Michael G. Littman

Spectrally narrow pulsed dye laser without beam expander

We have developed a simplified version of the side-pumped pulsed dye laser which has a spectral halfwidth of 1.25 GHz and a peak power of 10 kW at 600 nm. The basic laser consists of only four components (output mirror, dye cell, diffraction grating, and tuning mirror) and is exceptionally easy to align. Since the beam expander has been eliminated, the laser cavity can be made quite compact. Under the condition of reduced gain, the laser has been operated in a single mode.

Novel geometry for single-mode scanning of tunable lasers

We describe a geometry that allows for the single-mode scanning of lasers that use a diffraction grating as the dispersive element. It is observed that under the right conditions a rotation of the tuning element can provide changes simultaneously in cavity length and diffraction angle that exactly match the requirements needed for continuous single-mode scanning. As a case study, the method is applied to the grazing-incidence pulsed dye laser.

Single-mode operation of grazing-incidence pulsed dye laser

A variation of the grazing-incidence pulsed dye laser is presented. This laser has been operated in a single longitudinal cavity mode with a single-shot linewidth of less than 300 MHz and a time-averaged linewidth of 750 MHz. The single-mode conversion efficiency of the laser is 2% using Rhodamine 6G dye.

EXTRASOLAR PLANET FINDING VIA OPTIMAL APODIZED-PUPIL AND SHAPED-PUPIL CORONAGRAPHS

In this paper we examine several different apodization approaches to achieving high-contrast imaging of extrasolar planets and compare different designs on a selection of performance metrics. These approaches are characterized by their use of the pupils transmission function to focus the starlight rather than by masking the star in the image plane as in a classical coronagraph. There are two broad classes of pupil coronagraphs examined in this paper: apodized pupils with spatially varying transmission functions and shaped pupils, whose transmission values are either 0 or 1. The latter are much easier to manufacture to the needed tolerances. In addition to comparing existing approaches, numerical optimization is used to design new pupil shapes. These new designs can achieve nearly as high a throughput as the best apodized pupils and perform significantly better than the apodized square aperture design. The new shaped pupils enable searches of 50%-100% of the detectable region, suppress the stars light to below 10-10 of its peak value, and have inner working distances as small as 2.8λ/D. Pupils are shown for terrestrial planet discovery using square, rectangular, circular, and elliptical apertures. A mask targeted at Jovian planet discovery is also presented, in which contrast is given up to yield greater throughput.

Laser cavity for generation of variable-radius rings of light

We report a laser cavity that has a ring as its output mode. The radius of the ring can be scanned by tuning the laser frequency. This design can be implemented in any tunable laser with large gain and can be useful when ring illumination patterns are needed. As an example, we demonstrate this new cavity configuration by using a side-pumped grazing-incidence dye laser.

Single-mode pulsed tunable dye laser

The specifications are given for an updated version of the grating incidence puled dye laser. (AIP)

Optimal one-dimensional apodizations and shaped pupils for planet finding coronagraphy

The realization that direct imaging of extrasolar planets could be technologically feasible within the next decade or so has inspired a great deal of recent research into high-contrast imaging. We have contributed several design ideas, all of which can be described as shaped pupil coronagraphs. We offer a complete and unified survey of one-dimensional shaped pupil designs, some of which have been published in our previous papers. We also introduce a promising new design, which we call bar-code masks. With these masks we can achieve the required contrast with a fairly large discovery zone and throughput, but most importantly they are perhaps the easiest to manufacture and might therefore stand up best to refined analyses.

Focused bulk ultrasonic waves generated by ring‐shaped laser illumination and application to flaw detection

Focused bulk ultrasonic waves have been generated in aluminum plates by surface irradiation with ring‐shaped laser light. The waves are detected by a piezoelectric transducer. Compression and shear peak amplitudes drop quickly when the detector is moved away from the epicenter. This shows that strong focusing exists at the epicenter as the result of constructive interference of the waves generated by different parts of the ring. The focusing persists when the radius of the laser light is scanned over a large range, indicating that the elastic disturbance concentrates in depth along the ring’s central axis. Numerical simulations are presented for comparison. The ‘‘pencil‐like’’ acoustic wave structure is used to observe a sample plate with an artificial flaw. Strong new features including compress‐shear mode conversion at the site of the flaw are observed. These features are used to locate the flaw within the sample.

Shaped pupil coronagraphs for planet finding: optimization, manufacturing, and experimental results

Current plans call for the first Terrestrial Planet Finder mission, TPF-C, to be a monolithic space telescope with a coronagraph for achieving high contrast. Our group at Princeton pioneered the concept of shaped pupils for high contrast imaging and planet detection. In previous papers we introduced a number of families of optimal shaped pupils in square, circular, and elliptical apertures. Here, we show our most promising designs and present our laboratory results for the elliptical shaped pupil. We are currently achieving better than 10−7 contrast at 10 λ/D and 10−5 contrast at 4 λ/D, without wavefront control. We describe the deep ion etching manufacturing process to make free standing masks. We also discuss what is limiting contrast in the laboratory and our progress in wavefront correction.

Optimal control of the electric susceptibility of a molecular gas by designed nonresonant laser pulses of limited amplitude

We present a theoretical study on optimal control of the electric susceptibility change of a homogeneous molecular gas resulting from orientational anisotropy induced by nonresonant lasers with limited intensity. It is assumed that the molecular gas is initially in thermal equilibrium. Two types of optimal control objectives have been considered: terminal control and temporal profile control (i.e., trajectory control). A step function is introduced into the cost functionals which successfully helps to realize the restriction on the magnitude of the field amplitude in numerical optimization, as demonstrated by the examples. Calculations are carried out for CS2 which has a small rotational constant (B=0.1091 cm−1) and a quite large polarizability anisotropy (Δα=9.6 A3). For terminal control of a maximal susceptibility change at a target time T, it is found that the optimal control field is composed of a series of rectangular pulses with identical amplitudes equal to a preassigned bound value. All of the opt...