Engineering topics

Lim, Lawrence

Publications and source records attributed to Lim, Lawrence.

4 records

NASA NTRS2007

Cold Atom Source Containing Multiple Magneto-Optical Traps

An apparatus that serves as a source of a cold beam of atoms contains multiple two-dimensional (2D) magneto-optical traps (MOTs). (Cold beams of atoms are used in atomic clocks and in diverse scientific experiments and applications.) The multiple-2D-MOT design of this cold atom source stands in contrast to single-2D-MOT designs of prior cold atom sources of the same type. The advantages afforded by the present design are that this apparatus is smaller than prior designs.

Ramirez-Serrano, Jaime↗

NASA NTRS2007

Compact Microwave Mercury Ion Clock for Deep-Space Applications

We have recently completed a breadboard ion-dock physics package based on Kg ions shuttled between a quadrupole and a 16-pole rf trap. With this architecture we have demonstrated short-term stability -1-2xl0-13 at 1 second, averaging to 10-15 at 1 day. This development shows that 8- maser quality stabilities can be produced in a small clock package, comparable in size to an oItra-stable quartz oscillator required for holding 1-2xl0-13 at 1 second. This performance was obtained in a sealed vacuum configuration where only agetter pump was used to maintain vacuum. The vacuum tube containing the traps has now been onder 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 sealoff. This approach to the vacuum follows the methods used in mght vacuum tube electronics, such as flight TWTA's 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, negligable diffusion losses will occur over the operation lifetime.

space clock↗

NASA NTRS2006

Miniaturized Mercury Ion Clock for Ultrastable Deep Space Applications

We have recently completed a prototype 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 ~2-3x10-13 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 1.5 years with no measurable degradation of ion trapping lifetimes or clock short-term performance. Because the tube is sealed, the Hg source and Neon buffer gas are held indefinitely, for the life of the tube. There is no consumption of Hg in this system unlike in a Cs beam tube where lifetime is often limited by Cs depletion.

mercury ion clocks↗

NASA NTRS2004

Progress towards a space-borne quantum gravity gradiometer

Quantum interferometer gravity gradiometer for 3D mapping is a project for developing the technology of atom interferometer-based gravity sensor in space. The atom interferometer utilizes atomic particles as free fall test masses to measure inertial forces with unprecedented sensitivity and precision. It also allows measurements of the gravity gradient tensor components for 3D mapping of subsurface mass distribution. The overall approach is based on recent advances of laser cooling and manipulation of atoms in atomic and optical physics. Atom interferometers have been demonstrated in research laboratories for gravity and gravity gradient measurements. In this approach, atoms are first laser cooled to micro-kelvin temperatures. Then they are allowed to freefall in vacuum as true drag-free test masses. During the free fall, a sequence of laser pulses is used to split and recombine the atom waves to realize the interferometric measurements. We have demonstrated atom interferometer operation in the Phase I period, and we are implementing the second generation for a complete gradiometer demonstration unit in the laboratory. Along with this development, we are developing technologies at component levels that will be more suited for realization of a space instrument. We will present an update of these developments and discuss the future directions of the quantum gravity gradiometer project.

laser cooling↗