Dual Wavelength Injection-Locked Pulsed Ring Laser with Improved Noise Immunity, 18-R8168

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Principal Investigators
Thomas Moore
F. Scott Anderson
Joseph Mitchell

Inclusive Dates:  07/01/10 – Current

Background - Interest in developing tunable laser systems that have the capability to produce two wavelengths of light simultaneously has intensified over the past several years. The motivation for developing dual-wavelength laser systems includes differential absorption lidar (DIAL), non-linear frequency mixing, pump-probe detection, and laser multi-photon ionization. Recently, work on developing a portable Laser Desorption Resonance Ionization Mass Spectrometer (LDRIMS) instrument by SwRI space researchers has led to a need for several specialized laser systems. The LDRIMS instrument will be used to perform geochronology and geochemistry measurements based on the ratios of certain rubidium (Rb) and strontium (Sr) isotopes. The multi-photon resonance ionization technique selectively ionizes specific atoms or molecules by exciting them with specific wavelengths of laser light simultaneously, identifying the atom or molecule. The LDRIMS system, as it exists today, requires seven laser systems that require a large amount of space and power. Developing a tunable laser with the capability to deliver two wavelengths simultaneously will significantly reduce the space and power requirements, avoid timing jitter issues among multiple systems, and decrease the burden of maintaining multiple laser systems.

Approach - SwRI is currently developing a unique laser system which has the capability of producing two wavelengths simultaneously, of operating near the Fourier transform limit, and of providing stable output with immunity from mechanical vibration throughout the acoustic range. The system has the potential to reduce the number of lasers needed by the LDRIMS system by approximately half and provides the capability to be ruggedized in a small portable package. To achieve these objectives, a Ti:sapphire ring laser design with a total path length of 50 cm is used to form a traveling wave oscillator. The traveling wave provides the capability to utilize the entire length of the Ti:sapphire laser crystal while eliminating standing modes. The ability to independently tune the two center wavelengths of the laser system is provided by two independent seed lasers which are injected into the cavity via the output coupling mirror and counter propagate within the ring laser cavity. Enhanced noise immunity and the ability to achieve the Fourier transform limit are accomplished with the use of a nonlinear electro-optic crystal and a Ramp-Hold-Fire cavity control technique. The laser system and techniques under development represent a substantial step forward in dual wavelength and pulsed laser design.

Accomplishments - SwRI has successfully completed the preliminary and detailed design of the ring laser system and of a novel External Cavity Diode Laser (ECDL) as seed laser systems. In addition, the fabrication and assembly of the ring laser and two seed lasers has been completed. SwRI has completed basic functional testing of the seed lasers and is preparing to begin functional testing of the ring laser. Furthermore, SwRI has demonstrated the ability of the seed lasers to drive the D2 transition of Rubidium 87 and demonstrated the ability to continuously tune the laser wavelength from 776 nm to 790 nm.

Figure 1. Ring Laser Overview


Figure 1. Ring Laser Overview


Figure 2. Seed Laser


Figure 2. Seed Laser


Figure 3. Seed Laser Design


Figure 3. Seed Laser Design


Figure 4. Rb87 D2 Resonance Transition


Figure 4. Rb87 D2 Resonance Transition


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