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Abstract
Large aperture periodically-poled Rb:KTP crystals designed for optical parametric amplifiers in 2 µm LIDAR systems were radiation hardness tested by exposure of proton beams at 10 MeV and 60 MeV energies. An irradiation dose of 55 Gy was used to commensurate the crystals’ estimated exposure on board a mission in the low-Earth orbit. The irradiation effects were investigated by comparing optical transmission spectra and 2D effective nonlinearity mapping in a 2 µm OPO setup before and after irradiation. The results reveal that the periodically poled structure remained intact after irradiation, and the changes in the optical transmission and nonlinear properties were close to the measurement uncertainty. This investigation is essential for realizing efficient frequency converters for space applications, such as spaceborne active greenhouse gas monitoring LIDAR instruments or correlated photon-pair sources.
© 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. Introduction
Accurate monitoring of greenhouse gas (GHG) concentration distributions, e.g., CO2, CH4, HDO, and H2O in atmospheric columns, is important for reducing uncertainties in climate modeling [1,2]. These gases have rotational-vibrational fundamental and overtone absorption bands in the near to mid-IR region (1.5-3.7 µm) and can be accessed by differential absorption LIDAR systems (DIAL) based on parametric down-conversion. The GHG column concentration mapping is best achieved by airborne and spaceborne DIAL systems. Typically, such systems contain high-energy, wavelength-agile, narrow-linewidth coherent sources in the GHG fingerprint spectral region. Active sensors considered for low-Earth orbit (LEO) deployment, such as MERLIN methane integrated path DIAL [3,4] and the multispecies DIAL, currently under development [5], are using, for the emitter, optical parametric oscillators (OPO) and parametric amplifiers (OPA) to deliver high energy nanosecond pulses. OPOs and OPAs employing periodically-poled nonlinear crystals, e.g., PPKTP and PPLN, offer high nonlinearity, noncritical phase matching, and sufficiently large gain bandwidth to support a rapid wavelength-hopping operation as required for DIAL emitters [5,6]. The large optical aperture [7,8] possible with Rb:PPKTP [9] and its high optical damage threshold allow for OPA output energy scaling to tens of mJ in the 1.5 µm -3 µm spectral region, while pumping with well-established 1.064 µm Q-switched lasers. PPKTP is also desirable for realizing spaceborne entangled photon sources using spontaneous parametric down-conversion (SPDC), replacing the BBO crystals used in the first generation of satellite-borne quantum optical experiments [10–12]. Additionally, the ferroelectric domain structuring technology for Rb:PPKTP has attained high precision today, enabling the fabrication of sub-µm periodicity structures needed to realize backward-wave optical parametric oscillators [13]. These devices offer precise tuning in a simple, mechanically robust arrangement without the need for external optical cavities. They can generate mJ-level nanosecond output pulses with high efficiency [14], thus being suitable as seed sources for OPA power stages in future spaceborne LIDAR emitters.
The reliable operation of nonlinear optical devices in space requires the materials and structures to retain functionality under the typical radiation environment throughout the mission duration. Therefore, radiation hardness testing is mandatory for all new materials introduced into the onboard systems. Solar emission protons trapped in the Earth's radiation belts, high-energy particles originating from galactic cosmic rays, and gamma radiation represent primary sources of persistent radiation in low-earth orbit (LEO). These need to be considered in optical systems operating under the onboard protection provided by satellite shielding [15,16].
A potential weakness of the optical materials most used for QPM and operating under the abovementioned conditions lies in their ferroelectric nature. To achieve phase matching in periodically poled ferroelectrics, such as Rb:PPKTP, the second-order nonlinearity is structured by periodically reversing the direction of spontaneous polarization in the crystal. Such a phase transition process involves an injection of sub-surface charge in the crystal to create the electric field exceeding the coercive field. Ionizing radiation-induced charging caused either by direct charged-particle deposition primarily due to proton irradiation or internal ionization cascades caused by protons or gamma rays [17] can potentially induce modifications in the ferroelectric domain structure, detrimental for the QPM device performance. The second effect, which could degrade nonlinear crystal performance in the LEO environment, is related to the creation of color centers that absorb optical radiation [18]. This effect is similar to the blue and ultraviolet light-induced absorption centers associated with photoexcited carriers trapped near lattice defect sites [19]. The third process is the induced radioactivity due to nuclear reactions with high-energy protons [20]. The radioactive emissions could become a source of further damage and lead to transmutation and chemical changes.
The impact of proton and gamma radiation on single domain KTP and so-called gray-track resistant KTP has been investigated previously using measurements of linear optical transmission and second harmonic generation from 1.064 µm [21,22]. We have previously reported on the effects of gamma radiation in KTP, Rb:KTP, and Rb:PPKTP structures [18]. Rb:PPKTP is less susceptible to laser-induced color center formation than periodically-poled structures fabricated from undoped flux-grown KTP [19]. KTP and Rb:KTP showed a marginal decrease in transmission in the spectral region between 400 nm and 600 nm after gamma irradiation, although the radiation effects on Rb:KTP were somewhat weaker [18]. The transmission could be fully recovered after a thermal annealing step. Previous reports on the susceptibility of single domain KTP crystals to proton radiation seem inconclusive. Reference [21] reported a substantial decrease in optical transmission over the whole measured spectral range between 350 nm and 1000 nm, following irradiation with protons at 10.8 MeV, 100 MeV and 230 MeV energies. On the other hand, Ref. [22], using several times higher proton fluence and similar proton energies, reported much lower linear transmission change and no measurable difference in the SHG efficiency. To the best of our knowledge, the effect of proton radiation on the periodically poled structures in Rb:PPKTP has not been reported so far.
In this work, we investigate the effect of proton radiation on the performance of large optical aperture Rb:PPKTP crystals. The crystals were designed for high-energy OPA in the 2 µm spectral range, appropriate for the application in the airborne and spaceborne LIDAR instruments for GHG measurements [5]. The linear transmission and the performance of Rb:PPKTP in the OPO setup were investigated before and following the irradiation with 10 MeV and 60 MeV energy protons. The irradiation protocol was designed to correspond to the expected integrated proton fluence over a 5-year long mission in LEO.
2. Experiment
2.1 Irradiation conditions
Low-Earth orbit is loosely defined as spanning altitudes between 200 km and 2000km, approximately to the inner edge of the Van Allen radiation belt. The orbit-integrated radiation flux depends on orbit parameters such as altitude, inclination, eccentricity, and, due to solar activity cycles, the specific time when the mission is operational [23,24]. Extensive experimental dosimetry has been deployed over decades on LEO satellites, and the data has been used to build current theoretical predictive models for expected exposure, including proton radiation. ISO 15856 standard [25] specifies the computational platform called Space Environment Information System (SPENVIS) [26], maintained by ESA as a simulation tool for predicting radiation exposure in orbit as well as the effects of such radiation. Specifically, for proton radiation, the models AP-8 and AP-9 [27] are specified in SPENVIS. AP-8 is an older proton irradiation in the space environment model, originally introduced by NASA, while a broad collaboration of stakeholders developed the updated model AP-9, exploiting new data sets, and publicly released in 2012 [27]. The modeling shows that the protons trapped by the Earth's magnetic field are the main contributors to the proton-related total irradiation dose in the LEO [28,29]. For instance, for a circular orbit at an altitude of 590 km and an inclination of 29°, a 5-year mission launched in 2001 would have experienced the integral proton fluence of about 3 × 1010 p+/cm2 for energies above 1 MeV [29]. The proton fluence decreases steeply for the energies exceeding 100 MeV. A similar proton fluence (1.4 × 1010 p+/cm2) was estimated for a 5-year mission in circular orbit at an altitude of 800 km, using the SPENVIS modeling environment [28]. The satellite platforms include appropriate shielding of the electronic and active optical equipment to mitigate the effects of ionizing radiation. The metal Al-shielding is highly effective against free-electron radiation and protons with energies below 50 MeV. It is less effective against the higher energy protons, however. Simulations show that the total dose acquired by the components behind the 5-mm Al-shield would be dominated by the high-energy proton irradiation [28,30]. For instance, the fluence of protons with an energy of 10 MeV would decrease by about two orders of magnitude with such Al-shielding, while the fluence of protons with the energy of 100 MeV would be hardly affected at all [30].
Interaction of high-energy protons with dielectrics gives rise to several effects of importance to the functioning of optical components. Mainly these are: (1) displacement damage (DD) due to elastic scattering, (2) ionization-mediated inelastic scattering, and (3) fractionalization of the target nuclei and emission of secondary particles such as neutrons, a-particles, and g-photons [31]. As a result of the third process, the material, after irradiation, could become radioactive. The main detrimental processes, namely DD and ionization, take place at different proton energy scales, allowing treating them phenomenologically as separate. The displacement interaction is the leading cause of damage in dielectrics for proton energies below 1 MeV. For the energies higher than 10 MeV, the ionization effects will dominate the total radiation dose. The cumulative radiation dose is calculated by multiplying the so-called stopping power (SI units of Jm2kg−1) by the integral proton fluence expected during the mission period. The stopping power represents the proton energy loss per unit propagation length in a particular material. In the radiation hardness characterization, the total radiation dose for a given proton fluence is customarily given in the equivalent dosage in Si. This relates to Si being a simple material with well-known radiation hardness properties. The relevant parameters for calculation are the material density and the mean excitation energy, which for Si are 2.33 g/cm3 and 173 eV, respectively. For estimating the cumulative dose in KTP, we used a material density of 3.01 g/cm3 and the mean excitation energy of 144 eV. The mean excitation energy was derived from KTP molecular composition and elemental mean excitation energies by using Bragg's additivity rule [32–34]. This rule provides an estimate for the mean excitation energy using proton irradiation when empirical data for a compound is not available [35]. In terms of proton stopping power, KTP has similar properties to Aluminum oxide (mean excitation energy of 145 eV and density of 3.97 g/cm3) and CaF2 (mean excitation energy of 166 eV and density of 3.18 g/cm3), two materials for which empirical data and models exist [36]. Figure 1 shows the total cumulative dose of the radiation (1Gy = 0.1 krad) after irradiation with protons at different energies with the fluence of 1010 p+/cm2. The doses were calculated using the PSTAR model maintained by NIST [36]. Due to the above-mentioned shielding effect from the satellite structure, the proton energies between 10 MeV and 100 MeV are relevant for practical applications. Figure 1 shows that the total dose in Si for the pertinent region would be very close to the doses in the materials with properties similar to KTP.
Fig. 1. Calculated total cumulative radiation dose for the proton energies and the total fluence of 1010 p+/cm2 in Aluminum Oxide (red line), CaF2 (blue line), and Si (black line).
The SPENVIS model calculations for LEO show that the expected radiation dose in Si over a 5-year mission would be about 55 Gy for Al-shielding above 5 mm [28]. That corresponds to the proton fluence of 1010 p+/cm2 at the proton energy of 10 MeV and 4 × 1010 p+/cm2 at 60 MeV. These energies and fluences were used for irradiation of Rb:PPKTP samples. The irradiation parameters are similar to those recently used for testing the radiation hardness of 2 µm Ho:YLF laser-based LIDAR components [37].
The irradiation of the samples was done in the UC de Louvain proton cyclotron facility. The available proton beam energy was between 10 MeV and 60 MeV, with the FWHM of 5 MeV. The proton energy was controlled by using calibrated energy degraders. The facility provided proton flux of 108 p + cm−2s−1 at 60 MeV and 6 × 107 p + cm−2s−1 at 10 MeV. The exposure time was adjusted to achieve the same equivalent cumulative dose of 55 Gy at both energies. The Rb:PPKTP samples under irradiation were placed directly in the center of the 80 mm diameter proton beamline without additional shielding. The proton beam was propagating along the crystal polar axis, where the deposition of space charge can lead to modification of the ferroelectric domain grating structure.
2.2 Optical testing procedures
Three Rb:PPKTP samples were used in the experiment, of which, one sample was not irradiated and kept as a reference. To avoid possible effects from the irradiation on coatings or the coating-crystal interfaces the crystals were kept uncoated. Generation of parametric radiation in the GHG region (signal 1.5-2.1 µm and idler 2.1-3.7 µm) using pumping by a Nd:YAG laser at 1.064 µm, requires Rb:PPKTP crystals with grating periods in the range of 34-39 µm. All crystals were periodically poled with a 38.75 µm period for type-0 conversion from 1.064 µm to 1.98 µm (signal) and 2.30 µm (idler) at 60 °C. The 16 mm long Rb:PPKTP crystals had gratings with an optical aperture of 5 × 5mm2 and length of 12 mm.
The optical transmission spectra of the samples before and after irradiation were measured by Lambda 1050 Perkin-Elmer spectrophotometer. The nonlinear optical performance of the crystals was evaluated using a singly-resonant OPO setup, schematically shown in Fig. 2. In the figure, the crystal's crystallographic a, b, and c axes are along the lab x, y, and z axes, respectively. The OPO cavity was semi-hemispherical, with a length of 26.1 mm with an input mirror ROC = 150 mm. Both mirrors were transparent for the pump, the input was HR coated both the signal and the idler wave, and, the output mirror was partly reflective at the signal (50%) while it transmitting the idler. The pump beam distribution was measured along the cavity axis by scanning with a CCD camera (Thorlabs CAM-01) and fitting the result to a Gaussian propagator. Calculations using the measured profile showed that the 1/e2 pump beam radius was 350 µm inside the Rb:PPKTP crystal.
Fig. 2. The OPO cavity used for characterizing Rb:PPKTP. The idler and signal are detected using a dichroic mirror. A mechanical stop is used to reference the crystal position.
The pump laser was an injection-seeded, Q-switched Nd:YAG laser (InnoLas Laser GmbH) working at a pulse repetition rate of 100 Hz, with a maximum output energy of 200 mJ (<1% instability), and it was polarized along the z-direction with a pulse-width of 10.8 ns (FWHM). Pump input and depleted pump, as well as the OPO power were measured as a function of pump power. The crystal could be translated in the y- and z-direction for measuring OPO performance (OPO threshold and output powers) across the optical aperture. A mechanical stop was used for referencing crystal absolute position along the y-direction. With the edge of the mount we referenced the crystal position along the x-direction. This geometrical referencing allowed us to compare 2D OPO threshold maps before and after irradiation.
An OPO threshold measurement is a good measure of the quality of the poled samples. It can be used to determine the crystal's effective nonlinear coefficient (deff). The threshold equation for a singly resonant OPO operating in a nanosecond pulse regime can be used to extract the coefficient using the equation [38],
3. Results and discussion
A microscope image in Fig. 3(a) of the selectively chemically etched originally un-patterned [7] polar surface of the 5-mm thick Rb:PPKTP shows that the ferroelectric domain structure propagated throughout the 5 mm crystal thickness. The measured OPO output energies in the three samples used for proton irradiation testing are shown in Fig. 3(b). The typical efficiency at 2.6 mJ of the input pump energy reached 40%. The error is estimated to 0.05 mJ along x-axis (pump), while the OPO output error bar represents the rms of output power variation over 60 seconds at each pump power level measured by a power meter (Gentec-EO UP19K-15S-H5-D0 and Gentec MAESTRO). For the purpose of the measurement of the effective nonlinearity, we restricted pump intensity to the linear part of the OPO power dependence. A linear fit was used to extrapolate the pump energy at the OPO threshold, and Eq. (1) was employed to extract the effective nonlinear coefficient deff. After the threshold was measured, the pump was kept constant at 1.6 mJ, and the entire optical aperture was 2D-scanned in steps of 0.4 mm, i.e., a step size similar to the beam radius. This procedure constructed a two-dimensional map of the local signal and idler output energies at a constant pump energy. Variations of the measured OPO power across the optical aperture could be then attributed to the differences in the quality of the structure and thus to the variations in deff.
Fig. 3. (a) Microphotograph of the selectively etched polar surface of the un-patterned c + -side. The domain period is 38.75 µm. (b) The measured OPO power characteristics for the three Rb:PPKTP samples (before and after p + irradiation) used in the experiments.
One Rb:PPKTP sample was irradiated with 10 MeV protons (Sample 1), while the other one by the highest energy, 60 MeV protons (Sample 2), according to the procedure described above. After 60 MeV irradiation, Sample 2 became radioactive. It was kept at the proton irradiation facility for two weeks, after which the radiation decreased to the background level, and the sample could be handled safely. Investigation of possible nuclear reactions involved in the activation was outside the scope of this investigation. From the fact that the most abundant element in KTP is oxygen, one can speculate that transmutation reactions involving oxygen are the most likely source of radioactivity. There are several possible candidates for such reactions, with half-life times within tens of minutes and the cross sections peaking at the proton energy above 10 MeV [39–41].
The optical transmission measurement of the reference and irradiated samples showed that the measured relative transmission changes after irradiation was within 1%, i.e., within the measurement uncertainty.
Unavoidable logistics constraints due to the shipping of and the radioactivity from Sample 2 caused a delay of about six weeks between pre- and post-irradiation optical measurements. The OPO setup was kept intact over time, but minor differences in the pump laser characteristics could be expected. The study is limited to the modifications of the materials that did not relax within the six weeks delay between optical measurements, such as short-lived color centers that could be periodically annealed at temperature (T > 80°C) or suppressed by operation at elevated temperature. The performance of the crystals in the OPO before and after irradiation is summarized in Table 1, where, efficiencies were measured at the pump energy of 2.6 mJ. Within the margin of error, there is essentially no change in the OPO thresholds before and after proton irradiation for any of the crystals.
Table 1. The measured OPO, threshold energy at the same position in the crystals cross-section, and conversion efficiency at maximum (2.6 mJ) pump, before and after proton irradiations at 0,10 and 60 MeV.
Maps of deff over the cross-section of the Rb:PPKTP crystals are shown in Fig. 4. Yellow regions correspond to an almost perfect domain structure and a deff exceeding 10 pm/V [42]. In the blue regions, the domain grating has imperfections resulting in a lower deff. The latter is most evident at the edges of the crystals, which were not patterned for poling.
Fig. 4. Maps of the effective nonlinear coefficient of the three Rb:PPKTP crystals before and after proton irradiation, the crystallographic z-axis is along the ordinate and y-axis along the abscissa. (LEFT) Reference sample without irradiation, (MIDDLE) 10 MeV proton irradiation – Sample 1 and (RIGHT) 60 MeV proton irradiation – Sample 2.
From the 2D nonlinearity measurements before and after irradiation, we produced difference maps $d_{eff}^{before}(y,z) - d_{eff}^{after}(y,z)$, shown in Fig. 5. Differences in the characterization results of the reference sample was used for estimating the potential systemic bias error and the measurement uncertainty. The difference map of the reference sample shows an average difference of 2.8% in the effective nonlinearity. This can be attributed to the systemic changes in the pump laser parameters between two measurement campaigns.
Fig. 5. The normalized spatial differences of deff in percentages before and after irradiation with a 55 Gy equivalent dose in Si by 0 (Reference), 10 (Sample 1), and 60 MeV (Sample 2) protons, from left to right, respectively.
The 2D difference maps show that none of the irradiated samples had abrupt spatial variation, which could be expected if protons had been stopped completely in the crystals and a spatial charge layer with high defect concentration had developed. Such defect layers produced by ∼200 keV He ions are used to fabricate thin films in LiNbO3. It is known that such ion radiation damage decreases nonlinearity which, in LiNbO3, is recovered by thermal annealing procedures [43,44].
The 10 MeV irradiated sample had higher, while the 60 MeV had an overall lower measured $deff$ on average. By averaging all the measurement points within the crystal aperture cross-section, we estimate that, the 10 MeV sample has an average change of +4.0%, and 60 MeV has an average change of −0.5%, both very close to the measurement uncertainty. The results show that the irradiation at the proton energies of 10 MeV and 60 MeV and equivalent doses in Si of up to 55 Gy does not lead to the structural changes manifesting in the degradation of nonlinear properties of Rb:PPKTP.
The absence of structural damage and degradation of the nonlinear properties could be expected from calculating the proton stopping range in KTP. The stopping range is the distance at which protons are expected to come to rest in the material and depends on the material density and initial proton energy. According to quantum electrodynamic treatment of the charged particle scattering, each scattering event is associated with proton energy loss due to photon emission. Quite generally, the leading term in the scattering cross section depends inversely on the particle energy [45]. The strongest interaction and thus damage to the crystal structure is expected when the proton energy becomes commensurate with the crystal ionization and bonding energies and the protons are stopped in the bulk of the crystal. The calculation results using the NIST PSTAR model [36] are displayed in Fig. 6. The calculation shows that at both initial proton energies, the expected proton propagation range exceeds the thickness of the crystals.
4. Conclusions
We have investigated proton irradiation effects on Rb:PPKTP structures designed for operation in the OPA energy boost stages in 2 µm GHG sensing LIDAR. The irradiation regime was chosen to be relevant for a 5-year mission in low-Earth orbit, considering the prevailing trapped proton spectrum and the effects of satellite shielding. The Rb:PPKTP crystal aperture thickness was 5 mm, the largest available for periodically poled structures in this material. Measurements of the linear transmission and nonlinear properties of the structures before and after irradiation show that any changes to the performance are within the measurement uncertainty for the proton energies of 10 MeV and 60 MeV and doses corresponding to 55 Gy equivalent in Si. Activation of Rb:PPKTP after irradiation with protons at 60 MeV due to the creation of short-lived isotopes might be of some concern, as a thin satellite shield does not efficiently screen protons at such energies. However, this is not a unique feature pertinent for Rb:PPKTP. We observed similar activation in optical components fabricated from SiO2 and SiN. To the best of our knowledge, this is the first proton irradiation test on periodically-poled Rb:KTP crystals. This work's findings align with the previously reported results in single domain KTP crystals [22]. The results in this work strengthen the case for the large aperture Rb:PPKTP to be the material of choice in high-energy OPAs operating in a typical LEO satellite environment.
Funding
Horizon 2020 Framework Programme (821868).
Acknowledgments
The authors acknowledge the continuous support and collaboration from InnoLas Laser GmbH.
Disclosures
The authors declare no conflicts 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.
References
1. B. Luo, Y. Y. Yin, G. H. Huang, and Y. F. Huang, “Uncertainty analysis for distribution of greenhouse gases concentration in atmosphere,” J. Env. Inform. 3(2), 89–94 (2004). [CrossRef]
2. M. Meinshausen, E. Vogel, A. Nauels, K. Lorbacher, N. Meinshausen, D. M. Etheridge, P. J. Fraser, S. A. Montzka, P. J. Rayner, C. M. Trudinger, P. B. Krummel, U. Beyerle, J. G. Canadell, J. S. Daniel, I. G. Enting, R. M. Law, C. R. Lunder, S. O’Doherty, R. G. Prinn, S. Reimann, M. Rubino, G. J. M. Velders, M. K. Vollmer, R. H. J. Wang, and R. Weiss, “Historical greenhouse gas concentrations for climate modelling (CMIP6),” Geosci. Model Dev. 10(5), 2057–2116 (2017). [CrossRef]
3. C. Wührer, C. Kühl, S. Lucarelli, and M. Bode, “MERLIN: overview of the design status of the lidar Instrument,” in International Conference on Space Optics — ICSO 2018, Proc. SPIE (2019), Vol. 11180, p. 1118028.
4. G. Ehret, P. Bousquet, C. Pierangelo, M. Alpers, B. Millet, J. B. Abshire, H. Bovensmann, J. P. Burrows, F. Chevallier, P. Ciais, C. Crevoisier, A. Fix, P. Flamant, C. Frankenberg, F. Gibert, B. Heim, M. Heimann, S. Houweling, H. W. Hubberten, P. Jöckel, K. Law, A. Löw, J. Marshall, A. Agusti-Panareda, S. Payan, C. Prigent, P. Rairoux, T. Sachs, M. Scholze, and M. Wirth, “MERLIN: A French-German space lidar mission dedicated to atmospheric methane,” Remote Sens. 9(10), 1052 (2017). [CrossRef]
5. J. Hamperl, J. F. Geus, K. M. Mølster, A. Zukauskas, J. B. Dherbecourt, V. Pasiskevicius, L. Nagy, O. Pitz, D. Fehrenbacher, H. Schaefer, D. Heinecke, M. Strotkamp, S. Rapp, P. Denk, N. Graf, M. Dalin, V. Lebat, R. Santagata, J. M. Melkonian, A. Godard, M. Raybaut, and C. Flamant, “High energy parametric laser source and frequency-comb-based wavelength reference for CO2 and water vapor dial in the 2 µm region: design and pre-development experimentations,” MDPI Atmosphere 12(3), 402 (2021). [CrossRef]
6. A. Godard, M. Raybaut, and M. Lefebvre, “Nested Cavity Optical Parametric Oscillators – A Tunable Frequency Synthesizer for Gas Sensing,” Encyclopedia of Analytical Chemistry, 1–35 (2017).
7. A. Zukauskas, N. Thilmann, V. Pasiskevicius, F. Laurell, and C. Canalias, “5 mm thick periodically poled Rb-doped KTP for high energy optical parametric frequency conversion,” Opt. Mater. Express 1(2), 201–206 (2011). [CrossRef]
8. R. S. Coetzee, X. Zheng, L. Fregnani, F. Laurell, and V. Pasiskevicius, “Narrowband, tunable, 2 µm optical parametric master-oscillator power amplifier with large-aperture periodically poled Rb:KTP,” Appl. Phys. B 124(6), 124 (2018). [CrossRef]
9. R. S. Coetzee, N. Thilmann, A. Zukauskas, C. Canalias, and V. Pasiskevicius, “Nanosecond laser induced damage thresholds in KTiOPO4 and Rb:KTiOPO4 at 1 µm and 2 µm,” Opt. Mater. Express 5(9), 2090–2095 (2015). [CrossRef]
10. R. Bedington, X. Bai, E. Truong-Cao, Y. C. Tan, K. Durak, A. V. Zafra, J. A. Grieve, D. K. L. Oi, and A. Ling, “Nanosatellite experiments to enable future space-based QKD missions,” EPJ Quantum Technol. 3(1), 12 (2016). [CrossRef]
11. D. K. L. Oi, A. Ling, G. Vallone, P. Villoresi, S. Greenland, E. Kerr, M. Macdonald, H. Weinfurter, H. Kuiper, E. Charbon, and R. Ursin, “CubeSat quantum communications mission,” EPJ Quantum Technol. 4(1), 6–20 (2017). [CrossRef]
12. Z. Tang, R. Chandrasekara, Y. C. Tan, C. Cheng, L. Sha, G. C. Hiang, D. K. L. Oi, and A. Ling, “Generation and analysis of correlated pairs of photons aboard a nanosatellite,” Phys. Rev. Appl. 5(5), 054022 (2016). [CrossRef]
13. C. Canalias and V. Pasiskevicius, “Mirrorless optical parametric oscillator,” Nat. Photonics 1(8), 459–462 (2007). [CrossRef]
14. R. S. Coetzee, A. Zukauskas, C. Canalias, and V. Pasiskevicius, “Low-threshold, mid-infrared backward-wave parametric oscillator with periodically poled Rb:KTP,” APL Photonics 3(7), 071302 (2018). [CrossRef]
15. H. Prieto-Alfonso, L. Del Peral, M. Casolino, K. Tsuno, T. Ebisuzaki, and M. D. Rodríguez Frías, “Radiation hardness assurance for the JEM-EUSO space mission,” Reliab Eng. Syst. Saf. 133, 137–145 (2015). [CrossRef]
16. E. R. Benton and E. V. Benton, “Space radiation dosimetry in low-Earth orbit and beyond,” Nucl. Instrum. Methods Phys. Res., Sect. B 184(1-2), 255–294 (2001). [CrossRef]
17. S. T. Lai, K. Cahoy, W. Lohmeyer, A. Carlton, R. Aniceto, and J. Minow, “Deep dielectric charging and spacecraft anomalies,” in Extreme Events in Geospace: Origins, Predictability, and Consequences (2018), pp. 419–432.
18. R. S. Coetzee, S. Duzellier, J. B. Dherbecourt, A. Zukauskas, M. Raybaut, and V. Pasiskevicius, “Gamma irradiation-induced absorption in single-domain and periodically-poled KTiOPO4 and Rb:KTiOPO4,” Opt. Mater. Express 7(11), 4138 (2017). [CrossRef]
19. S. Tjornhammar, V. Maestroni, A. Zukauskas, T. K. Uždavinys, C. Canalias, F. Laurell, and V. Pasiskevicius, “Infrared absorption in KTP isomorphs induced with blue picosecond pulses,” Opt. Mater. Express 5(12), 2951 (2015). [CrossRef]
20. “The response of materials and devices to radiation - overall survey,” in Radiation Design Handbook, ESA PSS-01-609 Issue 1 (European Space Agency, 1993).
21. A. Ciapponi, W. Riede, G. Tzeremes, H. Schröder, and P. Mahnke, “Non-linear optical frequency conversion crystals for space applications,” Proc. SPIE 7912, 791205 (2011). [CrossRef]
22. U. Roth, M. Tröbs, T. Graf, J. E. Balmer, and H. P. Weber, “Proton and gamma radiation tests on nonlinear crystals,” Appl. Opt. 41(3), 464–469 (2002). [CrossRef]
23. C. Granja and S. Polansky, “Mapping the space radiation environment in LEO orbit by the SATRAM Timepix payload on board the Proba-V satellite,” AIP Conf Proc1753, (2016). [CrossRef]
24. R. Campana, M. Orlandini, E. Del Monte, M. Feroci, and F. Frontera, “The radiation environment in a low earth orbit:the case of BeppoSAX,” Exp. Astron. 37(3), 599–613 (2014). [CrossRef]
25. ISO 15856:2010, “International Standard. Space systems - Space environment -Simulation guidelines for radiation exposure for non-metallic materials,” ISO (2010).
26. ESA, “The Space environment Information System, Spenvis,” https://www.spenvis.oma.be/.
27. G. P. Ginet, T. P. O’Brien, S. L. Huston, W. R. Johnston, T. B. Guild, R. Friedel, C. D. Lindstrom, C. J. Roth, P. Whelan, R. A. Quinn, D. Madden, S. Morley, and Y.-J. Su, “AE9, AP9 and SPM: New Models for Specifying the Trapped Energetic Particle and Space Plasma Environment,” in The Van Allen Probes Mission., J. L. Fox and N. Burch, eds., (Springer, 2013), pp. 579–615.
28. D. Sinclair and J. Dyer, “Radiation Effects and COTS Parts in SmallSats,” 27th Annual AIAA/USU Conference on Small Satellites1–12 (2013).
29. C. Poivey, “Radiation hardness assurance for space systems,” in IEEE NSREC Short Course, Phoenix, AZ (2002), pp. 1–58.
30. S. Buchner, P. Marshall, S. Kniffin, and K. LaBel, “Proton Test Guideline Development–Lessons Learned,” in NASA Electronic Parts and Packaging Program (2002), pp. 1–69.
31. S. A. Graves, P. A. Ellison, T. E. Barnhart, H. F. Valdovinos, E. R. Birnbaum, F. M. Nortier, R. J. Nickles, and J. W. Engle, “Nuclear excitation functions of proton-induced reactions (Ep = 35–90 MeV) from Fe, Cu, and Al,” Nucl. Instrum. Methods Phys. Res., Sect. B 386, 44–53 (2016). [CrossRef]
32. H. Bethe, “Zur Theorie des Durchgangs schneller Korpuskularstrahlen durch Materie,” Ann. Phys. 397(3), 325–400 (1930). [CrossRef]
33. E. Bär, P. Andreo, A. Lalonde, G. Royle, and H. Bouchard, “Optimized I-values for use with the Bragg additivity rule and their impact on proton stopping power and range uncertainty,” Phys. Med. Biol. 63(16), 165007 (2018). [CrossRef]
34. K. S. Sharada, “Proton stopping powers in some low-Z elements,” Radiat. Res. 136(3), 335–340 (1993). [CrossRef]
35. D. I. Thwaites, “Bragg’s rule of stopping power additivity : a compilation and summary of results,” Radiat. Res. 95(3), 495–518 (1983). [CrossRef]
36. NIST, “PSTAR: Stopping power and range tables for protons,” https://physics.nist.gov/PhysRefData/Star/Text/PSTAR.html.
37. F. Gibert, J. Pellegrino, D. Edouart, C. Cénac, L. Lombard, J. Le Gouët, T. Nuns, A. Cosentino, P. Spano, and G. Di Nepi, “2-µm double-pulse single-frequency Tm:fiber laser pumped Ho:YLF laser for a space-borne CO2 lidar,” Appl. Opt. 57(36), 10370 (2018). [CrossRef]
38. S. J. Brosnan and R. L. Byer, “Optical parametric oscillator threshold and linewidth studies,” IEEE J. Quantum Electron. 15(6), 415–431 (1979). [CrossRef]
39. S. C. Curran and J. E. Strothers, “Bombardment of nitrogen and oxygen with protons,” Nature 145(3667), 224 (1940). [CrossRef]
40. T. Masuda, J. Kataoka, M. Arimoto, M. Takabe, T. Nishio, K. Matsushita, T. Miyake, S. Yamamoto, T. Inaniwa, and T. Toshito, “Measurement of nuclear reaction cross sections by using Cherenkov radiation toward high-precision proton therapy,” Sci. Rep. 8(1), 2570 (2018). [CrossRef]
41. F. Horst, W. Adi, G. Aricò, K. T. Brinkmann, M. Durante, C. A. Reidel, M. Rovituso, U. Weber, H. G. Zaunick, K. Zink, and C. Schuy, “Measurement of PET isotope production cross sections for protons and carbon ions on carbon and oxygen targets for applications in particle therapy range verification,” Phys. Med. Biol. 64(20), 205012 (2019). [CrossRef]
42. M. V. Pack, D. J. Armstrong, and A. V. Smith, “Measurement of the χ2 tensors of KTiOPO4, KTiOAsO4, RbTiOPO4, and RbTiOAsO4 crystals,” Appl. Opt. 43(16), 3319–3323 (2004). [CrossRef]
43. G. Poberaj, H. Hu, W. Sohler, and P. Gümter, “Lithium niobate on insulator (LNOI) for micro-photonic devices,” Laser Photonics Rev. 6(4), 488–503 (2012). [CrossRef]
44. P. Bindner, A. Boudrioua, J. C. Loulergue, and P. Moretti, “Formation of planar optical waveguides in potassium titanyl phosphate by double implantation of protons,” Appl. Phys. Lett. 79(16), 2558–2560 (2001). [CrossRef]
45. D. R. Yennie, S. C. Frautschi, and H. Suura, “The infrared divergence phenomena and high-energy processes,” Ann. Phys. 13(3), 379–452 (1961). [CrossRef]
