Philip Brockman

Coherent lidar airborne wind sensor II: flight-test results at 2 and 10 μm

The use of airborne laser radar (lidar) to measure wind velocities and to detect turbulence in front of an aircraft in real time can significantly increase fuel efficiency, flight safety, and terminal area capacity. We describe the flight-test results for two coherent lidar airborne shear sensor (CLASS) systems and discuss their agreement with our theoretical simulations. The 10.6-μm CO(2) system (CLASS-10) is a flying brassboard; the 2.02-μm Tm:YAG solid-state system (CLASS-2) is configured in a rugged, light-weight, high-performance package. Both lidars have shown a wind measurement accuracy of better than 1 m/s.

High resolution spectral measurement of the HNO 3 11.3-μm band using tunable diode lasers

High resolution spectra in the region of the 2nu(9) band of nitric acid have been obtained for selected portions of the HNO(3) spectrum using tunable diode laser techniques. Continuous spectra are presented from 891.25 cm(-1) to 898.77 cm(-1), with a spectral resolution </=0.001 cm(-1) (30 MHz). Absolute line intensities and line positions are presented. Absolute wavelength calibration was obtained by frequency mixing the diode laser with a C(13)O(2)(16) isotope laser. Self and foreign gas (N(2)) broadening coefficients were iteratively calculated from the experimental data and were determined to be alpha(a) = 0.8 cm(-1)/atm and alpha(f) = 0.13 cm(-1)/atm, respectively.

Pulsed injection control of a titanium-doped sapphire laser

Injection control of a tunable Ti:sapphire laser using a narrow-bandwidth pulsed dye laser operating at a wavelength removed from the peak of the Ti:sapphire-laser gain curve is reported. The free-running Ti:sapphire laser had broadband laser emission from 750 to 790 nm. Injection at 727 nm resulted in essentially complete energy extraction at that wavelength in a 2.5-pm bandwidth matching the injection source.

Demonstration of frequency control and CW diode laser injection control of a titanium-doped sapphire ring laser with no internal optical elements

Theoretical and experimental frequency narrowing studies of a Ti-sapphire ring laser with no intracavity optical elements are reported. Frequency narrowing has been achieved using a birefringent filter between a partially reflecting reverse wave suppressor mirror and the ring cavity output mirror. Results of CW diode laser injection seeding are reported. >

Temperature distribution in side- and end-pumped laser crystal rods: temporal and spatial variations

Knowledge of the temperature distribution of laser rods end pumped by laser diodes or other laser systems is relevant when thermal stress and crystal damage are expected. The temperature of a multipulsed or continuously pumped laser rod is given as a double-series expression and as a function of time. The mathematical model considers all surface cooling rates, the spatial and temporal variations of the pump beam, and the specific heat and thermal conductivity of the rod material. This eigenfunction expansion representation was employed to predict the spatial and time-dependent quasi-steady-state temperature in Ti:sapphire, Nd:YAG, and Cr:LiSAF laser rods of specific dimensions.

Investigation of 2.1-μm lasing properties of Ho:Tm:Cr:YAG crystals under flash-lamp pumping at various operating conditions

Flash-lamp-pumped normal-mode and Q-switched 2.1-microm 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 more than the normal-mode laser energies were obtained in the form of a strong single spike by optimizing 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. % at operating temperatures from 120 K to near room temperature. Laser transitions were observed only at 2.098 and 2.091 microm under various conditions. The 2.091-microm laser transition appeared to be dominant at high-temperature operations with low-reflective-output couplers and to have an energy-level assignment from 5313 cm(-1) to 534 cm(-1) or (and) from 5313 cm(-1) to 536 cm(-1).

Recent advances in efficient long-life, eye-safe solid state and CO2 lasers for laser radar applications

There is increasing interest in the comparative roles of CO2 and the more recently developed eye-safe solid-state lasers for long-life efficient laser radar applications. This paper assesses recent technology advances in each area and their roles in laser radar and especially Doppler lidar and DIAL development. The key problems in eye-safe solid-state lasers are discussed relating to the energy transfer mechanisms between the complicated energy level manifolds of the Tm,Ho,Er ion dopants in hosts with decreasing crystal fields such as YAG or YLF. One concerns optimization of energy transfer for efficient lasing through choice of dopant concentration, power density, crystal field and temperature, with the highly practical goal of minimal cooling needs. Another key problem, specific to laser radar and lidar, involves tailoring of energy transfer times to provide efficient energy extraction for short, e.g., Q-switched pulses used in DIAL and Dopper lidar. Special emphasis is given to eye-safe lasers in the 2 μm range because of the high efficiency applications to DIAL and (windshear) Doppler lidar and because they are well suited for Optical Parametric Oscillator frequency conversion into the important ≈ 4 to 5 μm DIAL range. The discussion of CO2 lasers concerns recent advances in Pt/Sn02 oxide catalysts and other noble metal/metal oxide combinations. Emphasis is given to the dramatic effects of small quantities of H20 vapor for increasing the activity and lifetime of Pt/Sn02 catalysts and to increased lifetime operation with rare isotope 12C18O2 lasing mixtures; iL-the 12C18O2 laser wavelengths in the 9.1 μm range are of special interest for space-based Doppler lidar such as the proposed Laser Atmospheric Wind Sounder.

Alexandrite Laser Pumped Ho:Tm:YLF Laser Performance

The performance of Ho:Tm:YLF pumped by an Alexandrite laser was compared to previously obtained results for comparable Ho:Tm:YAG experiments. We have used an Alexandrite laser with pulse durations of 650μs and 200μs to longitudinally pump Ho:Tm:YLF crystal with 1.5% and 0.5% Ho concentration and length of 4 to 6mm. For a 1.5% Ho concentration in YLF, with pump pulse of 200μs, a slope efficiency as high as 50% is obtained for 6mm long crystal. In general, higher slope efficiencies are achieved in Ho:Tm:YLF than in Ho:Tm:YAG. Previous Ho:Tm:YAG experimental measurements are in good agreement with an improved rate equation model.

Injection Controlled Titanium Doped Sapphire Laser Using a Pulsed Dye Laser

Titanium-doped sapphire (Ti:sapphire) lasers have been extensively studied since their recent introduction [1–3]. Because of their wide tuning range (≈700 to 1000 nm), Ti:sapphire lasers are candidates for remote lidar measurements of H2O vapor (≈720 and 940 nm) and pressure and temperature (≈760 nm). These measurements require efficient narrow bandwidth operation and accurate wavelength control.

Laser remote sensing in atmospheric sciences, aviation safety, aeronautical research, and experiments from space platforms and high-flying aircraft

Traditionally, the term laser remote sensing has been associated with active, optical measurements of the Earth’s atmosphere, lands, and oceans. In this paper, we concentrate our overview of laser remote sensing upon the Earth’s atmosphere in three disciplines: Atmospheric sciences, aviation safety, and aeronautical research. In atmospheric sciences, laser remote sensing has played a prominent role in the measurement of clouds, aerosols, the planetary boundary layer, chemical species, metals and ions, and in atmospheric dynamics in the temporal tracking of physical parameters and the direct measurement of atmospheric winds. Quite recently, laser remote sensing has been especially effective in correlative studies from ground and airborne platforms related to scientific studies in the eruption of Mount Pinatubo, and in following the dispersion of associated aerosols in the atmosphere, both in latitude and longitude. Laser remote sensing has also been very effective in studies related to the formation of the ozone hole, in the antarctic and arctic regions. Range-resolved measurements of atmospheric ozone have been made which track “in real time” the formation of the ozone hole and its subsequent dissipation. Laser measurements of the depolarization ratio of backscattering from particulates in the region of the ozone hole where Polar Stratospheric Clouds (PSC’s) form have provided unique information on the physics of the PSC’s and on the dynamics of the formation of the ozone hole phenomena. It is quite clear that laser remote sensing has proven to be an invaluable measurement technique for these types of chemistry investigations. The range-resolved measurement of atmospheric water vapor, correlated to the height of the planetary boundary layer and the distribution of aerosols over land and oceans, has also been demonstrated quite recently to be a unique measurement provided by laser remote sensing from aircraft. When this technique is developed from high flying aircraft and/or satellites, a major measurement technique will be available for the study of the hydrological cycle, globally. Soon, we should be seeing range-resolved measurements of atmospheric water vapor (50 meters) from a high-flying aircraft, with an accuracy better than 10 percent, as a routine measurement in atmospheric sciences. The historical evolution of laser remote sensing from the initial ground-based measurements of atmospheric aerosols in the early 1960’s to the sophisticated measurements from aircraft of today represent a unique evolution of technology in lasers and electrooptics, coupled to persistent attention to sound engineering development of a unique technique. For this paper, I have asked Dr. William B. Grant, a pioneer in laser remote sensing of the atmosphere, to provide this section entitled “Laser Remote Sensing in Atmospheric Sciences.“