Open Access
Add to BibSonomy
Abstract
A hybrid membrane is employed as a high-order plasmonic distributed feedback (DFB) cavity to reduce the lasing threshold of polymer lasers. The hybrid membrane consists of an anodic aluminum oxide (AAO) membrane, a 25 nm thick silver layer and a free-standing polymer membrane. The AAO membrane is fabricated by a low-cost, single chemical etching method. Then, a layer of silver with a thickness of 25 nm is sputtered on the surface of the AAO. Subsequently, a polymer membrane is directly attached to the silver-plated AAO membrane, forming an AAO/silver/polymer hybrid membrane. Under optical pumping conditions, low-threshold, three-order DFB lasing is observed. The proposed laser device exhibited a dual-threshold characteristic because of the evolution from amplified spontaneous emission to DFB lasing. And a significant shift from omnidirectional emission to directional emission lasing can be observed while the pump energy density is beyond the second threshold. Furthermore, the plasmonic enhancement sourced from silver corrugation reveals important improvement effects to the DFB lasing of AAO/silver/polymer hybrid membrane for decreasing threshold, narrowing full width at half maximum (FWHM), and an increasing Q factor. This work may promote the design and production of low-cost and large-area high-order plasmonic DFB polymer lasers.
© 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. Introduction
Compared with conventional lasers, DFB polymer lasers are regarded as one of the most promising thin-film polymer lasers for potential applications due to their broad emission spectra, low threshold, and simple fabrication method [1–5]. Two kinds of DFB cavity configurations are usually employed. In the first kind, Bragg grating structures are written into polymers so that the polymer material acts as both a DFB cavity and gain medium [6–9]. For the second configuration, polymers are attached onto the surfaces of the DFB cavities [10–13]. To prepare the above DFB cavities, many methods, such as electron beam lithography [14,15], self-organization [16], nanoimprinting [17–20], direct writing [21–23], and interference lithography [24–26], can be used. However, until now, virtually all of the manufacturing methods of DFB cavities have been physical methods, all of which are expensive and require sophisticated equipment. There are few reports about the successful fabrication of a DFB cavity by a single chemical method to emit DFB lasing.
In this work, an AAO membrane made by a single electrochemical etching method is employed as a DFB cavity, which is accompanied by a silver-plated layer and polymer membrane to form an AAO/silver/polymer hybrid membrane, which can be stimulated to emit high-order plasmonic DFB polymer lasing. The AAO membrane is the main cavity structure of the hybrid membrane. A silver-plated layer is used to provide plasmonic enhancement to reduce the DFB lasing threshold, narrow the full width at half maximum (FWHM), and increase the Q factor. The free-standing polymer membrane is applied to produce gain feedback. Depending on experimental measurements, the emission intensity and FWHM of AAO/silver/polymer hybrid membrane lasing as a function of the pump energy density are systematically researched, and the spatial emission performance is also explored. The results show that the light emission from the AAO/silver/polymer hybrid membrane exhibits dual-threshold characteristics because of the evolution from amplified spontaneous emission (ASE) to DFB lasing and displays directional emission properties due to Bragg diffraction.
2. Experiments and methods
2.1. Preparation of AAO/silver/polymer hybrid membrane
A water-soluble polyvinyl alcohol (PVA 107, Celanese Chemicals, Germany) solution with a concentration of 40 mg/ml was spin-coated on a glass substrate with a rotational speed of 1500 r/min last 30 s, forming an approximately 350 nm thick membrane. Then, PFO [9,9-dioctylfluorenyl-2,7-diyl] (Mw= 140,000, American Dye Source Inc., Baie DDUrfe, QC, Canada) was dissolved in xylene to form a PFO solution with a concentration of 12.5 mg/ml. A PFO membrane with a thickness of approximately 150 nm was fabricated by spin-coating PFO solution above the PVA membrane with a rotational speed of 3000 r/min last 30 s. The bilayer structure was then immersed into deionized water to dissolve the PVA membrane. The remaining PFO membrane was detached from the glass substrate, forming a light-emitting and transplantable PFO membrane (15 mm × 15 mm), which can act as an active polymer layer for the laser. The wet PFO membrane was directly attached onto the silver-plated AAO membrane, which was made by sputtering silver onto the AAO (the AAO is fabricated by the well-known method of Ref. [27], and the detailed parameters and processes are as supplemental document shown). The PFO membrane can stick tightly on the surface of the silver-plated AAO membrane after drying naturally at room temperature due to the surface tension, thereby forming the AAO/silver/polymer hybrid membrane, which was researched in this work.
2.2. Optical measurements
As Fig. 1 shown, during the optical measurements, a short-pulsed, diode-pumped solid-state laser (343 nm, 1 ns, 300 Hz, Coherent Inc., Santa Clara, CA, USA) was employed as the pump source. The pump beam irradiated from the bottom side of the AAO/silver/polymer hybrid membrane with an incident spot of approximately 1 mm in diameter, and the pump power can be adjusted by a neutral optical attenuator. The emission spectra were recorded from the transmission side of the hybrid membrane by an optical fiber spectrometer (Maya 2000 Pro, Ocean Optics, USA) with spectral resolution of 0.1 nm. The distance between the hybrid membrane and the spectrometer probe remained at approximately 10 cm. An angle parameter θ was introduced to characterize the detection direction with respect to the normal direction of the hybrid membrane surface.
Fig. 1. The schematic of the optical layout for the lasing intensity and emission direction measurement experiments.
2.3. Simulations
The electrical field distribution around Ag that was plated on the AAO surface was simulated by the commercial software FDTD Solutions based on the finite difference time domain (FDTD) method. In the simulations, a simplified model of Ag that was plated on an AAO surface was built according to the experimental sample parameters from SEM characterizations. The permittivity of Ag and AAO (Al2O3) was taken from the database of the FDTD Solutions software. The refraction index of the medium around the model was 1. The excitation wavelength was 343 nm, which corresponded to the experimental pump wavelength. To produce accurate simulation results, the grid of the mesh was set to 0.5 nm.
3. Results and discussions
The porous structure of the single-channel AAO membrane, which was fabricated by the two-step anodization method, is displayed by the SEM images in Figs. 2 (a)-(c). Figure 2 (a) shows the morphology of the AAO membrane surface with a 25 nm silver-plated layer, illustrating an ordered array of hexagonally-packed circular pores, whose diameters can be tuned from 10 nm to 500 nm by changing the anodization voltage and electrolyte [28]. Figure 2 (b) shows a cross-sectional image of the AAO membrane, demonstrating that the interior of the AAO membrane is full of nanochannels, which are smooth, straight, parallel to each other, and perpendicular to the surface of the AAO membrane. Figure 2 (c) is the SEM image of the AAO membrane’s bottom, and every hexagonal unit is a closed bottom of a nanochannel. Therefore, the bottom of the single-channel AAO membrane is also referred to as the barrier layer. For the formation of AAO membrane, plenty of models have been put forward to describe and explain, such as volume expansion stress model [29], field-assisted dissolution model [30], and so on. However, there is currently no single model that can systematically describe and explain all of the phenomena in the process of AAO formation [28]. Thus, new models are still needed to supplement and improve the theoretical system framework of the entire AAO formation.
Fig. 2. (a) The SEM image of the AAO membrane surface with a 25 nm silver-plated layer. (b) The AAO cross-sectional SEM image. (c) The AAO bottom SEM image. (d) The statistical distributions of the AAO pore diameter and pore center distance. The green histogram is the statistical distribution of the pore diameter, and the corresponding red curve is its fitting curve. The yellow histogram is the statistical distribution of the pore center distance, and the corresponding blue curve is its fitting curve. (e) The statistical distribution of the triangular Ag nanodot side length and gap distance between its two neighboring Ag nanodots on the AAO surface. The orange histogram is the statistical distribution of the triangular Ag nanodot side length, and the corresponding cyan curve is its fitting curve. The olive histogram is the statistical distribution of the gap distance between the two neighboring Ag nanodots, and the corresponding violet curve is its fitting curve.
The structural characteristics of the AAO membrane include the pore diameter (Dp), pore center distance (Dc), pore density (ρ) and porosity (σ). The statistical distributions of the AAO’s Dp and Dc in this work are shown in Fig. 2 (d). The green histogram is the statistical distribution of the Dp, and the corresponding red curve is its fitting curve, which indicates that the Dp of the AAO is approximately 59.6 nm. The yellow histogram is the statistical distribution of Dc, and the corresponding blue curve is its fitting curve, which reveals that the Dc of the AAO is approximately 113.1 nm. In theory, the Dp and Dc are linearly proportional to the anodizing voltage U, and they comply with Eqs. (1) and (2) [31,32]:
where the proportionality constant λp is 1.29 nm/V and λc is 2.5 nm/V. Hence, in this research, the theoretical value of the Dp is 58.05 nm at U = 45 V, which is very similar to the experimental statistically-fitted value of 59.6 nm from Fig. 2 (d). The theoretical value of the Dc is 112.5 nm at U = 45 V, which is also similar to the experimental statistically-fitted value of 113.1 nm from Fig. 2 (d). According to the experimental statistic data of the Dp and Dc, and the well-known Eqs. (3) and (4) [33]:In Fig. 2 (a), there are obvious ridges in six vertices of each hexagonal lattice, and all the ridges are triangular Ag nanodots formed by Ag that was plated on the ridge of the AAO membrane surface. The statistical distribution data of the triangular Ag nanodot’s side length and gap distance between its two neighboring Ag nanodots are shown in Fig. 2 (e). The orange histogram is the statistical distribution of the side length from the triangular Ag nanodot, and the corresponding cyan curve is its fitting curve, which indicates that the side length of the triangular Ag nanodot is approximately 43.2 nm. The olive histogram is the statistical distribution of the gap distance between the two neighboring Ag nanodots, and the corresponding violet curve is its fitting curve, which reveals that the gap distance is approximately 29.2 nm. These statistical parameters will be used for model building of FDTD simulations in a later section.
Figure 3 (a)-(h) shows the fabrication process schematics of AAO/silver/polymer hybrid membrane. Figure 3 (a) is the glass substrate for PFO membrane preparation. After spin-coating water solution of PVA, a layer of water-soluble PVA membrane is formed on the glass substrate, as Fig. 3 (b) shown. Then, Xylene solution of PFO is spin-coated on PVA membrane, forming a thin layer of water-insoluble PFO membrane, as Fig. 3 (c) shown. The double layer membrane glass substrate is immersed into water to dissolve PVA membrane, as Fig. 3 (d) shown. Because of the dissolution of PVA membrane, a layer of free-standing PFO membrane is stripped from glass substrate, and can work as a lasing active polymer layer, as Fig. 3 (e) shown. Figure 3 (f) is the structure schematic of AAO. After plating silver by ion sputtering, a piece of silver-plated AAO membrane is obtained, as Fig. 3 (g) shown. At last, the free-standing PFO membrane is attached on the surface of silver-plated AAO, and thereby forming an AAO/silver/polymer hybrid membrane, which is researched in this work, as Fig. 3 (h) shown. Figure 3 (i) surrounded by green dotted line is the cross-section schematic of AAO/silver/polymer hybrid membrane.
Fig. 3. The schematic of (a) glass substrate, (b) PVA membrane on glass, (c) PFO membrane on PVA covered glass, (d) water dissolving to remove PVA membrane, (e) free-standing PFO membrane, (f) AAO, (g) silver-plated AAO, (h) AAO/silver/polymer hybrid membrane, (i) the cross-section of AAO/silver/polymer hybrid membrane.
Figure 4 (a) shows the evolution of the emission intensity and FWHM as a function of the pump energy density in the AAO/silver/polymer hybrid membrane lasing experiment. There are two clear threshold behaviors with two curved points in the green emission intensity curve of Fig. 4 (a) as the pump energy density increases. The first threshold is at 42.44 µJ/cm2, and the second threshold is at 193.53 µJ/cm2. The FWHM of more than 13 nm rapidly decreases when the pump energy density is stronger than the first threshold. Figure 4 (b) displays the emission spectra under the pump energy densities of 7.21 µJ/cm2, 42.44 µJ/cm2, 193.53 µJ/cm2 and 197.77 µJ/cm2, which are shown as the orange, blue, olive and red curves, respectively. The insertion of Fig. 4 (b) is used to depict the enlarged view of the emission peak under a pump energy density of 197.77 µJ/cm2, which shows that the emission peak is centered at 451.5 nm with a FWHM of approximately 2.26 nm. Therefore, the Q factor of AAO/silver/polymer lasing can be calculated to be 200.
Fig. 4. (a) The evolution of the emission intensity (green curve) and FWHM (red curve) as a function of the pump energy density in the AAO/silver/polymer lasing experiment. The green shadow area is the pump energy density range of ASE, and the yellow shadow area is the pump energy density range of DFB lasing. (b) The emission spectra under the pump energy densities of 7.21 µJ/cm2, 42.44 µJ/cm2, 193.53 µJ/cm2 and 197.77 µJ/cm2. The insert is the enlarged view of the emission peak under a pump energy density of197.77 µJ/cm2. (c) The normalized experimental emission intensity as a function of detection angle θ under a pump energy density of 106.95 µJ/cm2, which is stronger than the first threshold but weaker than the second threshold. (d) The normalized experimental emission intensity curve as a function of the detection angle θ under a pump energy density of 197.77 µJ/cm2, which is stronger than the second threshold. (e) The experimental DFB lasing spot emitted from the AAO/silver/polymer hybrid membrane.
Furthermore, the spatial emission performance of AAO/silver/polymer hybrid membrane lasing is researched by changing the detection angle θ from 80° to -80°. During the angle-resolved measurements, the distance between the spectrometer probe and sample remained at approximately 10 cm. The schematic of the optical layout for the direction measurement experiments is shown in Fig. 1. The blue curve in Fig. 4 (c) shows the normalized experimental emission intensity as a function of the detection angle θ under a pump energy density of 106.95 µJ/cm2, which is stronger than the first threshold but weaker than the second threshold. The blue curve exhibits no significant abrupt intensity variation from the 80° to -80° detection directions. The gentle intensity variation in the whole measurement range demonstrates that the light emission between the first and second thresholds is omnidirectional without directional emission characteristics. According to the omnidirectional emission performance in Fig. 4 (c) and the spectrum line-type of the first threshold in Fig. 4 (b), the emission light from the AAO/silver/polymer hybrid membrane should be ASE when the pump energy density is between the first and second thresholds, as shown by the blue shaded area in Fig. 4 (a). Therefore, the first threshold of 42.44 µJ/cm2 is the ASE threshold. Figure 4 (d) shows the normalized experimental emission intensity curve as a function of the detection angle θ under a pump energy density of 197.77 µJ/cm2, which is stronger than the second threshold. The orange normalized output intensity curve displays significant intensity fluctuations in different detection directions. In particular, the intensities rapidly increase in the range of angles of 10° ∼ 24° and -10° ∼ -24°. Two maximums appear along the approximately ±20° directions. The FWHM of the two maximum peaks in Fig. 4 (d) are both approximately 7°. The reason of this directional emission phenomenon has two possibilities, the first is random lasing under oriented scattering, the second is the emission of DFB lasing. It is well known that there is no essential difference between ASE and random lasing. If the directional emission phenomenon is derived from random lasing under oriented scattering, the same directional emission phenomenon will be also observed in the ASE emission direction experiments of Fig. 4 (c). However, the emission direction in Fig. 4 (c) is omnidirectional but not directional. Therefore, the directional emission should be DFB lasing but not random lasing under oriented scattering. In addition, another work displays that, for random lasing under oriented scattering, the intensity differences between the major directional emission direction and other emission directions are not very significant, the average base line in angular emission spectra is high [34]. However, in the angular emission spectra of Fig. 4 (d), the average base line is obviously much lower than the major directional emission peak, the intensity differences between the major directional emission direction and other emission directions are very significant. The phenomenon in Fig. 4 (d) further indicates that the directional emission should not be random lasing under oriented scattering but DFB lasing. And according to the above two conclusions, the second threshold of 193.53 µJ/cm2 is the threshold of the DFB lasing.
The experimental DFB lasing spot in the angle range from 0° to +80° is shown in Fig. 4 (e). The inner area of the red circle is the AAO/silver/polymer hybrid membrane, and an object photograph is shown in the left insert of Fig. 4 (e). The yellow arrow in Fig. 4 (e) notes the pump light spot on the AAO/silver/polymer hybrid membrane. Relying on the scatter pump light, the attached PFO membrane can be seen, as marked by the cyan arrow in Fig. 4 (e). The inner area of the green square in Fig. 4 (e) is the spot of the DFB lasing emitted from the AAO/silver/polymer hybrid membrane.
The directional emission of the DFB lasing in Fig. 4(d) can be attributed to the Bragg diffraction effect from the periodic lattice structure of the AAO membrane, which is equal to a grating. The emission direction satisfies the diffraction condition (5) [35,36]:
To research the effect of plasmonic enhancement on the DFB lasing emitted from the AAO/silver/polymer hybrid membrane, an AAO/polymer hybrid membrane without sliver is fabricated by attaching a PFO membrane onto the surface of the AAO membrane directly. Figure 5 (a) depicts the evolution of the emission spectra by varying the pump energy densities in the AAO/polymer lasing experiments. The green emission intensity curve indicates that the light emission of the AAO/polymer hybrid membrane still had dual-threshold performance with two curved points. The first threshold is at 1.25 mJ/cm2, and the second threshold is at 3.40 mJ/cm2. According to the previous experiments, it is known that the first threshold is the threshold of the ASE and the second one is the threshold of the DFB lasing. This conclusion can also be verified from Fig. 5 (b). Figure 5 (b) displays the emission spectra under the pump energy densities of 1.22 mJ/cm2, 1.25 mJ/cm2, 3.40 mJ/cm2 and 3.58 mJ/cm2, which are shown as the orange, blue, olive and red curves, respectively. The blue spectrum of the first threshold shows an obvious ASE line-type, and the olive spectrum of the second threshold displays a significant lasing line-type. The contrast of Fig. 5 (a) and Fig. 4 (a) demonstrates that the DFB lasing threshold is increased approximately 18 times in the condition without silver and plasmonic enhancement. The inclusion of Fig. 5 (b) shows the enlarged view of the emission peak under a pump energy density of 3.58 mJ/cm2, which depicts that the emission peak is centered at 450.4 nm with a FWHM of approximately 2.7 nm. Therefore, the Q factor of the AAO/polymer lasing without silver can be calculated to be 167. In contrast to the DFB lasing from the AAO/silver/polymer hybrid membrane, the peak position of the DFB lasing from the AAO/polymer hybrid membrane has a 1.1 nm blueshift, the FWHM produces a 0.44 nm widening, and the Q factor decreases by 33. Therefore, the plasmonic enhancement sourced from silver has important improvement effects on the DFB lasing of the AAO/silver/polymer hybrid membrane for reducing the threshold, narrowing the FWHM and increasing the Q factor.
Fig. 5. (a) The evolution of the emission intensity (green curve) and FWHM (red curve) as a function of the pump energy density in the AAO/polymer lasing experiment. The green shadow area is the pump energy density range of ASE, and the yellow shadow area is the pump energy density range of DFB lasing. (b) The emission spectra under the pump energy densities of 1.22 mJ/cm2, 1.25 mJ/cm2, 3.40 mJ/cm2 and 3.58 mJ/cm2. This inclusion is an enlarged view of the emission peak under a pump energy density of 3.58 m J/cm2. (c) The electric field distribution of the 343 nm pump light in AAO/silver/polymer hybrid membrane. (d) The electric field distribution of the 343 nm pump light in AAO/polymer hybrid membrane without silver.
Two computer models are built by commercial software FDTD solutions for calculating the plasmonic enhancement effect in the AAO/silver/polymer hybrid membrane from theory. The models have the same morphology and physics parameters as the experimental samples. Figure 5 (c) is the simulation result of the AAO/silver/polymer hybrid membrane, which shows the electric field distribution of the 343 nm pump light along the interface of the triangular Ag nanodots and PFO membrane. Because of plasmonic enhancement, the local electric fields of the 343 nm pump light around triangular Ag nanodots are increased to approximately 4.5 times stronger than those in air, which can intensely enhance the emission from the AAO/silver/polymer hybrid membrane [37–42]. Figure 5 (d) is the simulation result of the AAO/polymer hybrid membrane without silver, which shows the electric field distribution of the 343 nm pump light along the interface of the AAO and PFO membranes. Because there is no silver used to produce plasmonic enhancement, the local electric fields of the 343 nm pump light only have a 1.1 times enhancement contrast in air and mainly focus on the nanoholes of the AAO. According to classical Maxwell electromagnetic theory, light is an electromagnetic wave in essence, and its intensity is proportional to the square of its own electric field intensity. Thus, a 4.5-fold electric field enhancement is equivalent to that the power of the 343 nm pump light is amplified approximately 20 times in the AAO/silver/polymer hybrid membrane, and a 1.1-fold electric field enhancement is equivalent to that the power of the 343 nm pump light is amplified just 1.2 times in the AAO/polymer hybrid membrane without silver. If 20 is divide by 1.2, the result will be approximately 17, which is very similar to the experimental 18 times threshold reduction of the AAO/silver/polymer DFB lasing compared to the AAO/polymer DFB lasing.
In addition to plasmonic enhancement, another important reason also leads to the threshold reduction of the DFB lasing from the AAO/silver/polymer hybrid membrane, which is the special structure formed by attaching the PFO membrane onto the array of triangular Ag nanodots. In the structure of the AAO/silver/polymer hybrid membrane, the PFO membrane is supported by an array of triangular Ag nanodots formed by silver that was plated onto the AAO ridges, as shown in Fig. 3 (i). This kind of structure leads to a small contact area between the silver and the active polymer membrane, and many air gaps exist between every two neighboring Ag nanodots. A small metallic contact area and many air gaps can provide a strong diffraction effect to enhance the feedback strength, make the mode more photonic, and produce less ohmic losses inherent in metals [43]. Although the effect of the structure on the threshold reduction is important, it is unfortunate that no quantitative calculation method for this effect has been reported in previous researches and literature.
4. Conclusion
An AAO/silver/polymer hybrid membrane is achieved by attaching an active PFO membrane onto the surface of a silver-plated AAO membrane. This membrane depicts dual-threshold and directional emission properties. The first and second thresholds belong to the ASE and DFB lasing, respectively. For the AAO/silver/polymer hybrid membrane, the ASE threshold is 42.44 µJ/cm2, and the DFB lasing threshold is 193.53 µJ/cm2; it exhibits directional emission characteristics along the ±20° direction with a 7° divergence angle. Based on the plasmonic enhancement of silver, the threshold of the DFB lasing from the AAO/silver/polymer hybrid membrane has an 18-fold reduction compared with the AAO/polymer hybrid membrane without silver. The existence of silver between the AAO and the polymer has important improvement effects on the DFB lasing of AAO/silver/polymer hybrid membranes by decreasing the threshold, narrowing the FWHM and increasing the Q factor.
Funding
Beijing Municipal Natural Science Foundation (Z180015); National Natural Science Foundation of China (61822501).
Disclosures
The authors declare no conflict of interest.
Data availability
Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.
Supplemental document
See Supplement 1 for supporting content.
References
1. Y. Fu and T. Zhai, “Distributed feedback organic lasing in photonic crystals,” Front. Optoelectron. 13(1), 18–34 (2020). [CrossRef]
2. M. Karl, J. M. E. Glackin, M. Schubert, M. M. Kronenberg, G. A. Turnbull, D. W. Samuel, and M. C. Gather, “Flexible and ultra-lightweight polymer membrane lasers,” Nat. Commun. 9(1), 1525 (2018). [CrossRef]
3. M. T. Hill and M. C. Gather, “Advances in small lasers,” Nat. Photonics 8(12), 908–918 (2014). [CrossRef]
4. H. Fang, R. Ding, S. Lu, J. Yang, X. Zhang, R. Yang, J. Feng, Q. Chen, J. Song, and H. Sun, “Distributed feedback lasers based on thiophene/phenylene co-oligomer single crystals,” Adv. Funct. Mater. 22(1), 33–38 (2012). [CrossRef]
5. I. D. W. Samuel and G. A. Turnbull, “Organic semiconductor lasers,” Chem. Rev. 107(4), 1272–1295 (2007). [CrossRef]
6. A. Berdin, H. Rekola, O. Sakhno, M. Wegener, and A. Priimagi, “Continuously tunable polymer membrane laser,” Opt. Express 27(18), 25634–25646 (2019). [CrossRef]
7. C. Ge, M. Lu, X. Jian, Y. Tan, and B. T. Cunningham, “Large-area organic distributed feedback laser fabricated by nanoreplica molding and horizontal dipping,” Opt. Express 18(12), 12980–12991 (2010). [CrossRef]
8. B. Wenger, N. Tétreault, M. E. Welland, and R. H. Friend, “Mechanically tunable conjugated polymer distributed feedback lasers,” Appl. Phys. Lett. 97(19), 193303 (2010). [CrossRef]
9. J. Herrnsdorf, B. Guilhabert, Y. Chen, A. L. Kanibolotsky, A. R. Mackintosh, R. A. Pethrick, P. J. Skabara, E. Gu, N. Laurand, and M. D. Dawson, “Flexible blue-emitting encapsulated organic semiconductor DFB laser,” Opt. Express 18(25), 25535–25545 (2010). [CrossRef]
10. T. Zhai, X. Ma, L. Han, S. Zhang, K. Ge, Y. Xu, Z. Xu, and L. Cui, “Self-aligned emission of distributed feedback lasers on optical fiber sidewall,” Nanomaterials 11(9), 2381 (2021). [CrossRef]
11. T. Pudleiner, E. Sutter, J. Knyrim, and C. Karnutsch, “Colorimetric phosphate detection using organic DFB laser based absorption spectroscopy,” Micromachines 12(12), 1492 (2021). [CrossRef]
12. R. Muñoz-Mármol, V. Bonal, G. M. Paternò, A. M. Ross, P. G. Goj, J. M. Villalvilla, J. A. Quintana, F. Scotognella, C. D. Andrea, S. Sardar, G. Lanzani, Y. Gu, J. Wu, and M. A. Díaz-García, “Dual amplified spontaneous emission and lasing from nanographene films,” Nanomaterials 10(8), 1525 (2020). [CrossRef]
13. P. Zeng, Y. Zhou, B. Wang, X. Li, Q. Ou, X. Wu, and S. Zhang, “Nanoimprinted organic distributed feedback biosensors breaking the trade-off between sensitivity and threshold,” Org. Electron. 85, 105851 (2020). [CrossRef]
14. R. Steingrüber, M. Möhrle, and W. Fürst, “Continuously chirped gratings for DFB-lasers fabricated by direct write electron-beam lithography,” Microelectron. Eng. 61-62, 331–335 (2002). [CrossRef]
15. T. Zhai, F. Cao, S. Chu, Q. Gong, and X. Zhang, “Continuously tunable distributed feedback polymer laser,” Opt. Express 26(4), 4491–4497 (2018). [CrossRef]
16. G. Patrick, L. Marcus, K. Wolfgang, R. Thomas, and W. Sigurd, “Elastically tunable self-organized organic lasers,” Adv. Mater. 23(7), 869–872 (2011). [CrossRef]
17. D. Pisignano, L. Persano, P. Visconti, R. Cingolani, and G. Gigli, “Oligomer-based organic distributed feedback lasers by room-temperature nanoimprint lithography,” Appl. Phys. Lett. 83(13), 2545–2547 (2003). [CrossRef]
18. L. Wang, W. Liu, Y. Zhang, F. Qiu, N. Zhou, D. Wang, Z. Xu, Y. Zhao, and Y. Yu, “DFB LDs at DWDM wavelengths fabricated by a novel nanoimprint process for mass production and tolerance simulation,” Microelectron. Eng. 93, 43–49 (2012). [CrossRef]
19. C. Ge, M. Lu, W. Zhang, and B. T. Cunningham, “Distributed feedback laser biosensor incorporating a titanium dioxide nanorod surface,” Appl. Phys. Lett. 96(16), 163702 (2010). [CrossRef]
20. J. Viheriälä, K. Haring, S. Suomalainen, R. Koskinen, T. Niemi, and M. Guina, “High spectral purity high-power GaSb-based DFB laser fabricated by nanoimprint lithography,” IEEE Photonics Technol. Lett. 28(11), 1233–1236 (2016). [CrossRef]
21. T. Zhai, X. Zhang, Z. Pang, and F. Dou, “Direct writing of polymer lasers using interference ablation,” Adv. Mater. 23(16), 1860–1864 (2011). [CrossRef]
22. H. Fang, R. Ding, S. Lu, L. Wang, J. Feng, Q. Chen, and H. Sun, “Direct laser interference ablating nanostructures on organic crystals,” Opt. Lett. 37(4), 686–688 (2012). [CrossRef]
23. T. Zhai, Y. Wang, L. Chen, and X. Zhang, “Direct writing of tunable multi-wavelength polymer lasers on a flexible substrate,” Nanoscale 7(29), 12312–12317 (2015). [CrossRef]
24. W. Huang, Y. Liu, L. Hu, Q. Mu, Z. Peng, C. Yang, and L. Xuan, “Second-order distributed feedback polymer laser based on holographic polymer dispersed liquid crystal grating,” Org. Electron. 14(9), 2299–2305 (2013). [CrossRef]
25. S. J. Jang, J. S. Yu, and Y. T. Lee, “Laterally coupled DFB lasers with self-aligned metal surface grating by holographic lithography,” IEEE Photonics Technol. Lett. 20(7), 514–516 (2008). [CrossRef]
26. T. Zhai, Y. Wang, L. Chen, X. Wu, S. Li, and X. Zhang, “Red-green-blue laser emission from cascaded polymer membranes,” Nanoscale 7(47), 19935–19939 (2015). [CrossRef]
27. M. Hideki and F. Kenji, “Ordered metal nanohole arrays made by a two-step replication of honeycomb structures of anodic alumina,” Science 268(5216), 1466–1468 (1995). [CrossRef]
28. S. Liu, J. Tian, and W. Zhang, “Fabrication and application of nanoporous anodic aluminum oxide: a review,” Nanotechnology 32(22), 222001 (2021). [CrossRef]
29. O. Jessensky, F. Muller, and U. Gosele, “Self-organized formation of hexagonal pore arrays in anodic alumina,” Appl. Phys. Lett. 72(10), 1173–1175 (1998). [CrossRef]
30. G. E. Thompson, R. C. Furneaux, G. C. Wood, J. A. Richardson, and J. S. Goode, “Nucleation and growth of porous anodic films on aluminum,” Nature 272(5652), 433–435 (1978). [CrossRef]
31. Z. Su, G. Hähner, and W. Zhou, “Investigation of the pore formation in anodic aluminum oxide,” J. Mater. Chem. 18(47), 5787–5795 (2008). [CrossRef]
32. N. Kornelius, C. Jinsub, S. Kathrin, R. B. Wehrsphohn, and U. GÖsele, “Self-ordering regimes of porous alumina: The 10% porosity rule,” Nano Lett. 7(2), 677–680 (2002).
33. Z. Leszek, D. S. Grzegorz, and J. Marian, “Anodic alumina membranes with defined pore diameters and thicknesses obtained by adjusting the anodizing duration and pore opening/widening time,” J. Solid State Electrochem. 15(11), 2427–2436 (2011).
34. T. Zhai, X. Wu, S. Li, S. Liang, L. Niu, M. Wang, S. Feng, H. Liu, and X. Zhang, “Polymer lasing in a periodic-random compound cavity,” Polymers 10(11), 1194 (2018). [CrossRef]
35. P. Zhou, L. Niu, A. Hayat, F. Cao, T. Zhai, and X. Zhang, “Operating characteristics of high-order distributed feedback polymer lasers,” Polymers 11(2), 258 (2019). [CrossRef]
36. L. Han, C. Chen, J. Tong, L. Cui, and T. Zhai, “Manipulating the performance of polymer lasers using diffraction elements,” Org. Electron. 84, 105813 (2020). [CrossRef]
37. X. Shi, K. Ge, J. Tong, and T. Zhai, “Low-cost biosensors based on a plasmonic random laser on fiber facet,” Opt. Express 28(8), 12233–12242 (2020). [CrossRef]
38. T. Zhai, X. Zhang, Z. Pang, x. Su, H. Liu, S. Feng, and L. Wang, “Random laser based on waveguided plasmonic gain channels,” Nano Lett. 11(10), 4295–4298 (2011). [CrossRef]
39. G. D. Dice, S. Mujumdar, and A. Y. Elezzabi, “Plasmonically enhanced diffusive and subdiffusive metal nanoparticle-dye random laser,” Appl. Phys. Lett. 86(13), 131105 (2005). [CrossRef]
40. X. Meng, F. Koji, S. Murai, T. Matoba, and K. Tanaka, “Plasmonically controlled lasing resonance with metallic-dielectric core-shell nanoparticles,” Nano Lett. 11(3), 1374–1378 (2011). [CrossRef]
41. Z. Johannes, W. Christian, V. Cynthia, H. Calin, and A. K. Thomas, “Plasmonic nanostars as efficient broadband scatterers for random lasing,” ACS Photonics 3(6), 919–923 (2016). [CrossRef]
42. J. Zhang, F. Wang, S. Ghafoor, H. Wang, W. Zhang, K. Xie, R. Cheng, J. Yan, L. Niu, P. Wang, L. Zhang, and Z. Hu, “Tunable plasmonic random laser based on emitters coupled to plasmonic resonant nanocavities of silver nanorod arrays,” Adv. Opt. Mater. 10(10), 2200426 (2022). [CrossRef]
43. T. Zhai, F. Tong, F. Cao, L. Niu, S. Li, M. Wang, and X. Zhang, “Distributed feedback lasing in a metallic cavity,” Appl. Phys. Lett. 111(11), 111901 (2017). [CrossRef]
