The SPIE Digital Library supporting services are currently being upgraded. During this process, which will take several hours, some services will be unavailable.
Users accessing the SPIE Digital Library through a subscribing institution’s network should have full access to that institution’s subscriptions. Users with personal subscriptions or nonsubscribers will be unable to download or purchase articles during this this time, except those that are open access.
SPIE regrets any inconvenience and appreciates your understanding.