Laser Beam Steering Along Three-Dimensional Paths

AbstractThe study of microstructure evolution in additive manufacturing of metals would be aided by knowing the thermal history. Since temperature measurements beneath the surface are difficult, estimates are obtained from computational thermo-mechanical models calibrated against traces left in the sample revealed after etching, such as the trace of the melt pool boundary. Here we examine the question of how reliable thermal histories computed from a model that reproduces the melt pool trace are. To this end, we perform experiments in which one of two different laser beams moves with constant velocity and power over a substrate of 17-4PH SS or Ti-6Al-4V, with low enough power to avoid generating a keyhole. We find that thermal histories appear to be reliably computed provided that (a) the power density distribution of the laser beam over the substrate is well characterized, and (b) convective heat transport effects are accounted for. Poor control of the laser beam leads to potentially multiple three-dimensional melt pool shapes compatible with the melt pool trace, and therefore to multiple potential thermal histories. Ignoring convective effects leads to results that are inconsistent with experiments, even for the mild melt pools here.

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Analytical solution for a transient, three-dimensional temperature distribution due to a moving laser beam

International Journal of Heat and Mass Transfer ◽

10.1016/j.ijheatmasstransfer.2006.03.026 ◽

2006 ◽

Vol 49 (21-22) ◽

pp. 4124-4131 ◽

Cited By ~ 36

Author(s):

Guillermo Araya ◽

Gustavo Gutierrez

Keyword(s):

Temperature Distribution ◽

Analytical Solution ◽

Laser Beam ◽

Three Dimensional

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Vertically integrated diffractive gratings on photonic crystal surface emitting lasers

Scientific Reports ◽

10.1038/s41598-021-82194-4 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Lih-Ren Chen ◽

Kuo-Bin Hong ◽

Hsiu-Ling Chen ◽

Kuan-Chih Huang ◽

Tien-Chang Lu

Keyword(s):

Photonic Crystal ◽

Crystal Surface ◽

Beam Steering ◽

Azimuthal Angle ◽

Three Dimensional ◽

Grating Period ◽

Single Chip ◽

Output Beam ◽

Optical Elements ◽

Emitting Lasers

AbstractWe designed and fabricated a photonic crystal surface emitting laser (PCSEL) with vertically integrated diffractive optical elements on their top to study the mechanism of static beam steering on a single chip. The deflected output beam by the self-formed periodic ITO cladding layer of the PCSEL can be further steered by changing the grating period and azimuthal angle of the diffractive gratings relative to the photonic crystal. Through the analysis of photonic band structure and lasing characteristics, the periodic ITO structure is coupled to the photonic crystal band, whereas the integrated grating serves the diffractive function only. The findings pave the way for the design of PCSELs enabling single or multiple output beam with varying direction capability. This type of laser is regarded as an ideal light source for various applications, such as light detection and ranging and three-dimensional sensing systems.

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Optical GNSS Receiver for the ESA's NGGM-MAGIC Mission and for LEO Satellites with the Highest Orbit Accuracy

10.5194/egusphere-egu21-9072 ◽

2021 ◽

Author(s):

Drazen Svehla

Keyword(s):

Laser Beam ◽

Gravity Field ◽

Carrier Phase ◽

Beam Steering ◽

Precise Orbit Determination ◽

Optical Carrier ◽

Gnss Receiver ◽

Cw Laser ◽

Leo Satellites ◽

Leo Satellite

Precise orbit determination (POD) of LEO satellites is done with a geodetic grade GPS receiver measuring carrier-phase between a LEO and GPS satellites, and in some cases this is supported with a DORIS instrument measuring Doppler between LEO and ground DORIS stations. Over the last 20 years we have demonstrated 1-2 cm accurate LEO POD and about 1 mm for inter-satellite distance. In order to increase the accuracy of the single satellite POD or satellites in LEO formation we propose an &#8220;optical GNSS receiver&#8221;, a cw-laser on a LEO satellite to measure Doppler between a LEO and GNSS satellite(s) equipped with SLR arrays and to develop it for the next gravity field mission.&#160;&#160;&#160;&#160; &#160;The objective of the ESA mission NGGM-MAGIC (Next Generation Gravity Mission - Mass-change and Geosciences International Constellation) is the long-term monitoring of the temporal variations of Earth&#8217;s gravity field at high resolution in time (3 days) and space (100 km), complementing the GRACE-FO mission from NASA at 45&#176; orbit inclination. Currently, the GRACE-type mission design is based on optical carrier-phase measurements between two LEO satellites flying in a formation and separated by 200 km.We propose an extension of the GRACE-type LEO-LEO concept by the &#8220;optical GNSS receiver&#8221; to provide Doppler measurements between a LEO satellite and GNSS satellite(s) equipped with SLR corner cubes by means of a cw-laser onboard a LEO satellite. Such a &#8220;vertical&#8221; LEO-GNSS observable is missing in the classical GRACE-type LEO-LEO concept. If Doppler measurements are carried out from the two GRACE-type satellites in the LEO orbit to the same GNSS satellite and by forming single-differences to that GNSS satellite one can remove any GNSS-orbit related error in the measured LEO-GNSS Doppler. In this way, radial orbit difference can be obtained between the two GRACE-type satellites (free of all GNSS orbit errors) and complement &#8220;horizontal&#8221; LEO-LEO measurements between the two GRACE-type satellites in the LEO orbit.The non-mechanical laser beam steering has been developed for an angle window of -40&#176; to +40&#176; and it does not require a rotating and a big telescope in LEO (no clouds and atmosphere turbulences in LEO). Therefore, in such a beam-steering window, one could always observe with a fiber cw-laser one GNSS satellite close to the zenith from both GRACE-type satellites. The non-mechanical beam steering concept in zenith direction can be supported by a small 10-cm like (fixed) Ritchey-Chr&#233;tien telescope (COTS), a Cassegrain reflector design widely used for LEO satellites, e.g., for James Webb Space Telescope or for an optical Earth imaging with Cubesats with the 50 cm resolution.Considering that several GNSS satellites in the field of view could be observed from a LEO satellite with this approach (including LAGEOS-1/2 and Etalon satellites) and the non-mechanical laser beam steering could be extended towards the LEO horizon, an &#8220;optical&#8221; GNSS receiver is a new concept for POD of LEO satellites. Here, we provide simulations of this new concept for LEO POD with GNSS/SLR constellations equipped with SLR arrays and discuss all new applications this new concept could bring.

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