Michael D. Thomas's scientific contributions
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Publications (20)
This paper introduces a sensitivity test for characterizing the laser damage behavior of a sample. A sensitivity test analyzes unbinned laser damage test data to estimate the damage probability curve. The means of estimation is by employing a parametric model of the probability of damage and identifying the parameters most likely to produce the obs...
This paper continues an investigation into the applicability of maximum likelihood methods to the
problem of laser damage threshold measurement. This year’s investigation applies maximum likelihood
methods to an archival set of data and compares two models of damage probability. The Type 1 model
has a defined threshold, below which the probability...
Laser damage measurements share similarities with testing of explosives,
namely the sample or sample site is damaged or modified during the
measurement and cannot be retested. An extensive literature exists for
techniques of measurement of the "all fire" and "no fire" levels for
explosives. These levels hold direct analogy to the "all damage" or 10...
Laser bulk damage thresholds were measured for both single-crystal YAG
and for diffusion-bonded YAG structures using 600 picosecond pulses at
1064 nm. The tested samples included 3-layer sandwich structures with
doped cores of various thicknesses. An undoped-YAG end cap was
diffusion-bonded on one end of each of the sandwiches. The 1064 nm laser
so...
UV antireflection coatings are a challenging coating for high power
laser applications as exemplified by the use of uncoated Brewster's
windows in laser cavities. In order to understand the current laser
resistance of UV AR coatings in the industrial and university sectors, a
double blind laser damage competition was performed. The coatings have a...
Replacing growing damage sites with benign, laser damage resistant features in multilayer dielectric films may enable large mirrors to be operated at significantly higher fluences. Laser damage resistant features have been created in high reflecting coatings on glass substrates using femtosecond laser machining. These prototype features have been d...
A laser damage competition was held at the 2008 Boulder Damage Symposium in order to determine the current status of thin film laser resistance within the private, academic, and government sectors. This damage competition allows a direct comparison of the current state-of-the-art of high laser resistance coatings since they are all tested using the...
Antireflection (AR) coatings typically damage at the interface between the substrate and coating. Therefore the substrate finishing technology can have an impact on the laser resistance of the coating. For this study, AR coatings were deposited on Yb:S-FAP [Yb3+:Sr5(PO4)3F] crystals that received a final polish by both conventional pitch lap finish...
The laser damage test for qualifying a coating run of anti-reflection coated optics consists of scanning a pulsed 1064 nm laser to illuminate approximately 2400 sites over a 1 cm x 1 cm area on a test sample. Scans are repeated at 3 J/cm2 increments until the fluence specification for the optic is reached. In the past, initiation of 1 or more damag...
When completed, the National Ignition Facility (NIF) will provide laser energies in the Mega-joule range. Successful pulse amplification to these extremely high levels requires that all small optics, found earlier in the beamline, have stringent surface and laser fluence requirements. In addition, they must operate reliably for 30 years constitutin...
The NIF injection laser system requires over 8000 precision optical components. Two special requirements for such optics are wavefront and laser damage threshold. Wavefront gradient is an important specification on the NIF ILS optics. The gradient affects the spot size and, in the second order, the contrast ratio of the laser beam. Wavefront errors...
Citations
... Secondly, coatings for the visible wavelength range have not been explored in previous competitions. [2][3][4] Indeed, the types of coatings, wavelengths, pulse lengths and laser sources employed in past surveys are summarized in Fig. 1 and reveal a glaring absence of data at 2ω. More details on specific topics can be found in Ref. 5. ...
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... Compared with samples obtained by dual ion beam sputtering coatings [36], aluminium silicate films obtained by PLD showed promising results. The obtained values, taking into account the uncertainty, are also comparable with other data from literature [37]. ...
... The top entry was an alumina silica coating deposited with ion beam sputtering (IBS). 9 Alumina and silica are also used extensively for excimer laser mirror coatings. [10][11][12][13] However, these coatings are fairly thin because they are used just in the ultraviolet (UV). ...
... The quality of films on optical components is a critical factor for high peak power laser system application due to the spectral performance, environmental stability, and service life. Al2O3 thin films grown with different deposition techniques have already found application in multilayer coatings for laser optics [13,14] and shown improved laser damage thresholds when incorporated with hafnia and silica multilayer mirrors [10]. However, there is still the potential to further optimize the laser damage threshold and film stresses to achieve even better laser mirror performance. ...
... Delamination is a manifestation of damage that causes issues in many different applications. In optical applications, delamination of functional coatings (for instance, antireflective coatings) represents an irreversible damage to optical equipment that may be provoked by (unintentional) exposure to high-energy density laser radiation [1,2]. In industrial, construction, and automotive applications, delamination of protective coatings [3,4] results in the underlying material being exposed to environmental influences that could favor corrosion. ...
... A number of strategies have been implemented to improve the laser-induced damage threshold of multilayer coatings and to extend their performance lifetime. These include eliminating or reducing coating defects [13,14], post-conditioning by gradually exposing coatings from low to high fluences [15], and replacing initiated sites with benign micro-machined features that are stable at or above the operating (or use) fluence [16,17]. Alternatively, adding an absentee overcoat (or protective capping layer) above the original HR mirror coatings has also been shown to improve the laser-damage resistance [18][19][20], the degree to which depends on the capping layer's thickness. ...
... [15,16]. However, unlike the deterministic damage induced by ultra-short laser pulses, damage in the nanosecond regime has obvious statistical behavior that is related to the initiation of precursor defects [18]. Therefore, the 1-on-1 test method with a small number of samplings was unable to evaluate the LIDT as well as the critical defects induced by the ns laser pulse effectively. ...
... In laser applications, SiO 2 and HfO 2 are preferred in the multilayer stack as low and high refractive index material, respectively. Besides low optical losses, low absorption in the UV range, HfO 2 exhibits a high laser-induced damage threshold compared to other high index materials [5][6][7]. ...
