# Laser Technology in Photonic Applications for Space
## 3 Lasers in Space
### Science
#### 3.1.1 Remote Sensing (LIDAR)
The first topographic mapping of the Moon from orbit was performed by Apollo 15 in 1970, which was then extended by the Apollo 16 and Apollo 17 missions. The lasers were flash-lamp pumped based and mechanically Q-switched with a ruby laser emitting at 694.23 nm with a pulse energy of 200 nJ and a pulse width of 10 ns [35]. In 1994, the Clementine mission was launched, which mapped the surface of the Moon over a period of more than two months. It carried on board a compact, lightweight, diode-pumped Nd:Cr:YAG laser, emitting pulses of 180 m) energy and 10 ns width at 1064 nm. The Q-switching was performed by a Lithium Niobate (LiNbO\({}_{3}\)) crystal-based Pockels cell [47]. SELENE, also known as Kaguya, was a Japanese mission launched in 2007 that orbited the Moon for more than one and a half years and surveyed it with LIDAR technology using an Nd:YAG laser with 100 mJ output power at 1064 nm, a pulse width of 15 ns and a repetition rate of 1 Hz. The Q-switch was also performed actively by a LiNbO\({}_{3}\)-based Pockels cell [48]. China also created a lunar exploration program called Chang'E. The first mission was launched in 2007 and the lunar surface was mapped between November 2007 and July 2008. The laser specifications were similar to those of previous missions, with an output wavelength of 1064 nm emitted from a diode-pumped Nd:YAG crystal actively Q-switched with a potassium dideuterium phosphate (KD\({}^{\text{*}}\)P) crystal. The energy emitted was 150 mJ per pulse and a pulse width of less than 7 ns at repetition rate of 1 Hz [49]. A similar laser was used for the Chang'E-2 mission launched in 2010, but with a repetition rate of 5 Hz. The resolution of the measurements was increased to achieve a 5 m vertical accuracy [50]. In 2008, India launched its first lunar probe called Chandrayaan, equiped with the Lunar Laser Ranging Instrument (LLRI) that mapped the surface topography using a Q-switched Nd:YAG laser at 1064 nm with a pulse energy of 100 mJ and a pulse width of 15 ns. The active Q-switching was also performed by an LiNbO\({}_{3}\) crystal [30]. The NASA Lunar Orbiter Laser Altimeter (LOLA) was also launched in 2008, one of its objective being the validation of technologies for following missions to the Moon. It uses a DPSSL with an Nd:Cr:YAG slab with passive Q-switch and a cross-Porro resonator configuration working at 1064 nm, 28 Hz repetition rate and about 3 mJ at 5 ns for the both mounted redundant lasers [51; 52]. The NASA DPSSL for MOLA was launched in 1996 with the objective of studying the Martian topography. The mission used a diode-pumped, Nd:Cr:YAG zigzag slab, cross-Porro, electro-optically Q-switched laser transmitter. The laser design parameters were 40 mJ energy with pulse width of 10 ns and repetition rate of 10 Hz, although the experimental data was closer to 45 mJ with pulses of 8 ns width [53]. In 2008, the PHOENIX lander, equipped with a LIDAR system, reached Mars. The dual wavelength Nd:YAG laser it carried was capable of delivering pulses with energies of 30 mJ at 1064 nm and 40 mJ at 532 nm after frequency-doubling in a KTP crystal with a pulse width of 15 ns at a repetition rate of 100 Hz provided by a saturable observer. The apparatus was used to study the Martian atmospheric dust, clouds, and precipitations, such as ice, fog, and snow [54]. The Mercury Laser Altimeter (MLA) on board of the NASA mission MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) launched in 2004 is a passive Q-switched LIDAR laser operating with 5 ns and 20 mJ laser pulses at a 8 Hz rate used to gather topographic information of the planet. In this case, the configuration used a similar zigzag slab design, although in other aspects, its design had a direct image from the GLAS laser passively Q-switched DPSSL [52; 55].