Core Readings:
Ruins of Desert Cathay – Vol I, Chapter, XXXIV pp. 392 thru 402, Records from an Ancient Rubbish Heap https://archive.org/details/ruinsofdesertcat01stei/page/392
Lop Nur – Wikipedia 5 pages including extensive illustrations https://en.wikipedia.org/wiki/Lop_Nur
Recommended but not Required:
Video:
YouTube: The Silk Road I, 5 of 12 - In Search of the Kingdom of Lou-Lan https://www.youtube.com/watch?v=dPA9RDZ9X7M&index=6&list=PLILRQ_uVCaoOtZ6Q6egVvUyEMhbN7OG9y&t=816s
For Further Reading:
Han Emperor Wu-ti's Interest in Central Asia and Chang Chien's (Zhang Qian's) Expeditions http://silkroadfoundation.org/artl/wuti.shtml. 3 pages, including illustrations