<p>Laser ablation of aluminum, silicon, titanium, germanium, and indium antimonide at 1064 nm in ambient laboratory air with pulse durations ranging from 100 ps to 100 μs has been characterized with optical microscopy. Highly focused spots of 10 μm yields fluences of 0.004 to 25 kJ / cm<sup>2</sup> and irradiances spanning 4 × 10<sup>6</sup>-10<sup>14</sup> W / cm<sup>2</sup>. Single pulse hole depths range from 84 nm to 147 μm. A one-dimensional thermal model establishes a set of nondimensional variables for hole depth, fluence, and pulse duration. For pulse durations shorter than the radial diffusion time, the hole depth exceeds the thermal diffusion length by a factor of 1 to 30 for more than 90% of the data. For pulses longer than this critical time, transverse heat conduction losses dominate and holes as small as 10<sup> − 3</sup> times the thermal diffusion depth are produced. For all cases, the ablation efficiency, defined as atoms removed per incident photon, is 10<sup> − 2</sup> or less, and is inversely proportional to volume removed for pulse durations less than 100 ns. At high fluences, more than 10 to 100 times ablation threshold, explosive boiling is identified as the likely mass removal mechanism, and hole depth scales approximately as fluence to 0.3 to 0.4 power. The power-law exponent is inversely proportional to the shielding of the laser pulse by ejected material, and shielding is maximum at the 1-ns pulse duration and minimum near the 1-μs pulse duration for each material. Using the thermal scaling variables, the high-fluence behavior for each material becomes strikingly similar.</p>
ZnSe doped with Cr<sup>2+</sup> was analyzed by EDS, XPS and Micro-Raman spectroscopy techniques. EDS and XPS
analysis revealed that chromium concentration is more than 2% and there are additional impurities, Ga, Ti, and Ta.
EDS measurements did not reveal any variation in chromium concentration when a line scan was performed over a
200 μm distance. XPS analysis indicated that the sample surface is inhomogeneous. Photoluminescence was
acquired by exciting the sample with 325 nm laser beam. Photoluminescence revealed charge transfer bands.
Micro-Raman study revealed the LO, TO and 2TA modes at 252, 205 and 140 cm<sup>-1</sup>. Under 488 or 514.5 nm
excitation background luminescence was predominant due to excitation of Cr<sup>2+</sup> electrons into the conduction band.
However, 632.8 nm laser excitation revealed, strong Raman signals. Raman data were acquired by exciting the
sample on the grain boundary and inside the domain. The ratio of LO and TO peak intensities changed randomly
when data were acquired from different points on the grain boundary indicating the presence of random strain in the
material. When Raman data were acquired from different points on the sample surface for comparison, it revealed
that the LO mode was distorted as well as broadened whereas the TO mode intensity increased. This was due to the
presence of local modes induced by the sample inhomogeneity and the interaction of the holes with the LO mode.
We report the first demonstration of a gain-switched chromium-doped zinc selenide channel waveguide laser. The guided-wave structure was produced by ultrafast laser inscription and exhibited output pulse energies up to 12 μJ . The laser exhibited narrow spectral output with a linewidth less than 1 nm. The beam quality was measured to be M<sup>2</sup> ≤ 7 with a highly multimode output profile. The laser had a maximum slope efficiency of 9.8% and no deleterious thermal effects were observed up to an average pump power of 3.3 W .
Fe:ZnSe lasers have been pumped by several types of diode-pumped solid state laser, including Cr:Er:YSGG (2800 <i>nm</i>),<sup>1</sup> Cr:CdSe (2970 <i>nm</i>),<sup>2</sup> and Er:YAG (2698 <i>nm</i>,<sup>3</sup> 2936 <i>nm</i><sup>4</sup>). None of these sources has exceeded 1.5 <i>W</i> of true continuous-wave (CW) output power. In this work, we report demonstration of a CW Fe:ZnSe laser pumped by a 10 <i>W</i> Er:Y<sub>2</sub>O<sub>3</sub> laser emitting at 2740 <i>nm</i>,<sup>5</sup> which had not been previously attempted. The Er:Y<sub>2</sub>O<sub>3</sub> pump laser was characterized with respect to propagation losses, beam quality, mode size, and pointing stability. It was determined that the limit of output power from the Fe:ZnSe laser was limited by the output stability of the pump laser. The Fe:ZnSe laser operated with < 22% slope efficiency and 800 <i>mW</i> output power was achieved at approximately 4050 <i>nm</i>.
In this paper, we report on building and testing a Cr:ZnSe gain-switched amplifier pumped by a Q-switched Ho:YAG laser and seeded by a continuous wave (CW) tunable Cr:ZnSe laser. A 0.5%-doped, Brewster-cut Ho:YAG rod in an actively Q-switched, folded cavity produced 250 μJ pump pulses at 2.09 μm with pulse widths on the order of 400 ns. The seeded single-pass Cr:ZnSe amplifier exhibited output pulse energy as high as 3.8 μJ at 2.45 μm while pumped at a 10 kHz repetition rate. The gain-switched process showed a peak gain of 380 and an extraction efficiency of 1.5%. The system was tunable from 2160 nm to 2560 nm and had gain of 200 over a 400 nm range.
We have achieved ≥ 840 mW continuous-wave (CW) output power from iron-doped zinc selenide (Fe:ZnSe).1 The beam quality was measured to be M2 ≤ 1.2. The laser exhibited a slope efficiency of 47% with no thermal roll-off at maximum output power. Various dichroic mirrors and other spectral filters were inserted into the cavity to discretely tune the output of the laser from 3843 <i>nm</i> to 4337 <i>nm</i>. Demonstration of arbitrary discrete tuning shows that, in principle, Fe:ZnSe is capable of efficient continuously-tunable CW lasing over nearly 500 <i>nm</i> of bandwidth.
In this paper, we report record nanosecond output energies of gain-switched Cr:ZnSe lasers pumped by Q-switched
Cr:Tm:Ho:YAG (100 ns @ 2.096 μm) and Raman shifted Nd:YAG lasers (7 ns @ 1.906 μm). In these experiments we
used Brewster cut Cr:ZnSe gain elements with a chromium concentration of 8x10<sup>18</sup> cm<sup>-3</sup>. Under Cr:Tm:Ho:YAG
pumping, the first Cr:ZnSe laser demonstrated 3.1 mJ of output energy, 52% slope efficiency and 110 nm linewidth
centered at a wavelength of 2.47 μm. Maximum output energy of the second Cr:ZnSe laser reached 10.1 mJ under H<sub>2</sub> Raman shifted Nd:YAG laser pumping. The slope efficiency estimated from the input-output data was 47%.
We demonstrate a high-power (7.5 W) polycrystalline Cr<sup>2+</sup>:ZnSe CW laser system utilizing an astigmaticallycompensated
Kogelnik-configuration master oscillator and a normal-incidence slab power amplifier demonstrating over
2X gain. Experimental results are compared with an improved theoretical model of amplification in this type of system.
We used finite element software to model the time dependence of thermal lensing and temperature rise in a Cr<sup>2+</sup>-doped zinc selenide thin disk for pulsed pumping. Two cases, chopped cw and Q-switched pumping, were considered. The model agrees well with experimental results for the chopped pumping case but does not directly agree with Q-switched pumping because the time delay between absorption and heat transfer to the host material is not accounted for in our model.