This Ph.D. work is dedicated to advancements in burst-mode laser technology and their
applications in MHz-rate high-speed gas-phase environments. A comprehensive computational
model for simulating experimental burst-mode systems is discussed. Direct comparison of the
modeled results to the output of a constructed nanosecond (ns) burst-mode laser shows agreement
within a factor of 2 for output energy, the temporal domain skews positively in an appropriate
manner, and the spectral domain correctly remains unchanged. The modeled output of a
femtosecond (fs) burst-mode laser displays near perfect agreement with its hardware, generating
only a 1.7% deviation for output energy, an 11% deviation in spectral bandwidth, and a temporal
profile that correctly remains unchanged. The experimental ns to fs burst-mode lasers systems used
to compare with the aforementioned model are described in detail and demonstrated for use in
measurements of temperature, species, and velocity at high repetition rates.
In the ns regime, a compact-footprint (0.18 m2
) flashlamp-pumped, burst-mode Nd:YAGbased master-oscillator power-amplifier (MOPA) laser is developed with a fundamental 1064 nm
output of over 14 J per burst. This portable laser system uses a directly modulated diode laser seed
source to generate 10 ms duration arbitrary sequences of 500 kHz doublet or MHz singlet pulses
for flow-field velocity or species measurements, respectively.
In the fs regime, a flashlamp-pumped burst-mode laser system with high peak power and a
broad spectral bandwidth of >10 nm is constructed without the use of nonlinear compression
techniques. A mode-locked, 1064.6 nm fundamental-wavelength broadband master oscillator, a
fiber amplifier/pulse stretcher, and four Nd:glass power amplifiers are used to generate a sequence
of high-repetition-rate, transform-limited 234 fs pulses over a 1 ms burst duration at a 0.1 Hz burst
repetition rate. The generated peak powers are 1.24 GW at 100 kHz and 500 MW at 1 MHz with
M2∼1.5.
An adaptation of the fs burst-mode laser is used for femtosecond laser electronic excitation
tagging (FLEET) of nitrogen for tracking the velocity field in high-speed flows at kilohertz–
megahertz (kHz–MHz) repetition rates without the use of added tracers. The fs burst-mode laser
is used to produce 500 pulses per burst with pulses having a temporal separation as short as 1 µs,
an energy of 120 µJ, and a duration of 274 fs. This enables 2 orders of magnitude higher
measurement bandwidth over conventional kHz-rate FLEET velocimetry.
15
The fs burst-mode system was further improved to include a picosecond (ps) leg for hybrid
fs/ps rotational coherent anti-Stokes Raman scattering (RCARS) at MHz rates. Using a common
fs oscillator, the system simultaneously generates time synchronized 1061 nm, 274 fs and 1064
nm, 15.5 ps pulses with peak powers of 350 MW and 2.5 MW, respectively. The system is
demonstrated for two-beam fs/ps RCARS in N2 at 1 MHz with a signal-to-noise ratio of 176 at
room temperature. This repetition rate is an order of magnitude higher than previous CARS using
burst-mode ps laser systems and two to three orders of magnitude faster than previous continuously
pulsed fs or fs/ps laser systems.
As a continuation of the above advances in fs regime, a regenerative fs burst-mode laser is
discussed in detail with motivations, design layouts, and cavity physics laid out. Preliminary
construction of the system with a ns seed source is underway to assess the detailed system design
and evaluate the potential for optical damage due to Kerr lensing or other nonlinear effects. This
system and other potential follow-on research topics are discussed.
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/13261913 |
| Date | 16 December 2020 |
| Creators | Michael Smyser (9661982) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/Burst-Mode_Laser_Development_for_MHz-Rate_Diagnostics/13261913 |
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