In the report covering the last quarter of 1999, it was noted that the emphasis had been on improving the front end of the stacking code to make life easier for the TO's. During the first quarter of 2000, efforts have partially returned to improving stack quality.

In addition, a new version of the stacking code has been written for CCAS testing. This version allows stacking of any (small) number of mirrors anywhere on the primary mirror. The current version of this code allows stacking of any number smaller than 10.

Code has also been written which allows numerical modeling of CCAS stacks to determine how large stacking errors are, how much better we might do by reducing measurement error, whether the goal of EE(50) = 0.6 arcseconds is reachable and a number of other topics. View this technical report.

During the time covered by this report, stacking speed remained roughly constant. Measured from arrival at CCAS to departure from CCAS the median time is still about 10 minutes. The upper panel of Figure 1 shows this time as circles. Crosses show time away from the sky. It has decreased slightly and is now about 17 or 18 minutes. This slight reduction is due to the elimination of our former practice of taking images of the stack upon first arrival at CCAS.

The lower panel of Figure 1 shows the change in EE(50) and EE(80) over the last two years binned into approximately one month bins. The slight increase of EE(50) and EE(80) during the month of December and January is probably due to degraded hysteresis corrections and actuator failures due to cold weather. Figure 2 presents a histogram of EE(50) and EE(80) results during the first quarter of 2000.

We have instituted one change in the stacking procedure which has resulted in improvements to the stack quality. After stacking half of the mirror the second half of the mirror is stacked on top of the stack of first half mirrors. Quite often that first side stack is saturated. By switching to a lower intensity laser while stacking the second side we have found that we can achieve EE(50) values typically between 1.0 and 1.1.

Figure 1: Stacking time (upper panel) and quality (lower panel) over the past two years. In the upper panel, circles are time from arrival at CCAS to departure from CCAS and crosses are time away from the sky. In the lower panel, circles are EE(50) and crosses are EE(80).

Figure 2: Histogram of stack quality measurements during the months of Jan., Feb., Mar., 2000.