Skip to content Skip to navigation

Diode Laser

Incremental heating is accomplished using a fully automated, 75 W, 980 nanometer wave length diode laser system.  Tantalum or niobium-encapsulated samples are heated in two modes: (1) resting upon a stainless steel planchet; or (2) suspended on thermocouple wire extended from one of seven available ports of a sperical octagon.  The diameter of a collimated laser beam is adjusted to match the diameter of 1 mm Nb packets used for single crystals or 3mm diameter, Ta foil packets used for multi-grain aggregates.   The 30 cc laser chamber is rigidly mounted.  An actuated Zaber x-y stage positions the laser.  A 1.9" viewable sapphire window permits sufficiently widely separated samples to avoid beam overlap.  Trays designed to hold up to forty five 1 mm packets spaced at 4 mm can be loaded for an automated run.  Alternative trays hold 21 of the larger 3 mm packets spaced at 6mm.  Heating is monitored with a firewire IR Guppy CCD camera mounted on a Navitar camera and a 250-1650 C, 0.85 mm spot optical pyrometer mounted on an actuated Zaber mirror mount.  Laser output power is controlled either: (1) directly (e.g.., Current Mode) via internal current modulation in the OSTECH diode laser controller; or (2) via external modulation (e.g., PID mode) based upon thermocouple feedback or optical pyrometer response.  Temperature calibration is performed using the same procedures used to heat unknown samples and is based upon the melting point of Al foil and the Arrhenius behavior of kalsilite glass.  For diffusion measurements, reproducible sample heating is ensured by using routines to center the sample beneath the laser beam and the optical pyrometer upon the sample.