SEARCH · Engineering Papers
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Solid-state dye lasers, pumped by a doubled Nd:YAG laser, were evaluated as a function of concentration, output coupler reflectivity and oscillator dimensions. A slope efficiency of up to 62 pct was achieved. A maximum irradiance of 59 MW/sq cm to the dye laser cavity was achieved.
The applications of Q-switched lasers are well known, for example, laser radar, laser remote sensing, satellite orbit determination, Moon orbit and 'moon quake' determination, satellite laser communication, and many nonlinear optics applications. Most of the applications require additional properties of the Q-switched lasers, such as single-axial and/or single-transverse mode, high repetition rate, stable pulse shape and pulse width, or ultra compact and rugged oscillators. Furthermore, space based and airborne lasers for lidar and laser communication applications require efficient, compact, lightweight, long-lived, and stable-pulsed laser sources. Diode-pumped solid-state lasers (DPSSL) have recently shown the potential for satisfying all of these requirements. We will report on the operating characteristics of a diode-pumped, monolithic, self-Q-switched Cr,Nd:YAG laser where the chromium ions act as a saturable absorber for the laser emission at 1064 nm. The pulse duration is 3.5 ns and the output is highly polarized with an extinction ratio of 700:1. It is further shown that the output is single-longitudinal-mode with transform-limited spectral line width without pulse-to-pulse mode competition. Consequently, the pulse-to-pulse intensity fluctuation is less than the instrument resolution of 0.25 percent. This self-stabilization mechanism is because the lasing mode bleaches the distributed absorber and establishes a gain-loss grating similar to that used in the distributed feedback semiconductor lasers. A repetition rate above 5 KHz has also been demonstrated. For higher power, this laser can be used for injection seeding an amplifier (or amplifier chain) or injection locking of a power oscillator pumped by diode lasers. We will discuss some research directions on the master oscillator for higher output energy per pulse as well as how to scale the output power of the diode-pumped amplifier(s) to multi-kilowatt average power.
The stimulated Raman scattering (SRS) and four-wave mixing (FWM) processes are studied in detail in CH4 gas pumped by the third-harmonic of Nd:YAG laser at 355 nm. The conversion efficiency and average output energy are measured for the various Stokes and anti-Stokes lines at different experimental conditions. The threshold input energy at various CH4 pressures is calculated for the unguided and capillary waveguide Raman cells. The calculated values for the capillary case are compared with the measured values at different CH4 pressures and the two results are in good agreement.
A Q-switched Nd:YLF laser (model 110-02) and a Nd:YAG ring laser (model 120-04) from Lightwave Electronics were subjected to thermal and vibration tests similar to what can be expected during launch and flight on a spacecraft. Even though these lasers were not designed for space flight, environmental tests were performed to identify major design weaknesses. Laser performance (output power, energy, pulsewidth, lasing threshold etc.) were measured prior to and after thermal vibration tests. Average output power of the Q-switched laser degraded 15-20 percent after thermal tests and an additional 20-25 percent after vibration tests. Post diagnostic tests revealed that degradation of the Q-switched laser was due to misalignment of pump focusing optics and the laser cavity.
Flash-lamp-pumped normal-mode and Q-switched 2.1-micron laser operations of Ho:Tm:Cr:YAG crystals have been evaluated under a wide variety of experimental conditions in order to determine an optimum lasing condition and to characterize the laser outputs. Q-switched laser-output energies equal to, or in some cases exceeding the normal-mode laser energies, were obtained in the form of a strong single spike through an optimization of the opening time of a lithium niobate Q switch. The increase of the normal-mode laser slope efficiency was observed with the increase of the Tm concentration from 2.5 to 4.5 at. pct at operating temperatures from 120 K to near room temperature. Laser transitions were observed only at 2.098 and 2.091 microns under various conditions. The 2.091-micron laser transition appeared to be dominant at high-temperature operations with low-reflective-output couplers.
Multiple descriptions of the alumina-YAG eutectic crystallography appear in the ceramic literature. The orientation between two phases in a eutectic system has direct impact on residual stress, morphology, microstructural stability, and high temperature mechanical properties. A study to demonstrate that the different crystallographic relationships can be correlated with different growth constraints was undertaken. Fibers produced by Laser-Heated Float Zone (LHFZ) and Edge-defined Film-fed Growth (EFG) were examined. A map of the orientation relationship between Al2O3 and Y3Al5O12 and their relationship to the fiber growth axis as a function of pull rate are presented. Regions in which a single orientation predominates are identified.
Room temperature operation of flashlamp pumped Nd:YAG at 0.946 micrometers was achieved with a laser rod having undoped ends. Performance was characterized and compared with 1.064 micrometer operation and other quasi four level lasers.
A compact, passively Q-switched Nd:YAG laser has been developed for the Mercury Laser Altimeter (MLA) instrument which is an instrument on the MESSENGER mission to the planet Mercury. The laser achieves 5.4 percent efficiency with a near diffraction limited beam. It has passed all space flight environmental tests at system, instrument, and satellite integration. The laser design draws on a heritage of previous laser altimetry missions, specifically ISESAT and Mars Global Surveyor; but incorporates thermal management features unique to the requirements of an orbit of the planet Mercury.
Room temperature Ho:YAG and Ho:LuAG lasers pumped by a Tm:YLF laser demonstrated a 3.4 mJ threshold and 0.41 slope efficiency, incident optical to laser output energy. Results for numerous rod lengths, Ho concentrations, and output mirror reflectivities are presented.
In this paper, recent progress made in the design and development of an all-solid-state, single longitudinal mode, conductively cooled Nd:YAG laser operating at 1064 nm wavelength for UV lidar for ozone sensing applications is presented. Currently, this pump laser provides an output pulse energy of greater than 1.1 J/pulse at 50 Hz PRF and a pulsewidth of 22 ns. The spatial profile of the output beam is a rectangular super Gaussian. Electrical-to-optical system efficiency of greater than 7% and a minimum M(sup 2) value of less than 2 have been achieved.
A diode pumped, Nd:YAG laser producing 100 mJ Q-switched pulses and employing a dual-pump head scheme in an unstable resonator configuration is described. Each head contains a side pumped zig-zag slab and four 6-bar QCW 808 nm diodes arrays which are de-rated 23%. Denoting 'z' as the lasing axis, the pump directions were along the x-axis in one head and the y-axis in the other, producing a circularized thermal lens, more typical in laser rod-based cavities. The dual head design's effective thermal lens is now corrected with a proper HR mirror curvature selection. This laser has demonstrated over 100 mJ output with high optical efficiency (24%), good TEM(sub 00) beam quality, and high pointing stability.
Up conversion significantly affects Er:YAG lasers. Measurements performed here for low Er concentration are significantly different than reported high Er concentration. The results obtained here are used to predict laser performance and are compared with experimental results.
This paper describes the fabrication of a rugged, laser-welded package for a 200mW, monolithic diode-pumped solid state Nd:YAG laser operating at 1319nm.
AgY(WO4)2 crystallizes in the monoclinic P2/c space group. The structure is three-dimensional. Y3+ is bonded to six O2- atoms to form distorted YO6 octahedra that share corners with eight equivalent WO6 octahedra and edges with two equivalent AgO6 octahedra. The corner-sharing octahedra tilt angles range from 36–60°. There are a spread of Y–O bond distances ranging from 2.27–2.37 Å. W6+ is bonded to six O2- atoms to form distorted WO6 octahedra that share corners with four equivalent YO6 octahedra, corners with four equivalent AgO6 octahedra, and edges with two equivalent WO6 octahedra. The corner-sharing octahedra tilt angles range from 36–61°. There are a spread of W–O bond distances ranging from 1.83–2.18 Å. Ag1+ is bonded to six O2- atoms to form distorted AgO6 octahedra that share corners with eight equivalent WO6 octahedra and edges with two equivalent YO6 octahedra. The corner-sharing octahedra tilt angles range from 43–61°. There are a spread of Ag–O bond distances ranging from 2.34–2.59 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to one Y3+, one W6+, and one Ag1+ atom. In the second O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent W6+ and one Ag1+ atom. In the third O2- site, O2- is bonded in a 3-coordinate geometry to one Y3+, one W6+, and one Ag1+ atom. In the fourth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Y3+ and two equivalent W6+ atoms.
AgY(IO3)4 crystallizes in the monoclinic Cc space group. The structure is two-dimensional and consists of two AgY(IO3)4 sheets oriented in the (1, 0, 0) direction. there are two inequivalent Y3+ sites. In the first Y3+ site, Y3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Y–O bond distances ranging from 2.31–2.45 Å. In the second Y3+ site, Y3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Y–O bond distances ranging from 2.32–2.52 Å. There are two inequivalent Ag1+ sites. In the first Ag1+ site, Ag1+ is bonded in a 8-coordinate geometry to seven O2- atoms. There are a spread of Ag–O bond distances ranging from 2.37–2.88 Å. In the second Ag1+ site, Ag1+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Ag–O bond distances ranging from 2.39–2.93 Å. There are twenty-four inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to one Y3+, one Ag1+, and one I5+ atom. The O–I bond length is 1.86 Å. In the second O2- site, O2- is bonded in a 1-coordinate geometry to one I5+ atom. The O–I bond length is 1.85 Å. In the third O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Y3+ and one I5+ atom. The O–I bond length is 1.84 Å. In the fourth O2- site, O2- is bonded in a 2-coordinate geometry to one Y3+ and one I5+ atom. The O–I bond length is 1.86 Å. In the fifth O2- site, O2- is bonded in a distorted single-bond geometry to one I5+ atom. The O–I bond length is 1.83 Å. In the sixth O2- site, O2- is bonded in a distorted single-bond geometry to one I5+ atom. The O–I bond length is 1.83 Å. In the seventh O2- site, O2- is bonded in a 2-coordinate geometry to one Y3+, one Ag1+, and one I5+ atom. The O–I bond length is 1.87 Å. In the eighth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Y3+, one Ag1+, and one I5+ atom. The O–I bond length is 1.84 Å. In the ninth O2- site, O2- is bonded in a 2-coordinate geometry to one Y3+, one Ag1+, and one I5+ atom. The O–I bond length is 1.83 Å. In the tenth O2- site, O2- is bonded in a 4-coordinate geometry to one Y3+, two Ag1+, and one I5+ atom. The O–I bond length is 1.87 Å. In the eleventh O2- site, O2- is bonded in a 4-coordinate geometry to one Y3+, two Ag1+, and one I5+ atom. The O–I bond length is 1.84 Å. In the twelfth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Y3+, one Ag1+, and one I5+ atom. The O–I bond length is 1.86 Å. In the thirteenth O2- site, O2- is bonded in a 1-coordinate geometry to one Y3+, one Ag1+, and one I5+ atom. The O–I bond length is 1.85 Å. In the fourteenth O2- site, O2- is bonded in a 1-coordinate geometry to two Ag1+ and two I5+ atoms. There are one shorter (1.83 Å) and one longer (2.61 Å) O–I bond lengths. In the fifteenth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to two Ag1+ and one I5+ atom. The O–I bond length is 1.84 Å. In the sixteenth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Y3+ and one I5+ atom. The O–I bond length is 1.86 Å. In the seventeenth O2- site, O2- is bonded in a 1-coordinate geometry to one I5+ atom. The O–I bond length is 1.85 Å. In the eighteenth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Y3+ and one I5+ atom. The O–I bond length is 1.84 Å. In the nineteenth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Y3+ and one I5+ atom. The O–I bond length is 1.86 Å. In the twentieth O2- site, O2- is bonded in a distorted single-bond geometry to one I5+ atom. The O–I bond length is 1.84 Å. In the twenty-first O2- site, O2- is bonded in a distorted single-bond geometry to one I5+ atom. The O–I bond length is 1.83 Å. In the twenty-second O2- site, O2- is bonded in a 3-coordinate geometry to one Y3+, one Ag1+, and one I5+ atom. The O–I bond length is 1.86 Å. In the twenty-third O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Y3+ and one I5+ atom. The O–I bond length is 1.82 Å. In the twenty-fourth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Y3+ and one I5+ atom. The O–I bond length is 1.84 Å. There are eight inequivalent I5+ sites. In the first I5+ site, I5+ is bonded in a 6-coordinate geometry to three O2- atoms. In the second I5+ site, I5+ is bonded in a 3-coordinate geometry to three O2- atoms. In the third I5+ site, I5+ is bonded in a 4-coordinate geometry to three O2- atoms. In the fourth I5+ site, I5+ is bonded in a 3-coordinate geometry to four O2- atoms. In the fifth I5+ site, I5+ is bonded in a 3-coordinate geometry to three O2- atoms. In the sixth I5+ site, I5+ is bonded in a 6-coordinate geometry to three O2- atoms. In the seventh I5+ site, I5+ is bonded in a 3-coordinate geometry to three O2- atoms. In the eighth I5+ site, I5+ is bonded in a 4-coordinate geometry to three O2- atoms.
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