For many years now most major astronomical observatories have been using adaptive optics (AO) with the aid of optical or ultra-violet lasers to generate artificial guide stars. While the majority of laser-based AO systems in use have been used to feed infrared science cameras, there have always been scientific reasons to use these systems with optical cameras as well. One challenge in the optical region is that these lasers themselves contaminate the sky at their respective wavelengths. This contamination is an issue not only for the telescope itself but also for any other optical telescope looking at or near the laser beam. Up until recently it was thought that these lasers only contaminated the sky at their respective wavelengths. However, recent studies at the VLT have shown that there are additional, albeit much weaker, sources of contamination caused by inelastic Raman scattering of the laser light, also in the optical region. These observations were made with the VLTs MUSE spectrograph looking at the ESO 4LGSF which uses 4 Toptica Sodium Star 20/2 lasers to make a variety of different laser guide star constellations both on axis and off axis from the science camera, the total output power of the 4 lasers is on the order of 88W. At the Gemini South observatory at Cerro Pachón we propagated either a single 45W Lockheed Martin Coherent Technologies (LMCT) pulsed laser, or a single Toptica Sodium Star 20/2 continuous wave laser. In each case the beam was split into 5 beams of equal intensity and center-launched so as to always be on axis with the science camera. We used the GMOS-S spectrograph to take on axis spectra of the laser beams, looking for the same Raman lines detected at the VLT. For both lasers, we were able to detect the Raman emission lines. In this paper we will present the results from our GMOS-S spectroscopy detailing the wavelength and intensities of the Raman emission for each laser.
Sodium guide star technologies for Adaptive Optics (AO) have been around for over 20 years. During this time, the technologies for the lasers used to excite the mesospheric sodium have been in constant development, with the goals being not only to excite as much sodium as possible, but to do so efficiently, while producing a round guide star, and while offering a reliable facility. The first lasers in use were dye lasers with a liquid gain medium, while these lasers were able to produce sodium guide stars, the liquid dye used was toxic and flammable. The second generation of guide star lasers used sum-frequency-mixed solid-state lasers. These lasers provided excellent return but were notoriously difficult to calibrate and maintain, requiring a full-time laser engineer on staff. The current third generation of sodium guide star lasers use Raman fiber amplification to generate a laser that is very efficient at exciting sodium with a good spot profile and offer a high degree of reliability. The Gemini South observatory for the last few years has been in the process of obtaining one of these third-generation lasers, a Toptica Sodium Star 20/2 while maintaining its second-generation Lockheed Martin Coherent Technologies (LMCT) 50W CW Mode-locked laser. In October of 2017 successful on-sky commissioning of the Toptica laser was executed while the LMCT laser was still active and in operations. During the course of the commissioning run both lasers were used on sky in close in time in possible. We present a comparative study of the performance of each laser.
Adaptive Optics (AO) systems aim at detecting and correcting for optical distortions induced by atmospheric turbulences. The Gemini Multi Conjugated AO System GeMS is operational and regularly used for science observations since 2013 delivering close to diffraction limit resolution over a large field of view. GeMS entered this year into a new era. The laser system has been upgraded from the old 50W Lockheed Martin Coherent Technologies (LMCT) pulsed laser to the Toptica 20/2W CW SodiumStar laser. The laser has been successfully commissioned and is now used regularly in operation. In this paper we first review the performance obtained with the instrument. I will go then into the details of the commissioning of the Toptica laser and show the improvements obtained in term of acquisition, stability, reliability and performance.
Lockheed Martin Coherent Technologies has developed 20 W and 50 W commercial solid-state sodium beacon Guidestar Laser Systems (GLS) for the Keck I and Gemini South telescopes, respectively. This work represents a critical step toward addressing the need of the astronomical adaptive optics (AO) community, including multi-conjugate AO and AO tomography for future extremely large telescopes. This paper describes the status of GLS for the Keck I and Gemini South telescopes. The design and experimental results of the laser oscillators, amplifiers and sum-frequency generator will be discussed.
Lockheed Martin Coherent Technologies (LMCT) is developing 20 W and 50 W commercial solid-state sodium beacon Guidestar Laser Systems (GLS) for the Keck I and Gemini South telescopes, respectively. This work represents a critical step toward addressing the need of the astronomical adaptive optics (AO) community for a standardized, robust, turn-key, commercial GLS that can be configured for different observatory facilities and for different AO formats - including multi-conjugate AO (MCAO) and future extremely large telescopes. These modular systems build on the proven laser technologies, user-friendly interface, and low maintenance design that were developed for the successful 12 W GLS delivered by LMCT to the Gemini North telescope in February 2005. This paper describes the GLS requirements for the Keck I and Gemini South telescopes, the design of the laser oscillators, amplifiers, sum-frequency generator, and diagnostics; the functionality of the automated remote laser control system; size, weight, power, and performance data; and the current status of the programs.
Lockheed Martin Coherent Technologies (LMCT) reports on the development of a compact, scalable versatile optical waveform sodium guidestar laser system (GLS) suitable for Adaptive Optics (AO) systems on Extremely Large Telescopes (ELT's) and smaller telescopes. We have successfully completed phase 1 of the three-phase, 4½ year, NSF funded, National Optical Astronomy Observatory (NOAO) sponsored program. The GLS can be optimized for efficient sodium layer interaction for each telescope / AO system with mitigation of parasitic effects such as Rayleigh or cirrus cloud scatter of adjacent beacon light in multi-conjugate adaptive optics (MCAO) and spot elongation in the sodium layer from off-axis light launch in an ELT. The proposed solid-state laser architecture incorporates patent-pending self-imaging waveguide technology and is based on a set of requirements that was determined after extensive discussions with the astronomy adaptive optics community. This paper presents data on single beacon, Rayleigh compensating, and elongation compensating waveforms that were demonstrated through all stages of the architecture, as well as demonstrated and anticipated 589 nm power levels for each waveform. The design of the master oscillator power amplifier (MOPA) architecture, modulation methodology, power amplification, and sum-frequency generation stages is also described. System attributes, including size, weight, and power will also be discussed.
We report on the first successful installation of a commercial solid-state sodium guidestar laser system (GLS). The GLS developed at LMCT was delivered to Gemini North Observatory in February of 2005. The laser is a single beacon system that implements a novel laser architecture and represents a critical step towards addressing the need of the astronomy and military adaptive optics (AO) communities for a robust turn-key commercial GLS. The laser was installed on the center section of the 8 m Gemini North telescope, with the output beam relayed to a laser launch telescope located behind the 1 m diameter secondary mirror. The laser went through a three week performance evaluation between November and December 2005 wherein it consistently generated 12 W average power with measured M2 < 1.1 while locked to the D2 line at +/- 100 MHz. The system was required to perform during a 12-hour test period during three runs of 4-6 consecutive nights each. The laser architecture is based on continuous wave (CW) mode-locked solid-state lasers. The mode-locked format enables more efficient SFG conversion, and dispenses with complex resonant intensity enhancement systems and injection-locking electronics. The linearly-polarized, near-diffraction-limited, modelocked 1319 nm and 1064 nm pulses are generated in separate dual-head diode-pumped resonators. The two IR pulses are input into a single-stage, 30 mm PPSLT sum-frequency generation (SFG) crystal provided by Physical Science, Inc. Visible (589 nm) power of >16 W have been generated, representing a conversion efficiency of 40%.
Coherent Technologies, Inc. (CTI) is developing the first commercial solid-state sodium beacon laser guidestar (LGS): a critical step towards addressing the need of the astronomy adaptive optics (AO) community for a robust turn-key commercial LGS that can be upgraded for different observatory facilities and for different AO formats - including multi-conjugate AO (MCAO) and future extra-large telescopes. The LGS that is currently being developed will be a 14 W single beacon system to be installed on the center section of the Gemini North telescope in Fall 2004. This paper describes the Gemini North LGS requirements, the design of the laser with design trades against other LGS architectures; the functionality of the automated remote laser control system; latest size, weight, power, and performance data; and the current status of the program.
Broadly tunable infrared laser sources are of interest for a variety of applications including differential absorption lidar, differential scattering lidar, multi-spectral detection and imaging, hard target identification and discrimination, optical communications in poor visibility conditions, and spectroscopy. For chemical sensing applications, sources are particularly sought in the mid-wave infrared (MWIR) and long-wave infrared (LWIR) spectral regions. A variety of laser and nonlinear optical devices have been demonstrated that access these wavelengths. In particular, CTI is developing novel, tunable, narrow linewidth transmitters for coherent and direct detection lidar measurement applications. An example is a multi-watt Cr:ZnSe laser that is tunable over the 2.1 to 2.8 micrometers wavelength region. This laser has been used to pump-tune optical parametric oscillators (OPOs) that are broadly tunable across the MWIR and LWIR. We are also developing tunable Yb lasers that can be used to pump OPOs that emit signal beams in the eyesafe 1.55 micrometers region while generating idler beams that access the 3 to 4 micrometers MWIR band. This paper describes these sources.
The ultrafast laser industry has been built upon the scientific research market with the assumption that certain factors such as electrical power, cooling, and vibration isolation can be taken for granted. As ultrafast lasers stand ready to break into the industrial laser market, these and many other assumptions must be re-examined. This paper presents a discussion of the many non-trivial engineering issues that must be addressed in order to bring a highly sophisticated laser system into the harsh industrial environment. These practical considerations include performance, reliability, and cost of ownership. The foundation of the discussion is based upon lessons drawn from successful existing industrial laser systems such as CO2 and Nd:YAG. Relevant results from this study will then be applied to the particular case of ultrafast lasers with the goal of examining how current scientific lasers compare with industrial requirements and highlighting some technologies which can help bridge this gap.
We present a characterization of the significant noise mechanisms in a microchannel image intensifier and CCD image recording system intended for applications in ultrafast imaging systems used at LLNL for nuclear science. The system under study consists of a generation two image intensifier a relay lens and a cooled CCD imaging array of 640 by 1024 pixels. Fixed pattern noise is significantly reduced by flat fielding techniques. The remaining major noise mechanisms are the intensifier shot noise and a noise factor that characterizes the non-idealness of the system. Results are given for the intensifier noise factor'' s functional dependence on input irradiance levels gain settings and accelerating voltages.