A laundry dryer has a casing accommodating therein a drying air circuit and operational devices for carrying out a drying treatment on laundry. A computer can associate messages with threads by storing a thread identifier identifying a thread and associating the thread ID with a message identifier of each known message that belongs to the thread. The gain material has an absorption approximately resonant with the pump source wavelength, and the dopant concentration is selected to maximize absorption strength for a given excitation. , half, of the tones are left unused facilitating SIR measurement.