# Laser Technology in Photonic Applications for Space
## 5 Difficulties, Drawbacks--But Also Final Advantages  
Laser devices, photonic devices, and more generally any device launched in space will experience harsh environments during operation, as explained in Section 4. The principal challenge here is to adapt novel sophisticated engineered setups that operate satisfactorily on stable optical tables in controlled laboratory environments into operating devices able to withstand extreme conditions that will eventually misalign or damage the optical components and cause final device failure.  
In the specific case of laser diodes, the indium used to package the laser chip could represent a risk in case of extreme temperatures ranges due to the indium creep behaviour that can lead to fatal device failure [135]. Moreover, high vacuum regimes can even cause changes in the chemical and physical properties of components due to dehydration [137]. Another common issue for the laser crystals and fibers is the photodarkening effect produced in optical components due to radiation absorption. Many studies have been performed on the effects of several types of radiation on various laser materials with different doping ratios [138; 139], which photonic space engineers should check in order to select the best candidates for their assemblies. This issue can be easily solved by improving the components shielding, however, the increased thickness caused by the extra layers of material protecting the components increases the weight of the integrated device, and frequently its size and cost. For that reason, the components must be carefully selected for optimum match with the mission radiation budgets to ensure that the laser output maintains the required specifications over the long operational period of the mission without incurring in unnecessary cost caused by extra shielding.  
Standard assembly techniques used for laser components are also not generally space compatible. For instance, organic epoxies, which are commonly used, cause out-gassing issues, creating laser  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Frequency (Hz)** & **Level** \\ \hline
20 & 0.052 g\({}^{2}\)/Hz \\
20–50 & +6 dB/octave \\
50–800 & 0.32 g\({}^{2}\)/Hz \\
800–2000 & \(-6\) dB/octave \\
2000 & 0.052 g\({}^{2}\)/Hz \\ Overall & 20.0 grams \\ \hline \hline \end{tabular}
\end{table}
Table 1: Random vibrational mission limits required for components lifetime to be performed several minutes per axis [19; 131].  
induced contamination (LIC) and further laser induced damage (LID) [140]. Packaging issues can be solved by using new packaging technologies. Replacing adhesives by techniques, such as low-stress soldering techniques [141], will contribute towards providing more robust DPSSL devices with higher thermal range, higher mechanical strength, lower out-gassing, and improved bonded-materials resistant to radiation.  
Some of the advantages offered by new photonic devices over those previously used that make up for the challenge that the environmental tests suppose have been already mentioned in this article [5]:  
* almost limitless bandwidth for lasercom devices,
* immunity to electromagnetic waves,
* reliability,
* efficient and low power consumption,
* small form factor,
* low weight.  
The final decision to select previously used space-qualified technologies, new photonic qualified devices with high technological readiness level, or completely new and in-development setups will be based on advantages and real needs of the selected option, mission budgets, and possible risks produced by device failure when subjected to space environments. Both reliability and cost factors are important requirements that often greatly affect the design choice, the former also affecting the efficiency trade that needs to be made in terms of de-rating for lifetime.