After a brief examination of known insulating laser crystals and the stimulated emission channels of their generating activator ions, this article reviews recent advances in the development of novel lasing crystals and ceramics, as well as inorganic and organic nonlinear-laser crystals for χ(3) and cascaded χ(3) ↔ χ(2) frequency converters Several new modern attractive technologies in the physics and techniques of crystalline lasers are also discussed

https://onlinelibrary.wiley.com/doi/pdf/10.1002/lpor.200710008

Laser crystals and ceramics: recent advances

A diode‐array side‐pumped Er, Yb: phosphate glass laser has been constructed. Pumped with two 970 nm, InGaAs strained‐layer diode arrays, a long pulse slope efficiency of 14% was obtained, with thresholds of 60 mJ input, a maximum output pulse energy of 20 mJ, and with output wavelengths at 1545±12 nm. When Q‐switched, the laser generated 0.3 mJ, 50 ns FWHM pulses at an output wavelength of 1533±1 nm. Visible upconversion emission in the laser rod was observed.

Diode array‐pumped Er, Yb: Phosphate glass laser

As a widely used semiconductor material, silicon has been extensively used in many areas, such as photodiode, photodetector, and photovoltaic devices. However, the high surface reflectance and large bandgap of traditional bulk silicon restrict the full use of the spectrum. To solve this problem, many methods have been developed. Among them, the surface nanostructured silicon, namely black silicon, is the most efficient and widely used. Due to its high absorption in the wide range from UV-visible to infrared, black silicon is very attractive for using as sensitive layer of photodiodes, photodetector, solar cells, field emission, luminescence, and other photoelectric devices. Intensive study has been performed to understand the enhanced absorption of black silicon as well as the response extended to infrared spectrum range. In this paper, the application of black silicon is systematically reviewed. The limitations and challenges of black silicon material are also discussed. This article will provide a meaningful introduction to black silicon and its unique properties.

/pdf/review-application-of-nanostructured-black-silicon-8c7rrnbp8y.pdf

Review Application of Nanostructured Black Silicon

Color marking of rough or smooth metal (Al, Cu, Ti) and semiconductor (Si) surfaces was realized via femtosecond laser fabrication of periodic surface nanorelief, representing one-dimensional diffraction gratings. Bright colors of the surface nanorelief, especially for longer electromagnetic wavelengths, were provided during marking through pre-determined variation of the laser incidence angle and the resulting change of the diffraction grating period. This coloration technique was demonstrated for the case of silicon and various metals to mark surfaces in any individual color with a controllable brightness level and almost without their accompanying chemical surface modification.

Femtosecond laser color marking of metal and semiconductor surfaces

Crystallographic and optical properties of NaLa(${\mathrm{MoO}}_{4}$${)}_{2}$ are presented. The positions of the Stark levels are reported for the [LS]J manifolds of ${\mathrm{Nd}}^{3+}$ and ${\mathrm{Er}}^{3+}$ up to the absorption edge in this host material. A least-squares fit to the data was performed to obtain the crystal-field parameters. For ${\mathrm{Nd}}^{3+}$ the following crystal-field parameters were obtained: ${\mathit{B}}_{20}$=519, ${\mathit{B}}_{40}$=-695, ${\mathit{B}}_{44}$=964, ${\mathit{B}}_{60}$=-190, and ${\mathit{B}}_{64}$=673+i384 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, with a root-mean-square (rms) deviation of 7.7 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. For ${\mathrm{Er}}^{3+}$ we obtained ${\mathit{B}}_{20}$=422, ${\mathit{B}}_{40}$=-507, ${\mathit{B}}_{44}$=839, ${\mathit{B}}_{60}$=-116, and ${\mathit{B}}_{64}$=409+i158 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, with a rms deviation of 4.8 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. Intensity calculations based on fits to the experimental data yield line-to-line and multiplet branching ratios. The results of this investigation indicate that ${\mathrm{Er}}^{3+}$:NaLa(${\mathrm{MoO}}_{4}$${)}_{2}$ and ${\mathrm{Nd}}^{3+}$:NaLa(${\mathrm{MoO}}_{4}$${)}_{2}$ show promise as diode-pumped laser materials.

NaLa(MoO4)2 as a laser host material

Nd:YAG (YAG) and Nd:Lu:YAG (LYAG) are investigated as high-efficiency laser materials utilizing a diode-array side-pump geometry. We demonstrate higher laser efficiencies than previously reported for transversely pumped YAG. A YAG rod yielded an optical slope efficiency of 47.7%, while a LYAG rod yielded an optical slope efficiency of 50.3%. Increased performance of these materials is attributed to higher pump absorption and lower losses.

Efficient diode-array-pumped Nd:YAG and Nd:Lu:YAG lasers.

Infrared transmittance and hemispherical-directional reflectance data from 2.5 to 25 μm on microstructured silicon surfaces have been measured, and spectral emissivity has been calculated for this wavelength range. Hemispherical-total emissivity is calculated for the samples and found to be 0.84 before a measurement-induced annealing and 0.65 after the measurement for the sulfur-doped sample. Secondary samples lack a measurement-induced anneal, and reasons for this discrepancy are presented. Emissivity numbers are plotted and compared with a silicon substrate, and Aeroglaze Z306 black paint. Use of microstructured silicon as a blackbody or microbolometer surface is modeled and presented, respectively.

Emissivity of microstructured silicon.

A miniature diode pumped Er,Yb:glass laser has been developed at the Night Vision and Electronic Sensors Directorate, U. S. Army CECOM (NVESD) for soldier applications. This device uses a single laser diode at 925 nm to end pump a 200µm x 3 mm volume of Er,Yb:glass gain media. A Co2+:MgAl2O4 passive Q-switch is used to produce 2 nanosecond pulses at a repetition rate from single shot to 20 Hertz. A nominal pulse energy of 100 microjoules is emitted, corresponds to a peak power of 50 kilowatts, which is sufficient for ranging to over 2 kilometer. The Eyesafe Microlaser was designed and demonstrated to operate over a wide temperature range without temperature control of the pump laser, a feature important for soldier applications. An desirable feature of Er,Yb:glass lasers is that they emit directly at 1.54 microns, which is important for eye safe operation and low cost fabrication.

Eyesafe erbium glass microlaser

A diode-end-pumped Tm:YLF laser, passively Q-switched (PQS) with a Cr:ZnS saturable absorber, generated 10 mJ, 29 ns-long pulses at 1.9 μm, corresponding to a peak power of 350kW. A PQS laser operated at a maximum pulse repetition frequency (PRF) of 1 kHz, generating an average power of 10 W. The demonstrated pulse energy and average power represent significant increases over previous results with PQS Tm-doped lasers, and the 10 mJ pulse energy is comparable to that of much more complex actively Q-switched versions of such lasers. Using a cadmium silicon phosphide (CSP) optical parametric oscillator (OPO), the laser output was converted to 3.5-4.2 μm mid-IR emission. The OPO exhibited an optical efficiency of 64%, and generated 6W of mid-IR power.

Passively Q-switched 10 mJ Tm:YLF laser with efficient OPO conversion to mid-IR

UV illumination of a lithium niobate Q-switch was demonstrated as an effective means to eliminate a loss in hold-off and associated prelasing that occurs under cold temperature operation of Q-switched lasers. This degradation occurs due to the pyroelectric effect, where an accumulation of charge on crystal faces results in a reduction in the Q-switch hold-off and a spatially variable loss of the Q-switch in its high-transmission state, both resulting in lowering of the maximum Q-switched pulse energy. With UV illumination, the resulting creation of photo-generated carriers was shown to be effective in eliminating both of these effects. A Q-switched Nd:YAG laser utilizing UV-illuminated LiNbO(3) was shown to operate under cold temperatures without prelasing or spatially variable loss.

Influence of UV illumination on the cold temperature operation of a LiNbO(3) Q-switched Nd:YAG laser.

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