Dual Wavelength Injection-Locked Pulsed Ring Laser with Improved Noise Immunity, 18-R8168
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 resonance 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 resonance ionization technique selectively ionizes specific atoms or molecules by exciting them with specific wavelengths of laser light simultaneously, identifying specific isotopes. 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 has developed a unique laser system that has the capability of producing two wavelengths simultaneously, generating Fourier transform limited output, and providing stable output with immunity from mechanical vibration throughout the acoustic range. The system has the potential to reduce the number of lasers systems 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 wavelengths of the laser system is provided by two independent seed lasers that are injected into the cavity via the output coupling mirror and propagate within the ring laser cavity. Enhanced noise immunity and the ability to achieve Fourier-transform limited laser output on every pulse is accomplished with the use of an electro-optic crystal and a Ramp-Hold-Fire cavity control technique, which mode matches the amplifier cavity with the seed laser. The laser system and techniques under development represent a substantial step forward in dual wavelength and pulsed laser design.
Accomplishments — SwRI has successfully developed a dual wavelength ring laser system that is immune to noise throughout the acoustic range, see Figure 1. Single- and dual-wavelength seeded output, at the Fourier-transform limited output, has been demonstrated, as illustrated in Figures 2 and 3. The ability to drive the 780 nm (D2) and 776 nm transitions in Rubidium 87 has also been demonstrated, as shown in Figure 4. In addition, the capability to simultaneously produce multiple, discrete laser output is possible, as illustrated in Figure 5. The results of this work were recently presented at the Frontiers in Optics 2011 conference and the SPIE Photonics West 2012 conference. Work is complete and papers have been presented.
