switches in solid-state lasers emitting at wavelengths of 1.3 mm (Nd-doped garnets), 1.5 mm (Er:glass), 2 mm (Ho:Y3Al5O12), and 3 mm (Er:Y3Al5O12) and to compare the Q-switch performance of the FTIR with that of elaborated (under Tasks 1-8) passive shutters (LMTRC).
Role of Foreign Collaborators. The project represents an international high-technology collaborative effort. Following collaborators intend to participate in the project implementation: (i) Institute for Laser Physics of Hamburg University (Germany) places at the disposal laser equipment for joint experiments on testing materials under investigation as passive shutters in diode-pumped 2-micron thulium and 3-micron erbium crystalline lasers; (ii) Optoelectronics Research Center of University of Southampton (United Kingdom) places at the disposal facilities to carry out joint experiments on passive Q-switching and mode-locking of 1.5-micron Er-doped and 2-micron Tm-doped fibre lasers; (iii) In collaboration with the Corporate Research Center Germany of EADS (Germany), joint experiments on passive Q-switching of compact diode-pumped 1.3-micron neodymium laser will be carried out; (iv) In collaboration with the Royal Institute of Technology of Stockholm University (Sweden), joint experiments on passive Q-switching of compact diode-pumped 1.5-micron Er-glass laser will be performed.
Technical Approach and Methodology. Task 1. Transition-metal-doped chalcogenides crystals will be prepared by using a two stage process. At the first stage undoped chalcogenides single crystals of high optical quality will be grown by sublimation traveling heater method or by Bridgman method. At the second stage the introduction of the cobalt or iron impurity into the host material will be performed by the solid phase metallic source diffusion process. Task 2. Co2+:MgAl2O4 and V3+:Y3Al5O12 crystals of high quality will be grown by Czochralski method. Elaboration of this method will consist of the theoretical grounds of a preparation methods, engineering of thermal schemes of technological process, examination of optimum crystals growth condition, elaboration of crystals annealing condition. Task 3. Synthesis mode of phosphate based oxide glasses will be chosen to prepare samples of virgin and semiconductor-doped glasses transparent in the spectrum range of 1.3-3 micron. Secondary thermal treatment of the glasses will be used to initiate phase decomposition of the glass-semiconductor system. Optimization of the treatment mode will allow to prepare semiconductor-doped glasses with necessary optical properties. Task 4. Spectroscopic measurements will be performed using standard absorption and luminescence technique. Nonlinear optical properties will be investigated using picosecond and nanosecond pump-probe technique and intensity- and energy-fluence-dependent transmission measurements. Computer simulation will be accomplished for the modeling of the experimental data on nonlinear transmission. Tasks 5-8. Q-switch characterization of activated crystals and glasses will be carried out using diode-pumped 1.3-mm neodymium-doped crystalline lasers, 1.5-mm Er:glass and Er-doped fibre lasers, 2-mm Tm:Y3Al5O12 and Tm-doped fibre lasers, and 3-mm Er-YLiF4 laser. Mode-locker characterization will be perform using diode-pumped 1.3-mm neodymium-doped crystalline lasers, 1.5-mm Er-doped fibre laser, and 2-mm Tm-doped fibre laser. Longitudinal diode-pumping of the lasers will be applied. Computer simulation of the Q-switching will be performed to compare the experimental and theoretical results. Following parameters of the Q-switches will be optimized: small-signal transmission, thickness, absorbing center size and concentration. Task 9. Technical approach is based on investigations of dynamic properties of lasers with Frustrated Total Internal Reflection (FTIR) shutters. The experiments will be carried out using 1.3-mm Nd-doped garnets, 1.5-mm Er:glass, 2-mm Ho:Y3Al5O12, and 3-mm Er:Y3Al5O12 lasers. Theoretical modeling of Q-switch regimes will be performed taking into consideration different lasing schemes (4-, 3-level schemes, and self restricted transitions). Q-switch performance of the FTIR shutters will be compared with that of passive shutters (elaborated under Tasks 1-8).