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OSE Ph.D. & M.S. Defenses

OSE Ph.D. Candidate - Capt. Shawn Hackett

Defense Date and Time: Thursday, November 3, 2016 from 10:30 AM to 12:00 PM
Location: Room 190, Physics & Astronomy Building

Dissertation Title:
"High Power Optically Pumped Semiconductor Disk Lasers for Sodium Guidestar Applications"

Committee Members:

  • Professor Mansoor Sheik-Bahae (Chair)
  • Professor Majeed Hayat - ECE
  • Professor McGraw - PHYC
  • Dr. Robert Johnson - AFRL

Optically Pumped Semiconductor Disk Lasers (OPSLs) are shown to provide a much more compact and less expensive source for illumination of the sodium layer of the mesosphere for use as a sodium guidestar via single and two photon excitation schemes.

OSE Ph.D. Candidate - Mr. Ruichao Zhu

Defense Date and Time: Tuesday, October 25, 2016, 10:00 AM to 11:30 AM
Room 146, Center for High Technology Materials

Dissertation Title:
"Scatterometry at 50 nm Half Pitch Features"

Dissertation Committee Members:

  • Dr. Steve Brueck (Chair)
  • Dr. Mansoor Sheik-Bahae (PHYC)
  • Dr. P. R. Schunk (Advanced Materials Laboratory, Sandia National Laboratories)
  • Dr. Francesca Cavallo (ECE)

Metrology technologies are the essential adjunct to Semiconductor manufacturing. An optical metrology, can provide a real-time, high throughput, non-contact, non-destructive accurate and flexible measurement, which no other technologies can provide. Scatterometry, as an optical metrology, was chosen to measure a 50 nm half pitch feature structures for both metallic grating sample and resist grating sample. Our results show that even for a laser wavelength ten times larger than the sample pitch, scatterometry can still provide enough characteristic structure information. A limitation study for both metallic and resist grating shows the fundamental limitation of scatterometry for different materials and structures based on current noise levels. We have demonstrated that scatterometry have a potential capability to measure a 10 nm feature size with a 405 nm laser.

Ph.D. Candidate - Mr. Zhou Yang

Dissertation Date and Time: Monday, October 17, 2016, 1:00 PM - 3:00 PM
Location: Room 1131, Physics and Astronomy Building

Dissertation Title:
"Novel concepts in semiconductor disk lasers"

Dissertation Committee Members:

  • Prof. Mansoor Sheik-Bahae - Chair
  • Prof. Arash Mafi
  • Prof. Daniel Feezell
  • Dr. Jeffrey Cederberg (currently at MIT Lincoln Lab)

Optically-pumped semiconductor disk lasers (SDLs) have received much attention in recent years for myriad of applications requiring intracavity access, good beam quality, wavelength versatility, and high output powers. The traditional scheme of these lasers feature a semiconductor distributed Bragg reflector (DBR) integrated with the active region, together forming an active mirror in an external free-space cavity. The active mirror component is fabricated by either epitaxial growth or post-growth processing. This places certain restrictions on SDL design, as material system choices become limited. It further hinders laser performance with regard to its thermal management and laser bandwidth (tuning range).

This dissertation is concerned with developing SDL’s without the integrated semiconductor DBR in order to mitigate the aforementioned restrictions. We exploit epitaxial lift-off and van der Waals bonding technique to investigate novel DBR-free SDL geometries. Active regions are directly bonded onto various destination substrates, such as right angle prisms forming a total internal reflection (TIR) geometry or optical windows in a transmission arrangement. A quasi-continuous operation is demonstrated using TIR geometry while schemes for continuous-wave operation are proposed in standing wave as well as various monolithic ring cavities. We demonstrate a standing wave monolithic SDL cavity, and analyze its performance.

With the transmission geometry, multi-Watt CW operation is achieved by employing single-crystal CVD diamond windows as heatspreaders: 2 W output power is obtained at 1.15 µm, and more than 6 W is collected at 1 µm. Numerical thermal analysis results suggest that DBR-free SDLs outperform traditional SDLs in thermal management when employing two diamond heatspreaders sandwiching the active region. Additionally, significantly broader wavelength tuning range (80 nm) is demonstrated compared with typical SDLs, in agreement well with our extended integrated modal-gain model. Implications of such bandwidth enhancement for modelocking operation and ultrashort pulse generation is presented.

Finally, we propose a novel gain-embedded meta-mirror (GEMM) concept based on the subwavelength grating structures. Our theoretical analysis show that an SDL constructed based on this concept offers superior thermal management capability with promising potentials for high-power scaling.