Needle Optimization (Manual mode) allows you to insert thin layers manually. This may be useful when you solve complicated design problems.

The Needle Variation window displays the plot of a special perturbation function,  the P-function, that is used to determine where new layers should be inserted in the current design structure. The colors of the curves in the plot are coordinated with the colors assigned to the specific materials loaded in memory.  The following options are provided in the Manual mode:

Needle - allows you to manually determine where to insert a new layer in a design.  When this command is initiated a vertical cursor that can be moved with the mouse displayed in the Needle Variation window.  

Refinement - starts a refinement procedure after the  insertion of a needle.

 References:

1. Sh. Furman and A.V.Tikhonravov, "Basics of optics of multilayer systems", Editions Frontiers, Gif-sur Yvette, 1992, 242 p.
2. A. V. Tikhonravov, M. K. Trubetskov, and G. W. DeBell, "Optical coating design approaches based on the needle optimization technique," Appl. Opt. 46, 704-710 (2007).
3. A. V. Tikhonravov and M. K. Trubetskov, "Modern status and prospects of the development of methods of designing multilayer optical coatings," J. Opt. Technol. 74, 845-850 (2007).
4. A. Tikhonravov and M. Trubetskov, "Modern design tools and a new paradigm in optical coating design," Appl. Opt. 51, 7319-7332 (2012).
5. A. V. Tikhonravov, M. K. Trubetskov, and G. W. DeBell, "Application of the needle optimization technique to the design of optical coatings," Appl. Opt. 35, 5493-5508 (1996).