The primary objective of the Mars Observer laser altimeter (MOLA) investigation is to determine globally the topography of Mars at a level suitable for addressing problems in geology and geophysics. Secondary objectives are to characterize the 1064-nm wavelength surface reflectivity of Mars to contribute to analyses of global surface mineralogy and seasonal albedo changes, to assist in addressing problems in atmospheric circulation, and to provide geodetic control and topographic context for the assessment of possible future Mars landing sites. The principal components of MOLA are a diode-pumped, neodymium-doped yttrium aluminum garnet laser transmitter that emits 1064-nm wavelength laser pulses, a 0.5-m-diameter telescope, a silicon avalanche photodiode detector, and a time interval unit with 10-ns resolution. MOLA will provide measurements of the topography of Mars within approximately 160-m footprints and a center-to-center along-track foot print spacing of 300 m along the Mars Observer subspacecraft ground track. The elevation measurements will be quantized with 1.5 m vertical resolution before correction for orbit- and pointing induced errors. MOLA profiles will be assembled into a global 0.2 deg x 0.2 deg grid that will be referenced to Mars' center of mass with an absolute accuracy of approximately 30 m. Other data products will include a global grid of topographic gradients, corrected individual profiles, and a global 0.2 deg x 0.2 deg grid of 1064-nm surface reflectivity.

http://www-geodyn.mit.edu/zubersite/pdfs/Zuber_97JGR1992b.pdf

The Mars Observer laser altimeter investigation

The spectroscopic and laser kinetic properties of the trivalent ytterbium ion in various solid-state media are reviewed. Contrasts between four- and quasi-three-level lasers (e.g., Nd:YAG versus Yb:YAG) are highlighted. Various architectures suitable for use in high-brightness high-power Yb:YAG lasers are examined, and achieved laser performance levels are summarized. The properties of alternative ytterbium-doped laser gain media are reviewed, and early laser results are cited.

Ytterbium solid-state lasers. The first decade

Ytterbium solid-state lasers: The first decade

A plurality of the areas of different light reflectivity of a bar code symbol, or the like, are simultaneously illuminated, using, e.g., a beam of laser light that has an elongated cross-section. The laser light beam is swept over the symbol in a direction transverse to the elongated dimension of the illuminated region so that a two-dimensional area of the symbol is illuminated over time, until the symbol is read. The light that reflects from the illuminated region of the symbol is imaged on a linear sensor array, which is then scanned or read out to produce signals representative of spatial intensity variations of the imaged light along a linear path in the field of view.

Method and apparatus for reading two-dimensional bar code symbols with an elongated laser line

Diode laser-pumped solid-state lasers are efficient, compact, all solid-state sources of coherent optical radiation. Major advances in solid-state laser technology have historically been preceded by advances in pumping technology. The helical flash lamps used to pump early ruby lasers were superseded by the linear flash lamp and arc lamp now used to pump neodymium-doped yttrium-aluminum-garnet lasers. The latest advance in pumping technology is the diode laser. Diode laser-pumped neodymium lasers have operated at greater than 10 percent electrical to optical efficiency in a single spatial mode and with linewidths of less than 10 kilohertz. The high spectral power brightness of these lasers has allowed frequency extension by harmonic generation in nonlinear crystals, which has led to green and blue sources of coherent radiation. Diode laser pumping has also been used with ions other than neodymium to produce wavelengths from 946 to 2010 nanometers. In addition, Q-switched operation with kilowatt peak powers and mode-locked operation with 10-picosecond pulse widths have been demonstrated. Progress in diode lasers and diode laser arrays promises all solid-state lasers in which the flash lamp is replaced by diode lasers for average power levels in excess of tens of watts and at a price that is competitive with flash lamp-pumped laser systems. Power levels exceeding 1 kilowatt appear possible within the next 5 years. Potential applications of diode laser-pumped solid-state lasers include coherent radar, global sensing from satellites, medical uses, micromachining, and miniature visible sources for digital optical storage.

http://science.sciencemag.org/content/sci/239/4841/742.full.pdf

Diode laser--pumped solid-state lasers.

A plurality of diode lasers is focussed onto a single region by arranging the diodes at equally spaced locations on a first arc. Each diode laser emits light in a slit-like pattern which is characterized by orthogonal axes. In a first group of cylindrical lenses, one associated with each diode laser, each lens has a refractive surface having an axis parallel to one of the emitting axes of the laser and refracts light to a focal region of defined dimensions. Each cylindrical lens is disposed along a second arc having a circular center common with the first arc. A second group of cylindrical lenses, one associated with each laser, is also disposed on a circular arc, concentric with the other arcs, but the second group has a refractive axis perpendicular to the first refractive axis. The second group of cylindrical lenses acts upon the second axis of the source image, focussing it to the common focal region. The first and second cylindrical lens groups may be combined into a toric surface within a single lens. The cylindrical lenses may either be individual lenses, or may be combined into a lenticular array. The lenses may be simple cylindrical refractive lenses, Fresnel lenses, or holographic lenses. A bright image of the source is formed at the common focal region. The diode lasers and cylindrical lenses may be arranged in three dimensions to produce very high optical power densities.

Diode laser arrangement forming bright image

A diode laser array assembly made from a plurality of linear diode laser array subassemblies stacked one above the other. Each subassembly is an array of individual laser beam emitters, such as a laser bar, mounted on a support plate. An electrically conductive path goes from one major surface of a support plate, through the linear laser array, to an opposite major surface of the support plate. Each subassembly is connected physically and electrically to adjacent subassemblies to form the final assembly. In one embodiment, the support plates are electrically insulating and partly coated or covered with conducting material. The plates are either rectangular with projections and directly connected, rectangular with metal plates between each other, or rectangular and connected in a staircase configuration. Alternatively, the support plates may be electrically conducting with an insulating layer and a conducting layer disposed in a sandwich configuration. The plates may also be made up of an electrically insulating support plate and an electrically conducting spacer plate.

Stacked diode laser array assembly

A laser array submount structure for assembly into a two-dimensional stacked array with precise separation between laser diodes of adjacent submounts. The submount includes a deformable metal layer, such as a soft solder, on one major surface of a laser array support plate. A spacer element having spaced apart ridges is disposed on the opposite major surface. A laser diode array is mounted on a front edge of the support plate. In a cold bonding step, submounts are pressed together causing ridges to penetrate the deformable metal layer to a specified depth. The displaced metal spreads into channels between the ridges, allowing pressing of multiple laser array submounts into stackes of precise total tolerance.

Ribbed submounts for two dimensional stacked laser array

Continuous‐wave output power levels of 38 W from one facet have been obtained from a 1 cm monolithic AlGaAs laser array with a 2 mm total active aperture width. One of the diodes has been operated under constant current conditions (initial output power of 5 W) at room temperature for over 1100 h.

Ultrahigh power 38 W continuous‐wave monolithic laser diode arrays

The power available from transistor-sized semiconductor diode lasers has increased rapidly in recent years, more than doubling every year. Continuous outputs of several watts and pulsed powers in the kilowatt range with 50 percent overall efficiency are now possible with these compact devices. These developments may signal the start of a technological advancement in optics comparable to the solid-state revolution in electronics 20 years ago.

https://science.sciencemag.org/content/sci/237/4820/1305.full.pdf

Gary L. Harnagel

Papers

Diode laser arrangement forming bright image

Stacked diode laser array assembly

Ribbed submounts for two dimensional stacked laser array

Ultrahigh power 38 W continuous‐wave monolithic laser diode arrays

Ultrahigh-power semiconductor diode laser arrays.