Improved Pulsed Laser Operation with Engineered Nanomaterials

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Improved pulsed laser operation with engineered nanomaterials Ryan E. Latterman, Steven Birrell, Philip Ashley Sullivan, and Robert Allan Walker ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b03062 • Publication Date (Web): 08 Jul 2016 Downloaded from http://pubs.acs.org on July 9, 2016

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ACS Applied Materials & Interfaces

Improved pulsed laser operation with engineered nanomaterials Ryan E. Lattermana, Steven Birrellb, Philip A. Sullivana, Robert A. Walker*a a

Department of Chemistry and Biochemistry, Montana State University, Bozeman, MT

59717 b

Quantum Composers, Bozeman, Montana, 59717

KEYWORDS. Gold nanorods, amplified stimulated emission, Nd:YAG, stabilization, RAFT polymerization *email – [email protected] Abstract The power efficiency of a diode-pumped solid state laser was improved by encasing the Nd:YAG lasing medium with gold nanorod-doped epoxy. Gold nanorods where synthesized with a specific aspect ratio tuned to absorb at the Nd:YAG lasing wavelength of 1064 nm. The surfactant-stabilized nanorods in aqueous solution were then treated with a sequential, two step functionalization in order to improve nanorod solubility in organic solvents. This process required treating the gold nanorods with a thiol-containing polyethylene glycol (PEG) polymer followed by replacing the PEG-SH polymer with a multi-dentate thiol containing block co-polymer synthesized using RAFT synthesis. With a multi-dentate polymer, the nanorods were soluble in traditional epoxies that could be used to coat the outside of Nd:YAG rods. By absorbing excess lateral 1064 nm emission, the gold nanorod coating attenuates amplified spontaneous emission

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(ASE), a parasitic, incoherent process that limits power produced by Q-switch laser designs. Laser power increased by nearly two fold with addition of the 1064 nm absorbing gold nanorod coating. Gold nanorod epoxy coatings stand out as attractive materials for attenuating ASE by avoiding the fabrication difficulties of samarium oxide ceramics and the photostability limitations of organic dyes.

Introduction Designing a high efficiency diode-pumped solid state laser (DPSSL) requires optimization of many variables such as pumping geometry, resonator geometry, and cavity design. Higher efficiency translates into less needed input power, a smaller footprint, and ultimately application to a broader market. When considering the design of a Q-switched DPSSL, the absorption properties of the materials used can significantly affect its efficiency. Unwanted absorption at either the pumping or lasing wavelengths will limit the amount of useful energy available to the system. One of the most common DPSSLs emits at 1064 nm by pumping a neodynium-doped yttrium aluminum garnet (Nd:YAG) rod with an 808 nm diode laser. Significant emission at 1064 nm occurs laterally out of the laser rod and, when reflected back into the rod by the pump cavity, a parasitic phenomenon known as amplified spontaneous emission (ASE) occurs.1-8 ASE is incoherent and depletes the excited state population available for stimulated emission, reducing the efficiency of a Q-switched laser. This depletion can be inhibited by coating the laser rod in a material that is transparent at the pumping wavelength of 808 nm and highly absorptive at the lasing wavelength of 1064 nm. Coatings consisting of near-IR absorbing dyes are not practical because of their low


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solubility and high potential for photo-degradation. Experiments described in this work show how a Nd:YAG laser rod can be treated with a gold nanorod-doped epoxy. The thin film coating the outside of the laser rod allows for absorption and emission at the desired wavelengths with laser efficiency increasing by nearly two fold while circumventing the need for costly and complex fabrication alternatives. DPSSLs are employed in many industrial applications, but are not always designed with maximum portability and efficiency in mind. Increased efficiency translates into lower input power and reduces the need for a large power source. A smaller footprint allows DPSSLs to be used in situations and environments that otherwise would have been impractical. While not the only way to improve laser efficiency, reducing ASE is one strategy that directly improves performance without requiring largescale changes in instrument design or power electronics. Strategies to reduce ASE hinge on finding effective ways to coat or enclose the laser rod with a material that is selectively absorptive at one wavelength and transparent at another.6,7 Currently, one common material used to combat loss of efficiency through ASE is a samarium oxidedoped glass or ceramic.9,10 Yttrium, aluminum and samarium are incorporated into a glass or ceramic material that is then applied either on the surface of the gain medium or doped throughout the entire material. ASE is suppressed because Sm3+ has a sharp absorption centered at 1064 nm and is nearly transparent at 808 nm.

To produce a ceramic laser

rod, time-consuming slip casting and vacuum sintering techniques are required to incorporate the Sm-containing material into the lasing architecture.4 These materials are



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difficult to produce and the process of doping glass or ceramics requires specialized techniques and equipment. An alternative material that coats a laser rod and increases laser efficiency while at the same time lowering cost and effort of production would prove useful. Ideally, a laser rod coating would be simple to apply and process and the coating process itself could be performed at any time during the laser fabrication process. For example, a simple epoxy coating acting as a stable absorber would also have the added utility as an adhesive in the laser assembly process. The linchpin to this strategy is identifying an additive having the required optical properties. Organic molecules that absorb strongly at 1064 nm are known,11.12 but tend to be complicated to synthesize and have low solubility in common solvents. These molecules can also exhibit significant absorption at 808 nm, the typical pump wavelength of Nd:YAG DPSSLs. Additionally, photo degradation would also likely render these dyes unstable for long-term laser operation. An ideal material would offer ease of synthesis, be stable for long-term use, and be compatible with commercially available epoxy resins. Metallic nanoparticles stand out as attractive candidates for this application due to their high stability and unique optical properties that depend on size, shape and aspect ratio. Gold nanorods (GNRs) in particular have emerged as popular constructs for optical, sensing, and biomedical applications.13-15 As synthesis methods have improved, so too has the adoption of GNRs as unique optical absorbers.16,17 The high density of free electrons on the surface of GNRs allows for size and shape dependent surface plasmon resonances (SPR). These SPR resonances are discrete and generally quite narrow (~200


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nm). GNRs have two distinct SPR modes: longitudinal and transverse, resulting from their length and width, respectively. The transverse SPR (TSPR) absorbs near 500 nm, while the longitudinal SPR (LSPR) varies depending on the length of the GNR. Synthesis of pure GNRs having tunable and narrow distributions in aspect ratios permits access to both the visible and near-IR regions of the electromagnetic spectrum. In this work, GNRs were synthesized and functionalized with custom polymers in order to produce thermally stable epoxy coatings that absorb at 1064 nm and are transparent at 808 nm with the goal of increasing efficiency, ease of production, and lowering the cost of DPSSLs.

Experimental Section Synthesis of gold nanorods. Gold nanorods were synthesized using a modified seed synthesis developed by Ye et al.18 The seed solution was prepared by mixing 5 mL of 0.5 mM HAuCl4 ·3H2O with 5 mL of 0.2M cetyltrimethylammonium bromide (CTAB). 0.6 mL of freshly prepared 0.01M NaBH4 was diluted to 1 mL and injected into the HAuCl4-CTAB solution while stirring vigorously for 2 minutes. The solution turned from yellow to brown. Before use, it was allowed to age for 30 minutes at slightly above room temperature. If temperature was not elevated, crystallization of CTAB was observed. A growth solution was prepared by fully dissolving 7.0 g of CTAB and 1.234 g Sodium Oleate in 250 mL of ultrapure water while stirring at a temperature of ~50 °C. After cooling to 30 °C, 24 mL of 4 mM AgNO3 was added and kept undisturbed at 30 °C for 15 minutes. 250 mL of 1 mM HAuCl4 ·3H2O was then added and stirred for ~45



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minutes until the solution’s color changed from yellow to clear. The pH was then adjusted by the addition of 3.6 mL concentrated HCl. After 15 minutes of slow stirring, 1.25 mL of 0.064M Ascorbic Acid was introduced and stirred vigorously for 30 seconds.

Figure 1. Synthesis of gold-reactive polymer using the RAFT technique. Pentaflouro methylmethacrylate is a stable monomer that is replaced with a thiol containing functional group after polymerization.

400 µL of seed solution was then injected into the growth solution and stirred for 30 seconds. The solution was left undisturbed at 30 °C for 12 hours. The color of the resulting nanorod solution was light brown, indicative of very few spherical impurities. Absorption spectra and transmission electron micrograph images and are found Figures S1 and S2, respectively.


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Functionalization of gold nanorods. The functionalization procedure was adapted from Thierry et al.19 168 mL of freshly prepared GNRs were centrifuged at 6000 rpm in 14 mL falcon tubes for 1 hour. The clear supernatant was discarded and the GNR pellets were resuspended in 1.5 mL of water and centrifuged for 10 mins at 13,000 rpm.

mPEG-SH replaced by multi-dentate thiol polymer in THF solution

CTAB replaced by mPEG-SH in aqueous solution

SH N

N

N

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N

CTAB bilayer

O

SH O

O

O

NH

O

N

n

SH

m

mPEG-SH

l

Multi-dentate thiol polymer

Figure 2. Gold nanorod functionalization. Gold nanorods are synthesized in an aqueous environment stabilized by a CTAB bilayer. The CTAB can be replaced by a solution of MPEG-SH at which point they are soluble in organic solvents like THF. The mPEG-SH is then replaced by a multi-dentate thiol polymer to produce GNRs that are soluble in organic solvents and UV-curable epoxy.

the resulting pellets were resuspended in 6 mL of water and placed in a 14 mL falcon tube. 6 mL of aqueous 1 mg/mL Methoxy-Poly(Ethylene-glycol)-Thiol, 5000 average MW, (mPEG-SH) was added to the GNRs while vigorously shaking followed by sonication for 5 minutes. The resulting solution was left to react at room temperature



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overnight. Excess mPEG-SH solution was removed by centrifugation for 10 minutes at 13,000 rpm. The pellets could then readily be resuspended in organic solvents such as THF and acetone. No color change or precipitation was observed after resuspension. THF solutions of GNRs were then mixed with 5 mg/mL equivolume solutions of thiolfunctionalized polymer in THF, sonicated for 90 minutes and left to react overnight. Excess polymer solution was removed by centrifugation at 13,000 rpm for 10 minutes. GNR pellets were redispersed in 4 mL of THF. Typically, an epoxy coating contained 0.015 mL of concentrated GNRs in THF and 0.110 g of epoxy. Synthesis of Gold-Reactive Di-block copolymers. Thiol-containing goldreactive polymer was synthesized using the RAFT technique. Experimental details and characterization are found in the Supporting Information.

Results and Discussion The most common method of synthesizing GNRs is the surfactant based seedmediated method.20,21 GNRs synthesized with this method are only stable in an aqueous environment. In order to use GNRs in an epoxy coating, their surface must be coated with a compound that is compatible with organic environments. Aqueous GNRs have been successfully functionalized with a variety of thiol-containing compounds including cationic species,22,23 porphyrins,24 pseudorotaxanes,25 perylenes26, water soluble diblockcopolymers27, and others.28-31 Some methods are more complex than others, but the one chosen here uses a relatively simple two-step process.19 Thiol-terminated methoxy polyethylene glycol (mPEG-SH) serves as an intermediate stabilization layer that makes the nanoparticles soluble in both water and in organic solvents. The mPEG-SH


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functionalized nanoparticles are then dispersed in a solvent such as tetrahydrofuran and left to react with solutions of a thiol-terminated compound of choice. These steps are illustrated schematically in Figures 1 and 2. In this work, gold nanorods were rendered organic-soluble by using thiolfunctionalized diblock copolymers synthesized by the RAFT (Reversible Addition/Fragmentation Chain Transfer) technique.32, 33 The RAFT polymerization technique was chosen in order to easily access a diblock polymer that provides a highly organic-soluble block, poly(methyl methacylate), and a polydentate anchor block that binds strongly to the GNR surface. The synthesis of the gold-reactive polymer is shown in Figure 1. First, methyl methacrylate was polymerized using azobisisobutyronitrile (AIBN) as the radical initiator and 2-cyano-2-propyl dodecyl trithiocarbonate as the RAFT agent. This first block of PMMA was not used to bind to the gold nanorod but rather as a block that contributes to high solubility in organic environments. After polymerization, this PMMA block retained the RAFT active trithiocarbonate termination allowing it to act as a macroinitiator for further polymerization with a second monomer. Pentafluorophenyl methacrylate was then polymerized with the PMMA macroinitator to introduce the second, reactive, polymer block. Pentafluorophenyl methacrylate was chosen because of its stability during polymerization and its susceptibility to postfunctionalization via amine-selective nucleophilic substitution.34-36 After isolating the PMMA-co-PPFMA diblock, treating it with cysteamine produced the gold-reactive diblock copolymer, shown in Figure 1, as the final product.



Typically, GNRs were prepared at a 500 mL scale using methods adapted from Ye et al.18 168 mL of freshly prepared GNRS were used as one batch for functionalization. Excess CTAB, sodium oleate and other reactants were removed by centrifugation. After centrifugation, the supernatant containing undesired reactants was 1.4 1.2

Absorbance (au)

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GNRs in N65

1

GNRs in THF

0.8 0.6 0.4 0.2 0 400

600

800

1000

1200

1400

Wavelength (nm)

Figure 3. Absorption spectra of GNRs in THF solution compared to that of a GNRdoped Norland 65 epoxy film with the same thickness used in the fully assembled laser described in this work (0.0254 mm). The distinctive absorption profile of GNRs is maintained throughout the functionalization process. The LSPR peak exhibits a bathochromic shift after incorporating into Norland 65 epoxy but still exhibits high absorption at 1064 nm.

carefully removed and each pellet of GNRs was redispersed in 1 mL of deionized water, centrifuged again and redispersed in a total of 6 mL of water. This highly concentrated solution of GNRs was used in the next reaction step without further purification. Additional centrifugation cycles were avoided as any more would reduce the residual CTAB concentration below the threshold for GNR stability.37 6 mL of a 1 mg/mL solution of thiol-terminated polyethylene glycol (5000 molecular weight) in water was prepared and added to a 14 mL falcon tube containing 6 mL of highly concentrated


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GNRs. After brief mixing and sonication, the mixture was allowed to react at room temperature overnight. The literature called for a reaction time of a few hours, however, we found that an overnight reaction produced GNRs that were more consistently stable in organic solvents. After reacting overnight, the GNRs were purified by centrifugation and could then be redispersed in organic solvents. Although initially stable in organic solvents, mPEG-SH coated GNRs were observed to precipitate out of solution after a week at room temperature. Therefore, these THF solutions of GNRs were immediately added to equivolume 5 mg/mL solutions of the multi-dentate thiol-containing polymer shown in Figure 1. After 90 minutes of sonication, the solutions were left to react overnight at room temperature and then purified by centrifugation. The absorption spectrum of GNRs coated with a multi-dentate thiol polymer in acetone was collected many months after synthesis and is shown in Figure S3. No shape deformities can be seen in the spectrum and no precipitated GNRs were observed in the vial. The lack of precipitation indicates that GNRs coated in multi-dentate thiolcontaining polymers are stable in organic solvents for long periods at room temperature. Figure 2 depicts the functionalization process where the aqueous CTAB environment surrounding the GNRs is replaced with a multidentate thiol-polymer coating. Organic solutions of these GNRs were compatible with solutions of polymers or epoxies and were demonstrated to be easily applied to multiple surfaces using casting or spin coating techniques. Figure 3 shows the absorption spectra of GNRs in a film of Norland 65 epoxy compared to GNRs in a solution of THF. After normalizing with respect to the



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LSPR peak, a high absorption is still observed at 1064 nm and the distinctive GNR absorption profile is still intact. Thermogravimetric analysis (TGA) was used to confirm that the mPEG-SH coating had been replaced by the multi-dentate thiol polymer. As GNRs were heated, the compounds adhered to their surface decomposed leaving bare gold in the sample pan. The resulting thermogram displays weight loss percentage versus temperature. This weight loss curve is unique to the different GNR surface compositions. To prepare samples for TGA experiments, 1 mL of highly concentrated GNRs were centrifuged and the supernatant discarded. The resulting pellet was redispersed in 50 microliters of solvent before being added slowly in 5-10 microliter portions to an aluminum pan. The solvent (either aqueous or organic) was evaporated by using a flow of nitrogen gas before another portion was added. A photo of TGA sample preparation is found in Figure S4. After the desired amount of portions were added, the pan was placed under vacuum for 1 hour. Using this method, enough GNR weight was added to ensure a successful TGA measurement. Because GNRs are stabilized in solution by CTAB during and after synthesis, we expected to see weight loss near a similar temperature to that of a sample of pure CTAB in the TGA thermogram. Figure 4a shows the TGA thermogram of pure CTAB and GNRs after they have been synthesized. Weight percentage begins to decrease near 200 °C for both CTAB and the GNRs. These results confirm the presence of CTAB on the surface of the GNRs before any functionalization with thiol compounds. After reacting


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with mPEG-SH, TGA experiments were again performed with an expectation that the weight loss vs. temperature profile would mirror that of pure mPEG-SH. Figure 4b shows a typical TGA thermogram of GNRs after reacting with mPEG-SH along with thermograms of pure CTAB and pure mPEG-SH. If any significant amount of CTAB remained on the surface of the GNRs, an obvious weight loss near 200 °C would be observed. As seen in the TGA thermogram the most significant weight loss is observed near 350 °C indicating the GNRs have been functionalized with mPEG-SH. After GNRs were functionalized with mPEG-SH, they were reacted with the multidentate thiol polymer shown in Figure 1. TGA was used to determine whether the weight loss profile changed after the reaction took place. Figure 4c shows the TGA traces of GNRs coated in mPEG-SH and coated in multidentate thiol polymer. These data are distinctly different from the nanorods coated with mPEG-SH. A gradual weight loss profile is seen for the sample of GNRs coated in multi-dentate thiol polymer. The distinctive drop in weight near 350 °C characteristic of mPEG-SH coated GNRs is no longer observed after a reaction with the multi-dentate thiol polymer. These data indicate that the surface of the GNRs is no longer coated in mPEG-SH.



101 100

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Weight, %

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Weight, %

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98 97 96

GNRs coated in multidentate thiol polymer

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GNRs coated in mPEG-SH 94

mPEG-SH

93 92 0

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Figure 4. TGA thermograms of gold nanorods. a) Thermogram of CTAB and GNRs coated in CTAB b) Thermogram of GNRs coated in mPEG-SH; pure mPEG-SH and CTAB included for reference. c) Thermogram of GNRs coated in multidentate thiol polymer compared to GNRs coated in mPEG-SH; pure mPEG-SH included for reference.


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Fluorescence of GNR Coated Nd:YAG After confirming that the surface of GNRs had been coated in an organic-soluble polymer, mixtures of Norland 65 epoxy were prepared with varying amounts of THF solutions of poly-thiol functionalized GNRs. A highly concentrated solution of GNRs in THF was used to ensure only a small volume was needed to dope the epoxy. In order to simulate the conditions of a production model laser, a Nd:YAG rod was end-pumped with the 808 nm laser diode that would be used in a production model DPSSL. Using an Edmund Optics CMOS camera fitted with a 1064 nm filter, images of 1064 nm fluorescence were obtained perpendicular to the pump direction. Figure 5 shows the dramatic decrease in 1064 nm intensity after the laser rod is coated with GNR doped epoxy. Optimization of coating conditions lead to a typical coating that contained 0.015 mL of concentrated GNRs in THF and 0.110 g of epoxy. This coating consistently absorbed ≥70% of the 1064 nm fluorescence as detected by the camera using a concentration of GNRs of 3.1× 10-8 M.



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Figure 5. Fluorescence images at 1064 nm of a Nd:YAG laser rod pumped at 808 nm. Top left: coated in 0.0127 mm of un-doped epoxy. Top right: coated in 0.0127 mm of GNR-doped epoxy. Bottom middle: coated in 0.0254 mm of GNR-doped epoxy. Obvious suppression of 1064 nm fluorescence is observed after coating in GNR-doped epoxy.

After coating the Nd:YAG rod with the GNR containing epoxy, the laser components were fully assembled and output efficiency was tested. A photo and schematic of the laser assembly are found in found in Figure S5. Figure 6 shows a significant increase in output energy after the laser rod is coated in GNR doped epoxy. Without the GNR epoxy coating, the laser output levels off near 8 mJ. With the GNR coating, output energy reaches 15.14 mJ. In an uncoated Q-switched DPSSL a significant amount of 1064 nm fluorescence reflects back into the laser cavity which


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stimulates emission from the excited state prematurely. This premature excitation limits the maximum output power that a Q-switched laser can achieve. The laser used in this work is designed to operate continuously at a maximum temperature of 35 °C. Studies have shown that GNRs significantly deform at 100 °C and above.38, 39 The GNRs used in this work were heated for 2 days at 100 °C and showed no significant change in absorption profile. Additionally, Figures S6 and S7 show transmission electron microscope images and absorption spectra of GNR films acquired before and after heating for 5 days at 60 °C. No size or shape deformation was observed, indicating that the GNRs are stable past the intended operating temperature.

16 14

Output Energy (mJ)

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12 10 8 6

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Input Energy (mJ)

Figure 6: Laser Efficiency with and without GNR coating. The uncoated rod output energy rolls off in a simple Q-switch resonator due to the increase in ASE losses as the gain is increased. The roll-off in the coated rod has increased significantly allowing more stored energy and greater output energy.

In order to test the long term stability of these films, a Nd:YAG rod coated with the GNR-containing epoxy was used to construct a DPSSL test unit that was aligned,



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purged with dry nitrogen and then sealed. The unit was subjected to an accelerated aging procedure where a baseline stability measurement of 2000 shots was made followed by acquisition of an input-output curve similar to that shown in Figure 6. The laser was then subjected to a 24 hour thermal cycle consisting of two heating ramps from 25˚C to 50˚C and back that included a two hour dwell at each extreme. Following each cycle, shot-toshot stability and I/O curves were again measured (at 25˚C). This thermal cycle was repeated six times and the results are summarized in Figure 7 and Table 1.

Figure 7: Lasing stability of GNR epoxy coated Nd:YAG rods. a) Trace of laser output energy vs. laser input energy (I/O) following the conclusion of the first and sixth thermal cycles. The baseline trace prior to any cycling is included underneath the two postthermal cycling traces. Error bars reflect the standard deviation of measured output energies over all six cycles. b) Shot-to-shot stability following thermal cycles 1 and 6.


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The data show that both shot-to-shot stability and I/O performance did not suffer as a result of thermal cycling. Depending on the application, typical operating temperatures for these DPSSL lasers are ≤ 35˚C, so the thermal cycling marked conditions that were considerably more extreme than what the unit will experience during standard usage. Furthermore, we note that the GNR epoxy coating has been applied in more than 20 DPSSL units installed worldwide and have operated 24/7 for more than a year with an estimated total shot count of more than 2 x 109 without any reported failures due to the GNR coating.



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Table 1. Effects of thermal cycling on lasing performance Input/Output Input energy (mJ)

111 119 127 134 142 150 158 166 174 182 Shot to Shot stability (2000 shots) Baseline Post-thermal 1 Post-thermal 3 Post-thermal 6

Baseline (mJ)

Post-thermal 1 (mJ)

Post-thermal 6 (mJ)

Average (mJ) all trials

St. Dev. (mJ) all trials

2.28 3.54 4.94 6.63 8.51 10.43 12.18 13.98 15.58 17.16

1.63 3.40 4.82 6.55 8.44 10.30 12.11 14.03 15.58 17.00

1.93 2.97 4.17 5.79 7.73 9.69 11.62 13.46 15.27 17.26

1.92 3.08 4.35 5.93 7.80 9.65 11.58 13.36 15.02 16.71

0.20 0.28 0.38 0.47 0.49 0.53 0.47 0.57 0.56 0.49

Mean output energy (mJ)

St. Dev (mJ)

% Deviation

16.9 16.9 16.3 16.9

0.12 0.12 0.09 0.14

0.7 0.7 0.6 0.9

Table 1. All measurements were performed using a GNR epoxy coated Nd:YAG rod in a commercially manufactured DPSS laser (JEWEL manufactured by Quantum Composers).

Conclusions The materials produced here offer a simple and versatile solution to the problems caused by amplified spontaneous emission. Combining GNRs with a commercially available optical adhesive allows for increased efficiency and aids in the laser production process. Because Nd:YAG lasers are used in a wide variety of industrial and research atmospheres, the implications of this effective GNR coating are therefore highly impactful and far-reaching. This work focused on DPSSLs that operate at 1064 nm.


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However, since the absorptive properties of GNRs can be tuned by simply changing their size, films absorbing at a variety of wavelengths can be produced and applied to the laser system of choice. GNR doped epoxy can also be a versatile tool for any application where a tunable absorber is required, provided that the operating temperature is at or below 100 °C.

Associated Content Laser diagrams, TEM images of GNRs, RAFT polymer synthesis details, and additional figures are found in the Supporting Information. This material is available free of charge via the Internet at http://pubs.acs.org.

Acknowledgements. REL and PAS gratefully acknowledge support from the Army Research Office (Grant No. W911NF-12-1-0333). RAW acknowledges support from Montana’s Research and Economic Development Initiative (M-REDI). The authors thank Dr. Jim Driver from the University of Montana for assistance with TEM characterization.



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Table of Contents Figure Lateral 1064 nm Fluorescence

16 14

Polarizer & wave plate Output coupler

Prism

Prism

1064 nm output

No Coating Prism

With GNR Coating

EO Q-switch

808 nm input

Output Energy (mJ)

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12 10 8 6

Coated with GNRs

4

GNR-doped epoxy coating

2

Nd:YAG Lasing Medium

0

Uncoated

120

140

160

180

200

Input Energy (mJ)


220

240

Improved Pulsed Laser Operation with Engineered Nanomaterials

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