Thanh Le

A 10 GHz optoelectronic oscillator with continuous frequency tunability and low phase noise

A 10 GHz optoelectronic oscillator (OEO) with continuous frequency tunability and low phase noise is presented. By means of coarse tuning (selecting different RF filter) and fine tuning (tuning control voltage of phase shifter), we demonstrated the OEO can operate at any frequency on X-band (/spl sim/10 GHz, and any frequency. on the interested frequency range up to at least 45 GHz) with very low phase noise.

One-liter Hg ion clock for space and ground applications

We describe the development of a small Hg/sup +/ ion clock suitable for space use. A small clock occupying 1-2 liters volume and producing stability of 10/sup -12///spl radic//spl tau/ would significantly advance the state of space-qualified atomic clocks. Based on recent measurements, this technology should produce long-term stability as good as 10/sup -15/.

A solid state ultraviolet lasers based on cerium-doped LiCaAlF6 crystal resonator

We report the first demonstration of a UV laser using a high-Q whispering gallery mode (WGM) resonator of Ce3+: LiCaAlF6. We show that WGM resonators from LiCaAlF6 can achieve a Q of 2.6 x 107 at UV. We demonstrated a UV laser at 290 nm with a pulsed pump laser at 266 nm. The experiments showed the low pump threshold intensity of 7.5 x 109 W/m2 and slope efficiency of 25%. We have also observed lasing delay dynamics. These results are consistent with our modeling and theoretical estimates, and pave the way for a low threshold cw UV laser using WGM resonator cavity.

Hg ion atomic clock for deep space navigation and science

We have recently completed a breadboard ion-clock physics package based on Hg ions shuttled between a quadrupole and a 16-pole rf trap. With this architecture we have demonstrated short-term stability ~1-2x10-13 at 1 second, averaging to 10-15 at 1 day. This development shows that H-maser quality stabilities can be produced in a small clock package, comparable in size to an ultra-stable quartz oscillator required for holding 1-2x10-13 at 1 second. This performance was obtained in a sealed vacuum configuration where only a getter pump was used to maintain vacuum. The vacuum tube containing the traps has now been under sealed vacuum conditions for nearly two years with no measurable degradation of ion trapping lifetimes or clock short-term performance. We have fabricated the vacuum tube, ion trap and UV windows from materials that will allow a ~ 400°C tube bake-out to prepare for tube seal-off. This approach to the vacuum follows the methods used in flight vacuum tube electronics, such as flight TWTAs where tube operation lifetime and shelf life of up to 15 years is achieved. We use neon as a buffer gas with 2-3 times less pressure induced frequency pulling than helium and, being heavier, negligible diffusion losses will occur over the operation lifetime.