Robert V. Hess

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. >

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).

Experiments and Theory for Continuous Steady Acceleration of Low Density Plasmas

Continuous plasma acceleration has been experimentally achieved between coaxial electrodes with the use of magnetic field gradients. The axial component of the magnetic field aids in ionizing the gas by lengthening the path of the electrons for collisions, as in the Philips ionization gauge. This axial component is also instrumental in the axial plasma acceleration. It interacts with the radial current to produce a circular component of electron motion exceeding by far that of the ions particularly at low densities. The circular Hall currents, together with the radial component of the magnetic field cause an axial force for plasma acceleration. The circular currents interacting with the axial magnetic field component cause an inward confining force on the plasma. For higher densities, the whole plasma is set into rotation. The circular currents yielding acceleration and confinement of the plasma are due to centrifugal forces pushing the plasma against the magnetic field.

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.

CO2 lidar For Measurements Of Trace Gases And Wind Velocities

The development of CO2 Lidar is important for a wide range of remote sensing applications involving trace gas concentrations (using Differential Absorption Lidar) and the effects of atmospheric dynamics on trace gas transport, meteorology, and aviation safety (using Doppler Lidar). The purpose of this paper is to discuss the CO2 Lidar systems technology and signal processing requirements based on measurement needs and measurement sensitivity studies for ground, aircraft and space platforms.

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.

Evaluation of catalyst for closed cycle operation of high energy pulsed CO2 lasers

Several catalyst materials have been tested for efficiency of converting CO and 02 to CO2 for use in a high energy CO2 laser. The composition of the gas mixtures was monitored by mass spectrometry and gas chromatography. A copper/copper oxide catalyst and a platinum/ tin oxide catalyst were used for closed cycle operation of a CO2 laser (0.7 joules/pulse), operating at 10 pulses per second.

Development In Tunable Solid State Lasers With High Spectral Purity, High Efficiency And Long Lifetime For Differential Absorption Lidar

The paper presents a review of tunable vibronic solid state lasers for DIAL measurements and provides new experimental results for tunable Ti:Sapphire lasers, materials development and spectral bandwidth narrowing through injection control. The Ti:Sapphire laser materials study indicates promise for reducing undesirable absorption in the lasing region to below 1% per cm. Pulsed injection control of a Ti:Sapphire laser with a 2.5 pm narrow band pulsed dye laser and with a Ti:Sapphire laser is demonstrated with near to complete energy extraction, indicating homogeneous line broadening. The review covers the status of tunable solid state lasers in the wavelength ranges around 1.6 and 2.3 μM for DIAL measurement of important trace gases such as CH4 and CO and development needs for lasers with reduced cryogenic cooling needs. Ti:Sapphire and Alexandrite lasers are compared as lasers for DIAL measurements of H2O vapor and pressure and temperature at ≈ 720, 940, and 760 nm. The effects of laser gain on optical damage, energy extraction and amplified spontaneous emission are indicated for several tunable lasers.