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Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 21, Iss. 23 — Nov. 18, 2013
  • pp: 27697–27706
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Pump spot size dependent lasing threshold in organic semiconductor DFB lasers fabricated via nanograting transfer

Xin Liu, Sönke Klinkhammer, Ziyao Wang, Tobias Wienhold, Christoph Vannahme, Peter-Jürgen Jakobs, Andreas Bacher, Alban Muslija, Timo Mappes, and Uli Lemmer  »View Author Affiliations


Optics Express, Vol. 21, Issue 23, pp. 27697-27706 (2013)
http://dx.doi.org/10.1364/OE.21.027697


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Abstract

Optically excited organic semiconductor distributed feedback (DFB) lasers enable efficient lasing in the visible spectrum. Here, we report on the rapid and parallel fabrication of DFB lasers via transferring a nanograting structure from a flexible mold onto an unstructured film of the organic gain material. This geometrically well-defined structure allows for a systematic investigation of the laser threshold behavior. The laser thresholds for these devices show a strong dependence on the pump spot diameter. This experimental finding is in good qualitative agreement with calculations based on coupled-wave theory. With further investigations on various DFB laser geometries prepared by different routes and based on different organic gain materials, we found that these findings are quite general. This is important for the comparison of threshold values of various devices characterized under different excitation areas.

© 2013 Optical Society of America

1. Introduction

Since the first demonstration of lasing with organic semiconductors as gain material more than 15 years ago this material class has attracted a lot of attention [1

1. N. Tessler, G. J. Denton, and R. H. Friend, “Lasing from conjugated-polymer microcavities,” Nature 382(6593), 695–697 (1996). [CrossRef]

, 2

2. I. D. W. Samuel and G. A. Turnbull, “Organic semiconductor lasers,” Chem. Rev. 107(4), 1272–1295 (2007). [CrossRef] [PubMed]

]. Laser devices with emission within the whole visible spectrum can be realized. Further advantages are efficient energy conversion which allows optical pumping with laser diodes [3

3. T. Riedl, T. Rabe, H. H. Johannes, W. Kowalsky, J. Wang, T. Weimann, P. Hinze, B. S. Nehls, T. Farrell, and U. Scherf, “Tunable organic thin-film laser pumped by an inorganic violet diode laser,” Appl. Phys. Lett. 88(24), 241116 (2006). [CrossRef]

7

7. S. Klinkhammer, X. Liu, K. Huska, Y. Shen, S. Vanderheiden, S. Valouch, C. Vannahme, S. Bräse, T. Mappes, and U. Lemmer, “Continuously tunable solution-processed organic semiconductor DFB lasers pumped by laser diode,” Opt. Express 20(6), 6357–6364 (2012). [CrossRef] [PubMed]

] or light emitting diodes [8

8. Y. Yang, G. A. Turnbull, and I. D. W. Samuel, “Hybrid optoelectronics: A polymer laser pumped by a nitride light-emitting diode,” Appl. Phys. Lett. 92(16), 163306 (2008). [CrossRef]

, 9

9. Y. Wang, G. Tsiminis, A. L. Kanibolotsky, P. J. Skabara, I. D. W. Samuel, and G. A. Turnbull, “Nanoimprinted polymer lasers with threshold below 100 W/cm2 using mixed-order distributed feedback resonators,” Opt. Express 21(12), 14362–14367 (2013). [CrossRef] [PubMed]

] and simplicity of fabrication. Low threshold laser devices with single longitudinal mode emission can be realized using distributed feedback (DFB) structures. Thin ðlms of the active material are either obtained by processing solutions of conjugated polymers [10

10. F. Hide, M. A. Diaz-Garcia, B. J. Schwartz, M. R. Andersson, Q Pei, and A. J. Heeger, “Semiconducting polymers: A new class of solid-state laser materials,” Science 273(5283), 1833–1836 (1996). [CrossRef]

, 11

11. M. D. McGehee, M. A. Díaz-García, F. Hide, R. Gupta, E. K. Miller, D. Moses, and A. J. Heeger, “Semiconducting polymer distributed feedback lasers,” Appl. Phys. Lett. 72(13), 1536–1538 (1998). [CrossRef]

] or evaporating small molecules [12

12. V. Kozlov, V. Bulovic, P. Burrows, and S. Forrest, “Laser action in organic semiconductor waveguide and double-heterostructure devices,” Nature 389(6649), 362–364 (1997). [CrossRef]

, 13

13. D. Schneider, T. Rabe, T. Riedl, T. Dobbertin, M. Kröger, E. Becker, H.-H. Johannes, W. Kowalsky, T. Weimann, J. Wang, and P. Hinze, “Laser threshold reduction in an all-spiro guest-host system,” Appl. Phys. Lett. 85(10), 1659–1661 (2004). [CrossRef]

] on top of the grating substrates. In this manuscript, we demonstrate nanograting transfer as a novel fabrication method to fabricate organic semiconductor DFB lasers based on the small molecule tris(8-hydroxyquinoline) aluminum (Alq3) and the laser dye 4-dicyanmethylene-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM). Different from above mentioned fabrication methods, nanograting transfer is used to transfer the gratings onto a homogeneous gain material layer. It may allow for the sensing devices as spatially defined excitation sources (“laser pixels”) [14

14. X. Liu, S. Klinkhammer, K. Sudau, N. Mechau, C. Vannahme, J. Kaschke, T. Mappes, M. Wegener, and U. Lemmer, “Ink-jet-printed organic semiconductor distributed feedback laser,” Appl. Phys. Express 5(7), 072101 (2012). [CrossRef]

], which can be integrated into a photonic lab-on-a-chip (LOC) or into other sensing systems [15

15. C. Vannahme, S. Klinkhammer, M. B. Christiansen, A. Kolew, A. Kristensen, U. Lemmer, and T. Mappes, “All-polymer organic semiconductor laser chips: Parallel fabrication and encapsulation,” Opt. Express 18(24), 24881–24887 (2010). [CrossRef] [PubMed]

17

17. C. Vannahme, S. Klinkhammer, U. Lemmer, and T. Mappes, “Plastic lab-on-a-chip for fluorescence excitation with integrated organic semiconductor lasers,” Opt. Express 19(9), 8179–8186 (2011). [CrossRef] [PubMed]

]. This approach may even be combined to a roll-to-roll process and allow for a high throughput laser fabrication at low production costs.

Usually, the efficiency of such a device is determined by experimentally investigating the lasing threshold. For better comparison, the pump pulse energy is often normalized to the excitation area (fluence), sometimes also to the duration of excitation. In principle, this allows the comparison of devices which are characterized under different conditions. Recently it was shown that the excitation area for reasons of comparability is only valid if the pump spot area of optical excitation is sufficiently large [18

18. E. M. Calzado, J. M. Villalvilla, P. G. Boj, J. A. Quintana, V. Navarro-Fuster, A. Retolaza, S. Merino, and M. A. Díaz-García, “Influence of the excitation area on the thresholds of organic second-order distributed feedback lasers,” Appl. Phys. Lett. 101(22), 223303 (2012). [CrossRef]

]. The DFB laser fabricated via nanograting transfer supplies a simple geometry on the unstructured active layer. We used this device to investigate experimentally and theoretically the dependence of lasing threshold on the excitation area. Our experiments were compared with the results obtained via coupled-wave theory. A qualitative agreement was found. By further investigations on various DFB laser configurations fabricated through thermal evaporation, spin coating and horizontal dipping, we found the laser threshold fluences for all the devices decreased for increasing pump spot diameters and decreased insignificantly above a certain value between 3.0 × 10−4 cm2 and 1.0 × 10−3 cm2, depending on the type of materials and the DFB laser configurations. This is important for the comparison of threshold values of various devices characterized under different excitation areas.

2. Device design and fabrication processes

The nanograting transfer fabrication process of an organic DFB laser is depicted in Figs. 1(a)
Fig. 1 (a) Schematic illustration of the nanograting transfer. The deposited grating mold is pressed onto the unstructured organic semiconductor gain layer and then (b) detached from the device, completing the transfer of nanostructured Alq3 and NPB. (c) SEM image of the top surface of the transferred gratings and (d) of the cross section of the device.
and 1(b). A nickel (Ni) stamp with a grating area of 5 mm × 20 mm and a grating period of 400 nm was fabricated via electron beam lithography and subsequent electroplating. The Ni stamp was replicated into a TOPAS® 8007 cyclic oleðn copolymer (COC) sheet by hot embossing at a temperature of 130°C and a pressure of 2.6 MPa for 10 minutes [19

19. C. Vannahme, S. Klinkhammer, A. Kolew, P.-J. Jakobs, M. Guttmann, S. Dehm, U. Lemmer, and T. Mappes, “Integration of organic semiconductor lasers and single-mode passive waveguides into a PMMA substrate,” Microelectron. Eng. 87(5–8), 693–695 (2010). [CrossRef]

]. We obtained a COC mold with a grating period of 398 nm. To lower the surface energy of the mold, a 1 wt% Teflon (AF1601, DuPont) solution was spin-coated onto the COC mold at 3000 rpm for 60 s and then baked at 55°C for 20 min. Subsequently, layers of 35 nm of Alq3 and 15 nm of 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB) were deposited onto the Teflon-coated COC mold by thermal evaporation. For the actual laser device part, a layer of 200 nm Alq3:DCM was deposited onto an unstructured soda-lime glass substrate of edge length 25 mm and 1 mm thickness via thermal coevaporation. The Alq3/NPB deposited mold was then pressed onto the unstructured Alq3:DCM layer under a pressure of 5 MPa at 55°C for 10 min. The thin NPB layer was chosen to enhance the adhesion of Alq3 grating structures onto the Alq3:DCM active layer. Since the work of adhesion between Alq3:DCM and NPB is larger than between Alq3 and Teflon, the Alq3/NPB could be easily detached from the mold and transferred to the unstructured sample [20

20. Z. Wang, J. Hauss, C. Vannahme, U. Bog, S. Klinkhammer, D. Zhao, M. Gerken, T. Mappes, and U. Lemmer, “Nanograting transfer for light extraction in organic light-emitting devices,” Appl. Phys. Lett. 98(14), 143105 (2011). [CrossRef]

]. A scanning electron microscope (SEM) image of the grating on the final device is shown in Fig. 1(c). Figure 1(d) shows an SEM image of the cross section of the device prepared by a focused ion beam. The nanograting exhibits a height of approximately 50 nm at maximum.

The achieved nanograting transfer provides a promising way to fabricate spatially well-defined organic DFB laser devices. It utilizes economic COC grating mold to transfer modulation gratings onto the homogeneous active lasing material layer. Through controlling the location and area of the transfer range, it allows building localized functional laser pixels on a miniaturized lab-on-a-chip system without negative effects on neighboring photonic components. Compared to the conventional organic DFB lasers based on silica or glass gratings, the grating parameters and thickness of the active medium can be easily individually defined and characterized. Furthermore, such configuration may benefit for a higher confinement of laser modes in the active material layer. Hence, the laser behavior will not be strongly perturbed by grating defects or additional modulations [21

21. T. Zhai, X. Zhang, and Z. Pang, “Polymer laser based on active waveguide grating structures,” Opt. Express 19(7), 6487–6492 (2011). [CrossRef] [PubMed]

]. Due to the flexibility of the COC sheets, this approach may even be transferred to a roll-to-roll process, which allow for a high throughput laser fabrication at low production costs.

3. Optical characterization

For optical characterization, the fabricated organic DFB lasers were optically excited by a diode-pumped, actively Q-switched frequency tripled neodymium:yttrium-orthovanadate (Nd:YVO4) laser (Advanced Optical Technology Ltd., AOT-YVO-20QSP) with a wavelength of 355 nm. The pump pulses had a duration of approximately 1 ns at a repetition rate of 1.4 kHz. The pump pulse energy was adjusted with a variable neutral density ðlter and measured with a calibrated gallium arsenide phosphide photodiode connected to an oscilloscope (Tektronix, TDS2024). The sample was kept in a vacuum chamber (< 5 × 10−5 mbar) to protect the active material from photooxidation. A focusing lens was used to adjust the excitation area of the pump spot by moving the vacuum chamber with the sample relative to the focal plane. Emission from the sample was collected using the focusing lens for the pump beam, then directed through a dichroic mirror and coupled into a multimode optical ðber. Further on, the laser spectra were analyzed by a spectrograph (Acton Research Corporation, SpectraPro 300i, variable grating) connected to an intensiðed charge-coupled device camera (Princeton Research, PiMax 512). The vacuum chamber containing the sample could be moved in all three dimensions relative to the pump beam using a motorized precision stage. This allowed for a spectrally and spatially resolved characterization of the lasers. The position-dependent dimensions of the laser spot on the sample were determined using the moving edge method and fitted with a Gaussian beam profile along the horizontal (x) and vertical (y) axis [22

22. W. Plass, R. Maestle, K. Wittig, A. Voss, and A. Giesen, “High-resolution knife-edge laser beam profiling,” Opt. Commun. 134(1–6), 21–24 (1997). [CrossRef]

]. The beam emitted from the pump laser showed a slight elliptical shape. The diameters of the pump spot were taken as the extension of the pump spot along x and y for which the intensity was above 1/e2 of the intensity maximum.

The sample showed lasing operation above threshold with a lasing wavelength between 622 nm and 624 nm over the whole area of the transferred grating. This deviation can be attributed to the slightly inhomogeneous film thicknesses caused by the thermal evaporation process. Laser thresholds of the device were measured at several positions on the sample, each with different pump spot dimensions by changing the position of the sample relative to the focal plane of the pump beam. We performed the same measurements with the grating lines parallel and perpendicular to the long axis of the elliptical pump spot in order to take account of the ellipticity, as illustrated in the inset of Fig. 2(a)
Fig. 2 (a) Pump energy at threshold for varying pump spot diameters with the long axis of the elliptical pump spot perpendicular (D1) and parallel (D2) to the grating lines. (b) Fluence at threshold for varying pump spot area. Inset: Input-output characteristic of the DFB laser at wavelength of 622.5 nm measured at a pump spot area of 3.6·10−3 cm2.
. The averaged pulse energy at threshold for different pump spot diameters is shown in Fig. 2(a). Clearly, the threshold pump energy per pulse increases with growing spot dimensions. Figure 2(b) shows the same data with the threshold pulse energies normalized to the area of the elliptical pump spot. The threshold pulse energy density (fluence) is on the order of 103 µJ cm−2 for small pump spot diameters and then decreases for increasing spot diameters until it becomes almost invariant at about 10 µJ cm−2 for pump spot areas larger than 7.3 × 10−4 cm2. Depending on the spot orientation this corresponds to a spot diameter of D1 = 261 µm or D2 = 356 µm.

4. Discussions

For a given device with a corrugation only on one side of the active material, like our DFB laser fabricated through nanograting transfer, the decrease in threshold fluence with increased pump spot size can be explained via coupled-wave theory [23

23. W. Streifer, R. D. Burnham, and D. R. Scifres, “Effect of external reflectors on longitudinal modes of distributed feedback lasers,” IEEE J. Quantum Electron. 11(4), 154–161 (1975). [CrossRef]

26

26. H. Kogelnik and C. V. Shank, “Coupled-wave theory of distributed feedback lasers,” J. Appl. Phys. 43(5), 2327–2335 (1972). [CrossRef]

]. For a tooth-shaped one-dimensional grating one obtains the coupled-wave equations
R'+(g0iδ)R=iκeffS, (1.a)
S'+(g0iδ)S=iκeffR, (1.b)
where R and S are the amplitudes of the forward- and backward-propagating fields, g0 is the gain/loss, δ is the detuning from the Bragg frequency. For index coupling the first resonances are near δ ≈κ [26

26. H. Kogelnik and C. V. Shank, “Coupled-wave theory of distributed feedback lasers,” J. Appl. Phys. 43(5), 2327–2335 (1972). [CrossRef]

]. κeff is the coupling coefficient of two counter-propagating fundamental waveguide modes. In our case, due to a small modulation Δn, we can rewrite the coupling efficient as κeff ≈2Δn/λ [27

27. A. Yariv, Optical Electronics in Modern Communications (Oxford University, 1997).

]. Δn is the refractive index perturbation, in our case, Δn ≈0.012 as determined by using the eigenmode expansion simulation tool CAMFR [28].

The general solution of the coupled wave Eqs. (1.a) and (1.b) is of the form
R(z)=r1eγz+r2eγz, (2.a)
S(z)=s1eγz+s2eγz, (2.b)
with constants of r1, r2, s1, s2 and the complex propagation constant γ obeying the dispersion relation
γ2=(g0iδ)2+κeff2.
(3)
From Eqs. (1.a) and (1.b) an implicit threshold condition for a DFB laser device of length L is derived:
κeff=±iγ/sinhγL.
(4)
We consider the effective device length L to be equal to the pump spot length perpendicular to the grating lines Lp and the approximate pump spot area πLp2/4 can be written as πL2/4.

Combining Eqs. (3)(5) we can calculate the threshold fluence for different device lengths L. We note that this approach has been elaborated for the first order DFB lasers. As we are using the second order DFB lasers, the calculated threshold comprises the gain being necessary to compensate for the out-coupling via first order Bragg scattering.

As shown in Figs. 3(a)
Fig. 3 Calculated laser threshold fluence in comparison to experiments results for varying (a) pump spot area and (b) coupling strength with the long axis of the elliptical pump spot perpendicular (D1) and parallel (D2).
and 3(b), we find that the laser threshold fluence decreases with growing excitation area and coupling strength κeffL. We are able to reproduce the saturation-like behavior of the threshold fluence above a certain circular pump spot area. Similar to the prediction made by Kogelnik et al. [26

26. H. Kogelnik and C. V. Shank, “Coupled-wave theory of distributed feedback lasers,” J. Appl. Phys. 43(5), 2327–2335 (1972). [CrossRef]

], when the pump spot is too small and coupling strength κeffL < 1, the device is excited at a state of “undercoupling”. Due to the deficiency of coupling, the laser threshold is much higher compared to the sufficient coupling strength. Conversely, when the pump spot is increased to another limit, in our case κeffL ≥ 5, the device will be excited at a state of “overcoupling”. Hence, the laser threshold influence cannot be further decreased and reaches a saturation value. It can be noticed that our measured laser threshold fluences decrease faster than the theoretical prediction at small excitation areas. We attribute this to the approximation of device length L in the calculation. We considered that the effective device length L is equal to the pump area length perpendicular to the grating lines Lp and only the illuminated gratings contribute to the laser oscillation. However, the number of the grating lines contributing to the distributed feedback is actually larger than the grating number included in the excitation area (L > Lp). Due to this reason, the theoretical simulation shows a slower decrease in laser threshold fluence.

The minimum excitation area that is required in order to provide comparability of threshold fluences varies for different coupling coefficients. We find that in our measurements and simulations the threshold fluences do not vary significantly above a spot area at about 1.0 × 10−3 cm2. Hence, we conclude that a minimum pump spot area needs to be given in order to deduce comparable threshold fluences in optically excited organic semiconductor DFB lasers.

Organic semiconductor DFB lasers can be realized through different fabrication methods in a large number of variants. The different corrugation schemes will result in different coupling mechanisms. The devices have in general neither pure index coupling nor pure gain coupling. Both coupling mechanisms contribute to the laser emission and the theoretical treatment becomes increasingly complex. To further investigate the decrease of laser threshold fluence with increased pump spot size, we have fabricated various organic DFB lasers and derived a general upper value of the pump spot size to compare the laser threshold fluences of the second order DFB laser devices.

Firstly, we fabricated an organic semiconductor DFB laser with the established thermal evaporation method. A layer of 350 nm Alq3:DCM was deposited onto a silica grating substrate with grating period of 400 nm and grating height of 90 nm. The atomic force microscope (AFM) images in Figs. 4(a)
Fig. 4 (a) Exemplary atomic force image of the surface corrugation on an organic small molecule DFB laser after Alq3:DCM thermal evaporation. (b) Atomic force micrographs of two surface corrugation patterns before and after thermal evaporation. (c) Laser threshold fluences and threshold pump energy varying with pump spot area. Inset: laser spectrum with the peak at 640.6 nm.
and 4(b) show the surface corrugation after deposition, which has a good accordance with the original grating pattern. The laser thresholds of the devices were measured at different pump spot sizes and the normalized laser threshold fluences are shown in Fig. 4(c). For pump spot areas larger than 3.0 × 10−4 cm2 the laser threshold density levels off and decreases only insignificantly.

5. Conclusion

In summary, we fabricated organic semiconductor DFB lasers by transferring a nanograting structure from a flexible mold onto an unstructured film of the organic gain material, which allows building localized functional laser pixels on a miniaturized lab-on-a-chip system. The grating parameters and thickness of the active medium can be individually defined. This may, e.g., allow for a higher confinement of laser modes in the active material layer and hence a higher stability in laser performance. We used this device to investigate the dependence of the lasing threshold on the excitation area and found that the threshold fluence did not vary significantly for excitation areas above a certain value. Using coupled-wave theory, we performed calculations to investigate the threshold behavior as a function of the excitation area and found a qualitative agreement with our experimental data. By further investigations on various DFB laser modulation configurations made from different organic gain materials, we found that this pump spot size dependence is generally valid. This is important in the field of DFB lasers as it allows the comparison of threshold values of different devices measured in different setups.

Acknowledgments

The authors thank A. Egel for advices on the theoretical calculations. This work was supported by the Deutsche Forschungsgemeinschaft and the State of Baden-Württemberg through the subproject A 4.10 of the DFG-Center for Functional Nanostructures (CFN). X.L. acknowledges support from the Carl Zeiss Stiftung and Z.W. acknowledges support from the Alexander von Humboldt foundation. The work of S.K., T.W., X.L., and C.V. is supported by the Karlsruhe School of Optics & Photonics (KSOP). T.M.’s Young Investigator Group received financial support from the “Concept for the Future” of Karlsruhe Institute of Technology within the framework of the German Excellence Initiative. We acknowledge support by Deutsche Forschungsgemeinschaft and Open Access Publishing Fund of Karlsruhe Institute of Technology. This work was partly carried out with the support of the Karlsruhe Nano Micro Facility (KNMF), a Helmholtz Research Infrastructure at Karlsruhe Institute of Technology.

References and links

1.

N. Tessler, G. J. Denton, and R. H. Friend, “Lasing from conjugated-polymer microcavities,” Nature 382(6593), 695–697 (1996). [CrossRef]

2.

I. D. W. Samuel and G. A. Turnbull, “Organic semiconductor lasers,” Chem. Rev. 107(4), 1272–1295 (2007). [CrossRef] [PubMed]

3.

T. Riedl, T. Rabe, H. H. Johannes, W. Kowalsky, J. Wang, T. Weimann, P. Hinze, B. S. Nehls, T. Farrell, and U. Scherf, “Tunable organic thin-film laser pumped by an inorganic violet diode laser,” Appl. Phys. Lett. 88(24), 241116 (2006). [CrossRef]

4.

A. E. Vasdekis, G. Tsiminis, J.-C. Ribierre, L. O’ Faolain, T. F. Krauss, G. A. Turnbull, and I. D. W. Samuel, “Diode pumped distributed bragg reflector lasers based on a dye-to-polymer energy transfer blend,” Opt. Express 14(20), 9211–9216 (2006). [CrossRef] [PubMed]

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C. Karnutsch, M. Stroisch, M. Punke, U. Lemmer, J. Wang, and T. Weimann, “Laser diode-pumped organic semiconductor lasers utilizing two-dimensional photonic crystal resonators,” IEEE Photon. Technol. Lett. 19(10), 741–743 (2007). [CrossRef]

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H. Sakata, K. Yamashita, H. Takeuchi, and M. Tomiki, “Diode-pumped distributed-feedback dye laser with an organic–inorganic microcavity,” Appl. Phys. B 92(2), 243–246 (2008). [CrossRef]

7.

S. Klinkhammer, X. Liu, K. Huska, Y. Shen, S. Vanderheiden, S. Valouch, C. Vannahme, S. Bräse, T. Mappes, and U. Lemmer, “Continuously tunable solution-processed organic semiconductor DFB lasers pumped by laser diode,” Opt. Express 20(6), 6357–6364 (2012). [CrossRef] [PubMed]

8.

Y. Yang, G. A. Turnbull, and I. D. W. Samuel, “Hybrid optoelectronics: A polymer laser pumped by a nitride light-emitting diode,” Appl. Phys. Lett. 92(16), 163306 (2008). [CrossRef]

9.

Y. Wang, G. Tsiminis, A. L. Kanibolotsky, P. J. Skabara, I. D. W. Samuel, and G. A. Turnbull, “Nanoimprinted polymer lasers with threshold below 100 W/cm2 using mixed-order distributed feedback resonators,” Opt. Express 21(12), 14362–14367 (2013). [CrossRef] [PubMed]

10.

F. Hide, M. A. Diaz-Garcia, B. J. Schwartz, M. R. Andersson, Q Pei, and A. J. Heeger, “Semiconducting polymers: A new class of solid-state laser materials,” Science 273(5283), 1833–1836 (1996). [CrossRef]

11.

M. D. McGehee, M. A. Díaz-García, F. Hide, R. Gupta, E. K. Miller, D. Moses, and A. J. Heeger, “Semiconducting polymer distributed feedback lasers,” Appl. Phys. Lett. 72(13), 1536–1538 (1998). [CrossRef]

12.

V. Kozlov, V. Bulovic, P. Burrows, and S. Forrest, “Laser action in organic semiconductor waveguide and double-heterostructure devices,” Nature 389(6649), 362–364 (1997). [CrossRef]

13.

D. Schneider, T. Rabe, T. Riedl, T. Dobbertin, M. Kröger, E. Becker, H.-H. Johannes, W. Kowalsky, T. Weimann, J. Wang, and P. Hinze, “Laser threshold reduction in an all-spiro guest-host system,” Appl. Phys. Lett. 85(10), 1659–1661 (2004). [CrossRef]

14.

X. Liu, S. Klinkhammer, K. Sudau, N. Mechau, C. Vannahme, J. Kaschke, T. Mappes, M. Wegener, and U. Lemmer, “Ink-jet-printed organic semiconductor distributed feedback laser,” Appl. Phys. Express 5(7), 072101 (2012). [CrossRef]

15.

C. Vannahme, S. Klinkhammer, M. B. Christiansen, A. Kolew, A. Kristensen, U. Lemmer, and T. Mappes, “All-polymer organic semiconductor laser chips: Parallel fabrication and encapsulation,” Opt. Express 18(24), 24881–24887 (2010). [CrossRef] [PubMed]

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C. Vannahme, S. Klinkhammer, U. Lemmer, and T. Mappes, “Plastic lab-on-a-chip for fluorescence excitation with integrated organic semiconductor lasers,” Opt. Express 19(9), 8179–8186 (2011). [CrossRef] [PubMed]

18.

E. M. Calzado, J. M. Villalvilla, P. G. Boj, J. A. Quintana, V. Navarro-Fuster, A. Retolaza, S. Merino, and M. A. Díaz-García, “Influence of the excitation area on the thresholds of organic second-order distributed feedback lasers,” Appl. Phys. Lett. 101(22), 223303 (2012). [CrossRef]

19.

C. Vannahme, S. Klinkhammer, A. Kolew, P.-J. Jakobs, M. Guttmann, S. Dehm, U. Lemmer, and T. Mappes, “Integration of organic semiconductor lasers and single-mode passive waveguides into a PMMA substrate,” Microelectron. Eng. 87(5–8), 693–695 (2010). [CrossRef]

20.

Z. Wang, J. Hauss, C. Vannahme, U. Bog, S. Klinkhammer, D. Zhao, M. Gerken, T. Mappes, and U. Lemmer, “Nanograting transfer for light extraction in organic light-emitting devices,” Appl. Phys. Lett. 98(14), 143105 (2011). [CrossRef]

21.

T. Zhai, X. Zhang, and Z. Pang, “Polymer laser based on active waveguide grating structures,” Opt. Express 19(7), 6487–6492 (2011). [CrossRef] [PubMed]

22.

W. Plass, R. Maestle, K. Wittig, A. Voss, and A. Giesen, “High-resolution knife-edge laser beam profiling,” Opt. Commun. 134(1–6), 21–24 (1997). [CrossRef]

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W. Streifer, R. D. Burnham, and D. R. Scifres, “Effect of external reflectors on longitudinal modes of distributed feedback lasers,” IEEE J. Quantum Electron. 11(4), 154–161 (1975). [CrossRef]

24.

W. Streifer, D. R. Scifres, and R. D. Burnham, “Analysis of grating-coupled radiation in GaAs:GaAlAs lasers and waveguides,” IEEE J. Quantum Electron. 12(7), 422–428 (1976). [CrossRef]

25.

W. Streifer, D. R. Scifres, and R. D. Burnham, “Coupled wave analysis of DFB and DBR lasers,” IEEE J. Quantum Electron. 13(4), 134–141 (1977). [CrossRef]

26.

H. Kogelnik and C. V. Shank, “Coupled-wave theory of distributed feedback lasers,” J. Appl. Phys. 43(5), 2327–2335 (1972). [CrossRef]

27.

A. Yariv, Optical Electronics in Modern Communications (Oxford University, 1997).

28.

CAMFR, http://camfr.sourceforge.net.

29.

S. Riechel, “Organic semiconductor lasers with two-dimensional distributed feedback,” PhD thesis (Ludwig-Maximilians-Universität München, 2002).

30.

S. Riechel, U. Lemmer, J. Feldmann, S. Berleb, A. G. Mückl, W. Brütting, A. Gombert, and V. Wittwer, “Very compact tunable solid-state laser utilizing a thin-film organic semiconductor,” Opt. Lett. 26(9), 593–595 (2001). [CrossRef] [PubMed]

31.

V. Navarro-Fuster, I. Vragovic, E. M. Calzado, P. G. Boj, J. A. Quintana, J. M. Villalvilla, A. Retolaza, A. Juarros, D. Otaduy, S. Merino, and M. A. Díaz-García, “Film thickness and grating depth variation in organic second-order distributed feedback lasers,” J. Appl. Phys. 112(4), 043104 (2012). [CrossRef]

OCIS Codes
(140.3430) Lasers and laser optics : Laser theory
(140.3490) Lasers and laser optics : Lasers, distributed-feedback
(140.7300) Lasers and laser optics : Visible lasers

ToC Category:
Lasers and Laser Optics

History
Original Manuscript: October 14, 2013
Manuscript Accepted: October 21, 2013
Published: November 4, 2013

Citation
Xin Liu, Sönke Klinkhammer, Ziyao Wang, Tobias Wienhold, Christoph Vannahme, Peter-Jürgen Jakobs, Andreas Bacher, Alban Muslija, Timo Mappes, and Uli Lemmer, "Pump spot size dependent lasing threshold in organic semiconductor DFB lasers fabricated via nanograting transfer," Opt. Express 21, 27697-27706 (2013)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-23-27697


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