The planned purchase of upgraded APD's has been put on hold pending comparative tests between old and new technology APD's (a sample new APD is on loan from the JNLT). Initial estimates of potential gains in sensitivity appear to be overly optimistic. A single APD in the Wavefront Sensor failed and was replaced by a spare.
Optical throughput efficiency calculations of the wavefront sensor subsystem predict a factor of 2.6 higher sensitivity than is measured on the sky, and in the laboratory. Attempts to locate the source of this loss have been unsuccessful to date.
Tests of the 2x focal enlarger for the AOB using FOCAM and STIS were very successful. The system provides critical sampling of the psf below 1.0 µm. This system is now an available option for observers.
The focal enlarger was also modified slightly to accommodate our Fabry Perot etalons. The system was successfully tested on the AOB with a comparison spectral source earlier in the semester. We hope to test the combination on the sky in January.
Three new beamsplitters have been ordered for use in the visible with OASIS. The beamsplitters will have bandpasses for the V, R, and I bands These should improve throughput to the WFS by about 50% over the current '50/50' beamsplitter and will increase throughput in the science path to about 90% in the bandpass.
The diameter of the AOB's small artificial star was reduced from 8 microns to 3.0 microns for work at wavelengths in the 0.5 to 1.0 um range.
The user interface is now working quite well; the number of system glitches has been reduced to at most one or two a night. Still, substantial improvements to the software are underway to improve overall reliability. The MOSAIC tool used in combination with MONICA has been particularly successful.
Overall ease of use for visiting scientist - one of the initial design goals - has been validated by two observing runs by non-specialist observers. Guide star acquisition and loop closure have proven to be trouble free and straightforward. AOB specialists are no longer required on site once initial observer familiarization has taken place.
A large amount of background work by the technical staff has been aimed at making setup operationally "friendly" through hands-on training and updating of documentation.
Flexure measurements of the FTS in the BEAR configuration were made to determine if the modifications made to the mounting mechanics of the REDEYE camera had reduced image motion. Unfortunately the stiffer camera mount did not reduce motion in the image plane. The flexure data suggests that the major source of image motion, which reduces BEAR's effective FOV by about 10% for long scans, is probably in the optics between the output of the FTS and the REDEYE camera. The upgraded mechanics does however greatly ease the mounting and alignment of Redeye.
The newly re-coated IR1 beamsplitters were installed and worked well. Increasing problems with reference laser throughput for the IR2 beamsplitters caused several servo unlocks during the July / August observing run. Replacement beamsplitters are currently being fabricated (re-coating was not an option). The new beamsplitters should be ready in time for the next FTS runs. The reduced reference laser signal with the IR2 beamsplitters made switching between the beamsplitters difficult and required modifications to the reference signal circuitry.
A new "seismology mode", consisting of small scans (typically 16 steps) around a selected carriage position has been added..
MOS / OSIS controller software has been upgraded to eliminate several problems and to provide better test capabilities. In particular, problems with system hangups during OSIS fast guiding should now be solved.
A pair of high resolution IR grisms for OSIS have been received and are undergoing tests. We have also received a replacement for the low resolution H grism which was originally made out of specification.
New light baffles have been fabricated for MOS and OSIS. These should be installed by the end of October. These baffles will hopefully solve light leak problems at the edges of the Prontor shutters.
The inside of the OSIS camera barrel has been painted a flat black in an attempt to reduce the amount of scattered light seen in OSIS.
MOS / OSIS setup has represented a heavy load to the technical staff. A great deal of this load is associated with interchanges of grisms between cassettes. A first step in freezing each of the grisms to a specific cassette was started this semester with a contract to DAO for the manufacture of 11 grism cells .
Finally, bi-prism focus capabilities for OSIS and the MOS ARGUS mode has been provided by a pair of new bi-prisms.
As with MOS / OSIS, the spectrograph's DUCK control software has been updated to improve system reliability.
Work on the fiber feed system is still on hold.
System safety has been significantly enhanced with the completion of a wrap-around laser shield.
Finally, work has started on a laser auto-focus mechanism to help improve cut precision and speeds.