Development of a Programmable UV Laser Source for the Dragonfly Mass Spectrometer (DraMS)

Abstract

NASA's Dragonfly mission will sample surface materials from multiple sites on Saturn's largest moon, Titan, in exploration of its potential for prebiotic chemistry. We are developing and delivering a compact pulsed UV laser transmitter, developed in-house at NASA's Goddard Space Flight Center, capable of directing programmable 266 nm pulse energies to a small sample of surface material for Laser Desorption Mass Spectrometry (LDMS) performed by the on-board Dragonfly Mass Spectrometer (DraMS). The mail goal for this effort was to develop a flight-capable, two-part design, employing a remotely located fiber coupled pumping source, and a UV transmitter unit that can operate in short bursts with minimal change in laser pulse characteristics such as beam quality, pointing, energy, and pulse width. The DraMS UV source will require a 7+ year transit to the Saturn system; where upon deployment on Titan's surface, must demonstrate a combination of survivability, reliability, operational capability, and performance yet developed in a flightqualified solid-state laser transmitter. Once Dragonfly is safely operational, the Titan Hydrocarbon Analysis Nanosecond Optical Source (THANOS) UV laser will perform for 3+ years in Titan's extreme surface and atmospheric conditions in several locations.

Performance of the dragonfly mass spectrometer (DraMS) programmable UV laser source engineering test unit (ETU)

“…The Laser Optics Box (LOBleft in Figure 2) is described in detail in previous publications, but as a brief overview, it consists of an end-pumped Nd:YAG rod, in a compact passively Q-Switched (QS) linear oscillator cavity producing ~ 2 mJ 1064 nm pulses at < 2 ns. 6 The infrared laser pulses are then frequency quadrupled to a 266 nm output and directed by the BSU to the Titan surface sample of study. Included in the optics chain is a Rubidium Titanyle Potassium (RTP) electro-optic crystal pair and a polarizing beam splitting (PBS) cube.…”

Technology development of a solid state 266 nm laser for NASA’s Dragonfly mission

“…The laser optics box (LOB) is comprised of a Nd:YAG-based Q-Switched (QS) laser cavity, a pulse energy electro-optic "throttle", a non-linear optics chain, and an external beam steering unit (BSU) mounted to the LOB's exterior. 7 The fiber coupled 885 nm light is collimated and focused into the main oscillator consisting of a 22 mm Nd:YAG crystal rod, a passive CR4+:YAG QS, a polarizing beam splitter, a risley pair and a 35% reflective concave output coupler. The oscillator produces 2 mJ pulses at 1064 nm, ~1.7 ns in width.…”

Damage threshold testing of UV optics under a Titan environment for NASA’s Dragonfly Mission

“…Once the desired UV pulse energy is produced, it is sent out of the pressurized laser enclosure through a sealed window in its base, and into the Beam Steering Unit (BSU), as shown in Figure 2 To save mass, complexity, and cost, the laser housing-to-sample optical path will be non-hermetically enclosed, and thus exposed to the Titan atmosphere and its chemical constituents. 5 Therefore, a Beam Steering Unit (BSU) has been developed that mount directly to the laser's output window flange and directs the UV pulses to the sample with high precision. The BSU, described in Figure 2, consists of two flat highly reflective (HR) UV mirrors, two slightly wedged rotating UV steering prisms, or risleys, and one custom focusing lens.…”

“…Prior to our engineering test unit development, a breadboard system had been constructed, optimized, and used for life testing, component characterization, and optical damage testing experiments. 5 This system proved out to be a suitable analog to simulate operation and performance of any optics at risk outside the sealed laser vessel and exposed to the Titan atmosphere. This breadboard laser system was used as the UV source for the entirety of the testing described in this paper and was an ideal candidate to match the laser characteristics that is seen in the engineering test unit (ETU) version of the THANOS system.…”

“…3,4 The pulsed UV laser, developed by NASA GSFC's Lasers and Electro-Optics Branch, is a sealed solid state transmitter, designed to meet DraMS' science requirements. 5 These Figure 1. The Dragonfly Mass Spectrometer is housed in the "attic" of the Dragonfly rotorcraft, which is split into a warm and cold zone; or a thermally controlled zone and one exposed to Titan's temperatures, respectively.…”