CN102074886A - Crystal orientation selected polarization state controllable microchip laser - Google Patents
Crystal orientation selected polarization state controllable microchip laser Download PDFInfo
- Publication number
- CN102074886A CN102074886A CN 201010590997 CN201010590997A CN102074886A CN 102074886 A CN102074886 A CN 102074886A CN 201010590997 CN201010590997 CN 201010590997 CN 201010590997 A CN201010590997 A CN 201010590997A CN 102074886 A CN102074886 A CN 102074886A
- Authority
- CN
- China
- Prior art keywords
- laser
- crystal
- yag crystal
- yag
- polarization state
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
Images
Abstract
The invention provides a crystal orientation selected polarization state controllable microchip laser, relating to a laser. The laser is provided with a pumping source, an isolator, a first lenticular lens, a second lenticular lens and a Yb:YAG crystal, wherein the pumping source adopts a 940nm laser diode; the isolator, the first lenticular lens, the second lenticular lens and the Yb:YAG crystal are arranged on an output laser optical axis of the pumping source in sequence; a 940nm anti-reflection film and a 1030nm highly reflective film are coated on the rear surface of the Yb:YAG crystal and the rear surface serves as the rear cavity surface of the microchip laser; the reflectivity of the highly reflective film is more than 99%; and a 1030nm partial transmission film and a 940nm anti-reflection film are coated on the front surface of the Yb:YAG crystal and the front surface serves as the front cavity mirror of the laser. The laser can obtain higher brightness and power than the original polarization state selection technology and the output laser can have purer polarization state.
Description
Technical field
The present invention relates to a kind of laser, especially relate to a kind of crystal orientation and select the controlled micro-slice laser of polarization state.
Background technology
Rare-earth-ion-doped yag crystal (Y
3Al
5O
12Be YAG) in current solid state laser field in occupation of critical role, particularly the Yb:YAG crystal has fluorescence lifetime, high-dopant concentration and the high quantum efficiency of wide absorption band, length, and under identical pump power, the heat that the Yb:YAG pumping produces only is 1/3rd of Nd:YAG.Adopt the bar-shaped laser of end pumping, profile pump and thin-sheet laser to obtain kilowatt even tens kilowatts continuous laser output.The Yb:YAG crystal of high-dopant concentration is fit to the development of micro-slice laser very much, realized the laser output of subnanosecond, peak power based on passive Q-adjusted Yb:YAG micro-slice laser, so the Yb:YAG crystal is subjected to increasing attention in field of lasers up to hundred kilowatts.
Because the YAG crystal belongs to cubic system, on spectrum, do not have picture YVO
4The polarization spectrum characteristic that crystal is the same, thus the output of its polarization laser mainly is to obtain linearly polarized laser output, apply external force realize the output of linearly polarized laser as the stress distribution that changes crystal or the temperature that changes crystal or adopt measure such as linear polarization pump light source to realize on crystal by the vibration that increases optical element such as polarizer or wave plate in the laser cavity or adopt the complicated cavity structure that the Brewster window is arranged to suppress a polarization state.So, not only make complex structure, the cost height, difficult in maintenance of laser, and the loss that also can bring into along with the increase of optical element of the efficient of laser and reducing.Another method commonly used is to adopt integrated optical element to realize linearly polarized laser output or add the photon crystal grating mirror with high polarization selectivity realizing the output of radial polarisation laser as form measures such as resonant grating mirror by the particular design plated film, yet this method to plated film require high, and owing between film and substrate, have stress, damage easily, be not suitable for high power operation.
Show by analysis and research, when rare earth ion replaces Y rare-earth ion-doped YAG crystal spectrum and crystalline field
3+During dodecahedron case that ion occupies, isotropic symmetry of YAG crystal is just broken, at D
2The symmetry of case Doped Rare Earth ion has reduced, even belongs to symmetry three times.Because the local anisotropy spectral characteristic that the crystal symmetry reduction is caused at rare-earth ion-doped YAG crystal such as Er, has obtained the confirmation of experiment among Yb:YAG and the Ho:YAG etc.Cr at doped transition metal ions
4+: also there are crystal-orientation-dependent saturable absorption characteristic ([14] H.Eilers, K.R.Hoffman, W.M.Dennis, S.M.Jacobsen, and W.M.Yen, " Saturation of 1.064 μ m absorption inCr, Ca:Y in the YAG crystal
3Al
5O
12Crystals, " Appl.Phys.Lett.61,2958-2960 (1992)).Adopt linear polarization pump light source pumping＜111〉direction Nd:YAG crystal to obtain linearly polarized laser output ([15] R.Dalgliesh, A.D.May, and G.Stephan, " Polarization states of a single-mode (microchip) Nd
3+: YAG laser-Part II:comparison oftheory andexperiment, " IEEE J.Quantum Electron.34,1493-1502 (1998)).Adopt the Nd:YAG crystal of＜100〉direction cuttings to obtain two-way polarization laser output ([16] A.M as gain medium
cKay, J.M.Dawes, and J.Park, " Polarisation-mode coupling in (100)-cut Nd:YAG, " Opt.Express 15,16342-16347 (2007)).These Nd:YAG crystal orientations need linear polarization pumping source and special crystal-cut direction to the achievement in research of linearly polarized laser, make that not only laser costs an arm and a leg, and be not suitable for tradition＜111 Nd:YAG or the application of Yb:YAG crystal in micro-slice laser of direction growth.Utilize doping with rare-earth ions YAG crystal self local anisotropy optical property, with the Yb:YAG crystal of function admirable as gain medium, by selecting the polarization state that suitable crystal orientation is controlled output laser in (111) crystal face, in laser diode-pumped microplate solid state laser, not only can realize high light beam quality, the output of high efficiency laser; And in laser diode-pumped＜111〉obtained crystal orientation in the direction Yb:YAG crystal micro-chip laser first from linearly polarized laser output ([17] J.Dong that selects, A.Shirakawa, and K.Ueda, " A crystalline-orientationself-selected linearly polarized Yb:Y
3Al
5O
12Microchip laser, " Appl.Phys.Lett.93,101105 (2008)).We discover, have six special directions in Yb:YAG (111) crystal face, can obtain extinction ratio and export greater than 100 linearly polarized laser.Exist the phase relation of 90 ° and 30 ° between this six direction, be symmetric relation three times, with＜111 localised crystal's orientation of direction growth Yb:YAG crystal has tangible corresponding relation.This achievement in research has been broken traditional viewpoint, and promptly the Yb:YAG crystal belongs to cubic system, and optical spectra presents isotropism, need add optical element usually or apply external force to realize linearly polarized laser output.Further widen the application of Yb:YAG crystal in high power solid wires polarization laser, promote laser diode-pumped high power, different polarization states microplate solid state laser competitiveness.Simultaneously also for adopting traditional rare-earth ion-doped YAG laser crystal to provide a more convenient and succinct approach from selecting to obtain the controlled laser output of polarization state by crystal orientation, can simplify production procedure greatly, thereby have very important theory and realistic meaning.
Summary of the invention
The object of the present invention is to provide a kind of crystal orientation to select the controlled micro-slice laser of polarization state.
Described crystal orientation selects the controlled micro-slice laser of polarization state to be provided with pumping source, isolator, the 1st lens pillar, the 2nd lens pillar and Yb:YAG crystal; Described pumping source adopts the 940nm laser diode, isolator, the 1st lens pillar, the 2nd lens pillar and Yb:YAG crystal are located on the output laser beam axis of pumping source successively, the anti-reflection film of the rear surface plating 940nm of described Yb:YAG crystal and the high-reflecting film of 1030nm, rear facet as micro-slice laser, the anti-reflectivity of touching of described height is greater than 99%, and the part transmitting film of the front surface of described Yb:YAG crystal plating 1030nm and the anti-reflection film of 940nm are as the front cavity mirror of laser.
The laser of described laser diode output prevents the damage to laser diode of the pump light that reflects by isolator, be coupled and focus on the rear surface of pump light to the Yb:YAG crystal by two lens pillars.
The present invention utilizes in rare-earth ion-doped YAG crystal, when rare earth ion replaces Y
3+During dodecahedron case that ion occupies, isotropic symmetry of YAG crystal is just broken, at D
2The symmetry of case Doped Rare Earth ion presents 3 subsymmetric crystal structure characteristics and the local anisotropy optical characteristics that caused is sought a kind of convenience, the succinct controlled microplate Solid State Laser new technology of laser polarization state.
Key technology of the present invention is at first to adopt X-ray direction finder to determine that in rare-earth ion-doped YAG crystal (111) crystal face six special low index crystal orientation indexes are as＜011〉and＜211, select suitable crystal orientation by rotation Yb:YAG crystal, thereby can realize laser in different polarization states output easily.
Adopt laser diode-pumped crystal orientation to select the controlled microplate solid state laser of polarization state, the main rare-earth-ion-doped YAG crystal of using＜111〉direction growths are realized high electric light transformation efficiency, high light beam quality, high brightness, the controlled microplate solid state laser of polarization state as gain medium by selecting the interior different crystal orientation of (111) crystal face.
Compare with the existing technology that in micro-slice laser, obtains different polarization states, the present invention is owing to made full use of 3 symmetric crystal structure characteristics that form in the rare-earth ion-doped YAG crystal and the local anisotropy optical characteristics that is caused thereof, with commercial Yb:YAG crystal as gain medium, by selecting different crystal orientation in crystal (111) crystal face, do not needing additional any optics, under the situation of mechanical organ and external force, adopt commercial laser diode in the Yb:YAG micro-slice laser, to realize different polarization states (linear polarization as pumping source, elliptical polarization, circular polarization) 1030 or the output of the efficient laser of 1049nm, can make the miniaturization more of a whole set of Laser Devices, integrated and practicability.The laser material can adopt＜111〉the direction rare-earth-ion-doped YAG crystal (as the Yb:YAG crystal) of growing, adopt the mode of end pumping to make pump light and output laser coupled effectively, not only can obtain high light beam quality, the output of high optics transformation efficiency laser, and can realize the controlled microchip laser output of crystal orientation selection polarization state.So the present invention can obtain the brightness higher than original polarization state selection technology, higher power, and output laser can be realized purer polarization state.
Description of drawings
Fig. 1 is that the structure of the embodiment of the invention is formed schematic diagram.
Fig. 2 is Yb
3+The distribution of orientations that ion in the YAG cubic cell with respect to XYZ coordinate is and the distribution of orientations of 6 different case symmetries.
Fig. 3 is crystal orientation selection and the corresponding relation of exporting laser polarization state in (111) crystal face in the Yb:YAG crystal.Wherein there are 6 directions that may realize linearly polarized laser output, select different angle θ can realize elliptical polarization, circularly polarized laser output by rotating crystal.
Embodiment
Referring to Fig. 1, the described crystal orientation of the embodiment of the invention selects the controlled micro-slice laser of polarization state to be provided with pumping source 1, isolator the 2, the 1st lens pillar the 3, the 2nd lens pillar 4 and Yb:YAG crystal 5; Described pumping source 1 adopts the 940nm laser diode, isolator the 2, the 1st lens pillar the 3, the 2nd lens pillar 4 and Yb:YAG crystal 5 are located on the output laser beam axis of pumping source 1 successively, the anti-reflection film of the rear surface plating 940nm of described Yb:YAG crystal 5 and the high-reflecting film of 1030nm, rear facet 7 as micro-slice laser, the anti-reflectivity of touching of described height is greater than 99%, and the part transmitting film of the front surface of described Yb:YAG crystal plating 1030nm and the anti-reflection film of 940nm are as the front cavity mirror 6 of laser.
The laser of described laser diode output prevents the damage to laser diode of the pump light that reflects by isolator 2, be coupled and focus on the rear surface of pump light to the Yb:YAG crystal 5 by the 1st lens pillar 3 and 4 two lens pillars of the 2nd lens pillar.
The 940nm laser diode is as pumping source 1, pass through isolator 2 from the laser diode emitting laser, incident laser by isolator 2 compresses the fast axle angle of divergence of pump light through the 1st lens pillar 3, compresses the slow axis angle of divergence of laser diode with the 2nd lens pillar 4.Optical coupled by the 1st lens pillar 3 and the 2nd lens pillar 4 and focus on that to form an area on the plane of incidence of gain medium Yb:YAG crystal 5 be 50 * 50 μ m
2Pump spot; The anti-reflection film of the rear surface plating 940nm of Yb:YAG crystal 5 and the high-reflecting film of 1030nm are as the Effect of Back-Cavity Mirror 7 of laser cavity; The anti-reflection film of the front surface plating 940nm of Yb:YAG crystal 5 and the partial reflection film of 1030nm are as the Effect of Back-Cavity Mirror 6 of laser cavity.
The used gain medium of the present invention is with the high-quality Yb:YAG crystal of czochralski method (Czochralski) along＜111〉direction growths, is that the Yb:YAG crystal of 10at.% is that example illustrates content of the present invention with the doping content.
Below provide described crystal orientation and select the manufacture method of the controlled micro-slice laser of polarization state:
At first the doping content of high-quality be the Yb:YAG crystal-cut of 10at.% become to be of a size of the crystal blank of Ф 10 * 1.5mm, then to this crystal blank roughly grind, fine grinding and polishing, obtaining the optical parallel degree is the crystal microchip of 1mm less than 1/10 λ, thickness, then the crystal after the polishing is carried out plated film.The specific targets of plated film are as follows: in the face of the high-reflecting film of the anti-reflection film of the one side plating 940nm of the Yb:YAG crystal micro-chip of 940nm pump light incident and the 1030nm Effect of Back-Cavity Mirror as the micro-slice laser laser cavity, the secondary that the high-reflecting film that simultaneously plates 940nm in addition is used for reflected pump light and increases pump light absorbs, improve the light-phototranstormation efficiency of laser, the front cavity mirror of the partial reflection film formation laser of plating 1030nm (plates 90% reflectance coating usually and realizes 1030nm laser output efficiently on this face simultaneously; Plating realizes the laser output of 1049nm less than 5% transmitting film).As pumping source, obtaining diameter by the optical coupling system be made up of the condenser lens of two different focal at the plane of incidence of Yb:YAG crystal is the pump spot of 100 μ m with the laser diode of 940nm, improves the pattern matching of pump light and output laser.The power of output laser is measured by power meter, then is to test by rotating highly sensitive Glan-Thomson prism for the test of exporting laser polarization.It then is to realize by a rotatable mechanical device is installed on the Yb:YAG crystal that crystal orientation is selected the realization of the controlled laser of polarization state.(crystal orientation of＞10at.%) Yb:YAG crystal selects the controlled micro-slice laser of polarization state to determine the crystal thickness of its optimization according to its concrete doping content, thereby realizes that efficient laser exports based on high-dopant concentration for other.
The present invention utilizes in rare-earth ion-doped YAG crystal, when rare earth ion replaces Y
3+During dodecahedron case that ion occupies, isotropic symmetry of YAG crystal is just broken, at D
2The symmetry of case Doped Rare Earth ion presents 3 subsymmetric crystal structure characteristics (as shown in Figure 2) and the local anisotropy optical characteristics that caused is sought a kind of convenience, the succinct controlled microplate Solid State Laser new technology of laser polarization state.Each cuboid in Fig. 2 is represented the D of a local location
2The symmetry case, the position that has 6 different crystal orientations in the three assymetric crystal structures of Yb:YAG crystal, provided the local coordinate system (xyz) of two crystal orientations that are in position 1 and 2 among the figure, wherein the x-axle is along crystal [001] direction, the y-axle is along crystal [110] direction, and the z-axle is along crystal [110] direction.
Key technology of the present invention is at first to adopt X-ray direction finder to determine that in rare-earth ion-doped YAG crystal (111) crystal face 6 special low index crystal orientation indexes are as＜011〉and＜211, as shown in Figure 3.Select suitable crystal orientation by rotation Yb:YAG crystal, thereby can realize laser in different polarization states output easily.
6 linear polarization that the particular orientation correspondence may occur in Fig. 3; Select suitable angle θ by rotating crystal, can realize the output of elliptical polarization or circularly polarized laser.
Laser diode-pumped crystal orientation is selected the controlled microplate solid state laser of polarization state, being mainly concerned with usefulness＜111〉the rare-earth-ion-doped YAG crystal of direction growth is as gain medium, realizes high electric light transformation efficiency, high light beam quality, high brightness, the controlled microplate solid state laser of polarization state by selecting in (111) crystal face different crystal orientations.
Claims (1)
1. crystal orientation is selected the controlled micro-slice laser of polarization state, it is characterized in that being provided with pumping source, isolator, the 1st lens pillar, the 2nd lens pillar and Yb:YAG crystal; Described pumping source adopts the 940nm laser diode, isolator, the 1st lens pillar, the 2nd lens pillar and Yb:YAG crystal are located on the output laser beam axis of pumping source successively, the anti-reflection film of the rear surface plating 940nm of described Yb:YAG crystal and the high-reflecting film of 1030nm, rear facet as micro-slice laser, the anti-reflectivity of touching of described height is greater than 99%, and the part transmitting film of the front surface of described Yb:YAG crystal plating 1030nm and the anti-reflection film of 940nm are as the front cavity mirror of laser.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN 201010590997 CN102074886A (en) | 2010-12-15 | 2010-12-15 | Crystal orientation selected polarization state controllable microchip laser |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN 201010590997 CN102074886A (en) | 2010-12-15 | 2010-12-15 | Crystal orientation selected polarization state controllable microchip laser |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN102074886A true CN102074886A (en) | 2011-05-25 |
Family
ID=44033288
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN 201010590997 Pending CN102074886A (en) | 2010-12-15 | 2010-12-15 | Crystal orientation selected polarization state controllable microchip laser |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN102074886A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102263364A (en) * | 2011-06-17 | 2011-11-30 | 华北电力大学（保定） | Transverse plane pump laser capable of high efficiently using pump light |
| CN104810719A (en) * | 2015-05-22 | 2015-07-29 | 厦门大学 | IG (Ince-Gaussian) mode controllable neodymium-doped yttrium vanadate and chromium-doped yttrium aluminium garnet composite microchip laser |
| CN113363798A (en) * | 2021-05-20 | 2021-09-07 | 厦门大学 | Adjustable high-optical-efficiency broadband multi-longitudinal-mode Raman microchip laser |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6154479A (en) * | 1994-10-13 | 2000-11-28 | Nec Corporation | VCSELs (vertical-cavity surface emitting lasers) and VCSEL-based devices |
| CN101276126A (en) * | 2008-04-23 | 2008-10-01 | 清华大学 | Double Brewster's angle nonlinear optical crystal and cutting method thereof |
| CN101499608A (en) * | 2009-03-06 | 2009-08-05 | 北京交通大学 | Optically parametric oscillator |
| CN101521354A (en) * | 2009-04-08 | 2009-09-02 | 中国科学院长春光学精密机械与物理研究所 | Vertical cavity surface emitting laser (VCSEL) capable of controlling polarization direction |
-
2010
- 2010-12-15 CN CN 201010590997 patent/CN102074886A/en active Pending
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6154479A (en) * | 1994-10-13 | 2000-11-28 | Nec Corporation | VCSELs (vertical-cavity surface emitting lasers) and VCSEL-based devices |
| CN101276126A (en) * | 2008-04-23 | 2008-10-01 | 清华大学 | Double Brewster's angle nonlinear optical crystal and cutting method thereof |
| CN101499608A (en) * | 2009-03-06 | 2009-08-05 | 北京交通大学 | Optically parametric oscillator |
| CN101521354A (en) * | 2009-04-08 | 2009-09-02 | 中国科学院长春光学精密机械与物理研究所 | Vertical cavity surface emitting laser (VCSEL) capable of controlling polarization direction |
Non-Patent Citations (2)
| Title |
|---|
| 《Appl.Phys.Lett》 20080909 jun dong et.al. A crystalline-orientation self-selected linearly polarized Yb:Y3Al5o12 microchip laser 第93卷, * |
| 《中国激光》 20100930 董俊 等 被动调Q掺Yb3+激光材料固体微片激光器的研究进展 第37卷, 第9期 2 * |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102263364A (en) * | 2011-06-17 | 2011-11-30 | 华北电力大学（保定） | Transverse plane pump laser capable of high efficiently using pump light |
| CN102263364B (en) * | 2011-06-17 | 2012-11-21 | 华北电力大学（保定） | Transverse plane pump laser capable of high efficiently using pump light |
| CN104810719A (en) * | 2015-05-22 | 2015-07-29 | 厦门大学 | IG (Ince-Gaussian) mode controllable neodymium-doped yttrium vanadate and chromium-doped yttrium aluminium garnet composite microchip laser |
| CN113363798A (en) * | 2021-05-20 | 2021-09-07 | 厦门大学 | Adjustable high-optical-efficiency broadband multi-longitudinal-mode Raman microchip laser |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| JP2657525B2 (en) | Method and apparatus for generating coherent light radiation in a cavity by light mixing | |
| Chen et al. | 3.8 W of cw blue light generated by intracavity frequency doubling of a 946-nm Nd: YAG laser with LBO | |
| CN101950918B (en) | Self-frequency doubling green light solid-state laser suitable for laser display | |
| JP2007036195A (en) | Laser apparatus using nonlinear optical crystal or solid slab laser rod of multiplex optical path | |
| Jin et al. | Wideband tunable graphene-based passively Q-switched Tm: YAP laser | |
| US9658513B2 (en) | Device and method for converting a light and a laser system | |
| CN105958313A (en) | Laser pulse modulation device based on CrOCl crystal, and application thereof in all-solid-state laser | |
| CN105071217A (en) | Self-frequency-doubling all-solid-state yellow-light laser | |
| CN113381277A (en) | Circular polarization laser of chiral metamaterial | |
| CN102074886A (en) | Crystal orientation selected polarization state controllable microchip laser | |
| Xu et al. | InGaN-LD-pumped Pr3+: LiYF4 continuous-wave deep red lasers at 697.6 and 695.8 nm | |
| CN102025100B (en) | Single frequency visible laser based on self frequency doubling laser crystal | |
| CN102545027B (en) | Yb: YAG (yttrium aluminum garnet) and Cr, Yb: YAG self-Q-switching laser | |
| CN113594842A (en) | Device and method for generating ultrashort pulse of erbium-doped laser | |
| Liu et al. | High-beam-quality 2 μm tunable Tm: GdScO3 laser pumped by a 793 nm laser diode | |
| WO2020211333A1 (en) | Embedded crystal, preparation method therefor, and application thereof | |
| CN111041557A (en) | Thulium-holmium double-doped lutetium oxide laser crystal and growth method and application thereof | |
| Zhai et al. | A compact efficient deep ultraviolet laser at 266 nm | |
| Liu et al. | Tunable Pr3+: LiYF4 lasers in the green-red spectral region | |
| Wei et al. | A passively Q-switched YVO4 Raman laser with orthogonally polarized emission at 1175.4 nm and 1165.2 nm | |
| CN114784606A (en) | Laguerre Gaussian beam generating device and method | |
| Xu et al. | Single-and dual-wavelength laser operation of a diode-pumped Nd: LaF3 single crystal around 1.05 μm and 1.32 μm | |
| Shen et al. | A frequency-doubled Nd: YAG/KTP laser at 561 nm with diode side-pumping | |
| CN104466660A (en) | All-solid-state self-Raman tunable laser unit | |
| CN112421370A (en) | Self-frequency-doubling full-solid-state laser based on quasi-two-level laser radiation |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| C06 | Publication | ||
| PB01 | Publication | ||
| C10 | Entry into substantive examination | ||
| SE01 | Entry into force of request for substantive examination | ||
| C02 | Deemed withdrawal of patent application after publication (patent law 2001) | ||
| WD01 | Invention patent application deemed withdrawn after publication |
Application publication date: 20110525 |