We have a great deal of experience in designing and assembling laser systems. We started with solid-state lasers, back when diode-pumping was just beginning. (The first lasers we worked on used flashlamps to pump the laser rods.) We have developed laser sources for military, other government, and commercial purposes, for use in chemical analysis, long-range sensing, and target illumination. We are acknowledge experts in laser modeling, in particular rate equation analysis. Some of our laser-based publications are:

1. Kurtz, R.M. “How Lasers Are Like Wolves: A Deep Dive into Laser Performance Analysis, Rate Equations, and Ion-Ion Interactions.” Presented at IEEE SoCal Tech Talk. Online: 2021.
         Over the past 60 years, lasers have moved from a laboratory curiosity to useful items in everyday life. About five years after first realizing the laser, Ted Maiman referred to it as “a solution in search of a problem;” a 2006 documentary about the laser was named after this quote. Today, lasers are found in pointers, replacing a long stick; in CD, DVD, and Blu-Ray players; in cars, used for rangefinding; in telecommunication systems; and with a wide variety of scientific and military application. This growth in the capability of the laser has occurred partly due to improvements in technology and materials, and partly through better understanding of the transfer of energy within the laser material. When specific applications appear, it may be possible to design a laser to fit the need.
         Of course, if you want a laser for a particular use, it helps if you can predict and analyze its performance. A key method of doing so is the use of rate equations, first-order differential equations that tie together the rate of energy transfer within the laser material. These simple equations can be used to design and analyze a wide variety of laser capabilities – and can also be used to describe other systems that have related change rates. This talk will concentrate on the laser applications.
   There are many active media for lasers. For example, ion lasers (such as Ar+, Kr+, and HeNe) use ionized gases; the HeNe includes energy transfer among the He+ and Ne+ ions. If ions are added to solid materials, such as Nd3+ replacing a portion of the Y3+ in Nd:YAG, the laser is called solid-state, and can be more compact and more efficient than the ion gas lasers. Other laser forms include semiconductor (or diode) lasers, which use the emission of light at an electrical p-n junction to produce a laser beam; chemical lasers, which generate energy by producing chemicals that are already in an excited state; non-ionized gas lasers, which use vibrational and rotational modes to produce the beam; and enough related methods that an entire talk would be needed just to list and describe them.
         This talk concentrated on an introduction to rate equations and their application to laser performance analysis. Starting from the simplest possible system, we added more complexity and more energy transitions, including methods for optimizing the laser output as desired for various applications. We disucssed what happens when additional active materials are added to a laser, which can result in ion-ion interactions.
         We will even brought up how lasers are like wolves!
2. Gulses, A.A.; Rai, S.; Padiyar, J., et al. “Laser Beam Shaping with Computer-Generated Holograms for Fiducial Markings.” In: Dudley, A.; Laskin, A.V., editors. Laser Beam Shaping XIX. San Diego, California: SPIE; 11107, 2019. p. 1110716.
         The laser marking method has obvious advantages over other available marking methods in speed, accuracy, and flexibility. Mask marking and beam deflection marking are typical methods, each having advantages and disadvantages. In the former, an opaque mask is directly imaged to create the desired mark. This method is practical and relatively fast, but most of the marking energy is blocked, losing efficiency. Additionally, this method requires a precise and bulky lens system. In the latter method, the focused beam is steered onto the sample, writing point by point. This technique has higher flexibility between marks, but it is slow, requires micro-movements, and accurate micro-motion parts are very expensive.
         We propose an innovative, holographic approach in laser marking. In the new system, a holographic projection system based on a digitally designed computer-generated hologram (CGH) is employed. This specially designed, fully transparent, phase only CGH modulates the high-power writing beam to create any desired image in the far field, where the beam etches a permanent mark of that image onto the designated silicon wafer substrate. Holographic marking combines the advantages of mask and beam deflection marking methods, such as high speed and stationary operation with minimal power loss, in a relatively simple and inexpensive setup. Also, since the holographic projection maintains its image quality after a certain distance, the setup is less prone to spatial alignment errors. We believe that the proposed technique will make significant contributions in the field of laser marking.
3. Gulses, A.A.; Kurtz, R.M.; Islas, G.; Anisimov, I. “Lasers with Intra-Cavity Phase Elements.” In: Glebov, A.L.; Leisher, P.O., editors. High Power/Energy Laser Components and Packaging IV. San Francisco, California: SPIE; 10513, 2018. p. 1051342.
         Conventional laser resonators yield multimodal output, especially at high powers and short cavity lengths. Since high-order modes exhibit large divergence, it is desirable to suppress them to improve laser quality. Traditionally, such modal discriminations can be achieved by simple apertures that provide absorptive loss for large diameter modes, while allowing the lower orders, such as the fundamental Gaussian, to pass through. However, modal discrimination may not be sufficient for short-cavity lasers, resulting in multimodal operation as well as power loss and overheating in the absorptive part of the aperture.
         In research to improve laser mode control with minimal energy loss, systematic experiments have been executed using phase-only elements. These were composed of an intra-cavity step function and a diffractive out-coupler made of a computer-generated hologram. The platform was a 15-cm long solid-state laser that employs a neodymium-doped yttrium orthovanadate crystal rod, producing 1064 nm multimodal laser output. The intra-cavity phase elements (PEs) were shown to be highly effective in obtaining beams with reduced M-squared values and increased output powers, yielding improved values of radiance. The utilization of more sophisticated diffractive elements is promising for more difficult laser systems.
4. Kurtz, R.M.; Pradhan, R.D.; Tun, N., et al. “Mutual Injection Locking: A New Architecture for High-Power Solid-State Laser Arrays.” IEEE J Selec Top Quantum Elec. 11(3): 578-585; 2005. doi:10.1109/JSTQE.2005.850240.
         In this paper, bidirectional (mutual) injection locking is demonstrated with solid-state lasers, producing significant improvements over traditional single-direction injection locking. Each laser element shares part of its output with other elements in bidirectional locking, distinct from single-direction (traditional) injection locking where one master laser provides the locking signal for a number of slaves. In a phase-locked array, the individual laser outputs add coherently, and the brightness of the entire array scales with the square of the number of elements, as if the active material diameter were increasing. Benefits of bidirectional locking, when compared to traditional injection locking, include reduced laser threshold, better output beam quality, and improved scaling capability. Experiments using two Nd:YVO4 lasers confirmed that mutual injection locking reduced lasing threshold by The injection-locking effects began with 0.03% coupling between lasers and full-phase locking for coupling exceeding 0.5%. The 0.5% requirement for full-phase locking is significantly lower than the requirement for traditional injection locking. The large coupling requirement limits traditional injection-locked arrays to fewer than 20 elements, whereas mutually injection-locked arrays have no such limit. Mutual injection locking of an array of lasers can lead to a new architecture for high-power laser systems.
5. Kurtz, R.; Pradhan, R.D.; Aye, T.M., et al. “Mutual Injection Locking of Solid-State Lasers.” In: Langford, N., editor. CLEO. San Francisco, California: Optical Society of America, 2004. p. CTuCC7.
         Mutual injection locking of solid-state lasers provides significant improvements over traditional, single-direction injection locking. While both methods reduce lasing threshold and improve beam quality, mutual injection locking overcomes the traditional method’s limits.
6. Kurtz, R.M.; Pradhan, R.D.; Aye, T.M., et al. “Injection Locking Efficiency of Two Independent Lasers.” Laser Systems Technology. Orlando, FL: SPIE; 5413, 2004. p. 41-49.
      Bidirectional (mutual) injection locking was demonstrated with solid-state lasers, producing significant improvements over traditional single-direction injection locking. Each laser element shares part of its output with other elements in bidirectional locking, distinct from single-direction (traditional) injection locking where one master laser provides the locking signal for a number of slaves. In a phase-locked array, the individual laser outputs add coherently, and the brightness of the entire array scales with the square of the number of elements, as if the active material diameter were increasing. Benefits of bidirectional locking, when compared to traditional injection locking, include reduced laser threshold, better output beam quality, and improved scaling capability. Experiments using two Nd:YVO4 lasers confirmed that mutual injection locking reduced lasing threshold by a factor of at least two and increased the output beam quality significantly. The injection locking effects began with 0.03% coupling between lasers and full-phase locking for coupling exceeding 0.5%. The 0.5% requirement for full phase-locking limits traditional injection-locked arrays to fewer than 100 elements, while mutually injection-locked arrays have no such limit. Mutual injection locking of an array of lasers can lead to a new architecture for high-power laser systems.
7. Bass, M.; Shi, W.Q.; Kurtz, R., et al. “Operation of the High Dopant Density Er:YAG at 2.94 µm.” In: Budgor, A.B.; Esterowitz, L.; DeShazer, L.G., editors. Vol. 52, Tunable Solid-State Lasers II. New York: Springer-Verlag; 1986. p. 300-305.
    
8. Kurtz, R.M. “Determination of the Er3+ to Ho3+ Energy Transfer Coefficient in (Er, Ho):YAG.” In: Dubinskii, M., editor. Solid State and Diode Laser Technology Review. Los Angeles, California: Directed Energy Professional Society, 2005. p. SS1-1.
         The coefficient describing energy transfer from the first excited level of trivalent erbium to the first excited level of trivalent holmium in YAG was obtained from measurement of the relevant material parameters. The value of this coefficient is necessary for estimating the improvement in Er:YAG and/or Ho:YAG lasing when the two ions are co-doped in the same crystal. This coefficient determines the depopulation efficiency of the lower level of the erbium 3-μm transition and the sensitization of the upper level of the 2-μm transition in holmium. Our technique for measuring the energy transfer coefficient, by fluorescence decay measurements in conjunction with computer simulations of the decay and rate equation modeling, resulted in a value of 4.33x10^-19 cm^3s^-1, implying that the erbium --> holmium energy transfer is strong enough to improve the room-temperature holmium 2-μm laser.
9. Shi, W.Q.; Kurtz, R.; Machan, J., et al. “Simultaneous, Multiple Wavelength Lasing of (Er, Nd):Y3Al5O12.” Appl Phys Lett. 51(16): 1218-1220; 1987 Oct 19. doi:10.1063/1.98735.
         Simultaneous lasing of both Er3+ and Nd3+ ions in yttrium aluminum garnet is reported. The crystal was doped with 15% Er3+ and 1% Nd3+ ions. The Er3+ ions lased at 2.94 µm and the Nd3+ ions in a broad band from 1.01 to 1.15 µm with a strong peak at 1.064 µm. Significant ion-ion interaction is suggested by the drastically altered fluorescent lifetimes and unusual laser properties.
   
10. Machan, J.; Kurtz, R.; Bass, M., et al. “Simultaneous, Multiple Wavelength Lasing of (Ho, Nd):Y3Al5O12.” Appl Phys Lett. 51(17): 1313-1315; 1987 Oct 26. doi:10.1063/1.98713.
          Simultaneous lasing of both Ho3+ and Nd3+ ions in the same crystal of yttrium aluminum garnet (YAG) is reported. The crystal was doped with 10% Ho3+ and 1% Nd3+ ions. Lasing occurred at 2.940 and 3.011 due to Ho3+ ion transitions and at 1.064 µm due to a Nd3+ transition. Appropriate mirrors produced simultaneous lasing at 1.064 and 1.339 µm due to Nd3+ ion transitions. The fluorescent lifetimes of both the Nd3+ 4F3/2 and Ho3+ 5I7 states were significantly lower in the doubly-doped material than in Nd:YAG and Ho:YAG. This indicates very strong ion-ion interactions in the (Ho, Nd):YAG crystal.
11. Machan, J.; Kurtz, R.; Bass, M., et al. “The (Holmium, Neodymium):Yttrium Aluminum Garnet Multiple Wavelength Solid-State Laser.” Tunable Solid-State Lasers. Hilton Head, North Carolina: Optical Society of America; 3, 1987.
     
12. Kurtz, R.; Fathe, L.; Machan, J.; Birnbaum, M. “Multiple-Wavelength Lasing of (Er, Ho):YAG.” In: Jenssen, H.P.; Shand, M.L., editors. Advanced Solid State Lasers. Salt Lake City, Utah: Optical Society of America; 5, 1989. p. 175-178.
          We tested a solid state laser material, YAG doped with 30% (at.) Er3+ ions and 1.5% (at.) Ho3+ ions. The laser levels in both Er3+ and Ho3+ demonstrated altered lifetimes when compared to equivalently-doped Er:YAG and Ho:YAG, indicating moderate interactions between the Er3+ and Ho 3+ ions. When we lased (Er, Ho):YAG, we observed output at three wavelengths: approximately 2.939, 2.936, and 2.796 µm. The first two of these lased simultaneously, while the third appeared later in the same pump pulse. This lasing blueshift may be explained by excited-state absorption (ESA) in the Ho3+ ions.
13. Kurtz, R.; Fathe, L.; Birnbaum, M. “New Laser Lines of Erbium in Yttrium Aluminum Garnet.” In: Jenssen, H.P.; Dubé, G., editors. Advanced Solid State Lasers. Salt Lake City, Utah: Optical Society of America; 6, 1990. p. 247-250.
          We studied the lasing and spectroscopic properties of erbium in yttrium aluminum garnet, both as a single impurity and when codoped with neodymium or holmium. In all cases, we observed lasing at 2.936 and 2.939 µm; when erbium was codoped with holmium, we also observed lasing at 2.795 and 2.766 µm. (This is in contrast to (Er, Nd):YAlO3, which lased on only one line, 2.73 µm.) By determining the energy-level splitting implied by the four observed laser lines, and combining this with transmission spectroscopy, we were able to assign unambiguous values to the Stark sublevels of the three lowest energy levels of Er3+ in YAG at room temperature.
14. Kurtz, R. Spectroscopic and 3-Micron Lasing Properties of Erbium-Doped Yttrium Aluminum Garnet and the Effects of Holmium Co-Doping [Ph.D. Dissertation]. [Los Angeles, California]: University of Southern California; 1991. 100 p.
       The spectroscopy and 3-μm lasing behavior of Er:YAG are studied. Er:YAG is shown to lase on two distinct lines near 2.94 µm, specifically 2.9393 and 2.9362 µm. These two laser lines operate simultaneously. Although both begin in level A2 (the second lowest energy Stark sublevel of the 4111/2 level), the 2.9362-μm line terminates at level Y6 and the 2.9393-μrn line at level Y7 (Y7 and Y6 are the highest and second highest energy Stark sublevels, respectively, of the 4113/2 level). These wavelengths imply that the Y6 level, whose energy was previously unknown, has an energy of 6873.8 cm-1.
       The effects of adding Ho3+ ions to Er:YAG is also reported. Energy is transferred from the 4113/2 level of Er3+ to the 517 level of Ho3+. As reported in this dissertation, the
    value of the coefficient describing this energy transfer is WEH = 9.5±1.0 X 10-20 cm3/s (note that further analysis refined this value to 4.33 X 10-19 cm3/s). This value suggests that the Er3+-->Ho3+ energy transfer is not strong enough to unblock the Er:YAG 3-μm transition, but is strong enough to unblock the Er:YLF 3-μm transition. The energy transfer also suggests diode-pumping Er3+ ions, which then transfer their energy to the Ho3+ions, creating an efficient, diode-pumped 2-µm Ho3+laser.
       Multiple wavelength lasing of (30% Er, 1.5% Ho):YAG is described. In addition to the two wavelengths seen in Er:YAG, (Er, Ho):YAG lases at 2.796 and 2.766 μm during the same pump pulse as the 2.936- and 2.939-μm lines. Both these transitions are attributed to the Er3+ ions. The 3-μm lasing is shown to have a lower gain than the lasing near 2.8 μm, but atmospheric losses at 2.8 μm are sufficient to prevent lasing at these wavelengths. The 2.8-μm lines are seen in (Er, Ho):YAG after the 3-μm lines have self-terminated due to excited-state absorption in the Ho3+.
15. Yang, Y.; Pradhan, R.D.; Kurtz, R.M., et al. “Portable LIBS and Raman Spectroscopy Standoff Chemical Analysis System.” Presented at Detection and Remediation Technologies for Mines and Minelike Targets XII. Orlando, Florida: 2007.
     
16. Kurtz, R. “Increasing Your Laser System's Lifetime.” The Fabricator. 22: 34-49; 1992.
       When using lasers in an industrial setting, there are many sources of unbudgeted costs. Among these costs are costs of replacing lenses and reflectors damaged in use, the costs of remachining parts which were incorrectly machined due to alignment or laser quality problems, and down time for unexpected repairs.
       Although none of the sources of unbudgeted costs can be eliminated, many can be ameliorated by a properly implemented routine maintenance program. Such a program prevents many problems by anticipating and eliminating the causes, and reduces the damage of others by detecting blemishes before they turn into disasters. Those companies which have implemented effective routine maintenance programs have mean times between failure of their laser machining systems several times longer, and mean times to repair these systems several times shorter, than companies that have no such program.
       This paper presents an example of a routine maintenance program. This program does take some time to implement, probably about five to six hours per month, but this time is likely to be less than the down time prevented by its implementation. When one also recalls the cost reduction due to avoidance of unexpected replacements and remachining, it becomes obvious that implementing a good maintenance program pays for itself in increased efficiency and reduced down time.
17. Gulses, A.; Kurtz, R., inventors; Luminit, LLC assignee. Laser Diode Enhancement Device. Patent US010090639B1. 2018 October 2.
          The subject invention includes a semiconductor laser with the laser having a DBR mirror on a substrate, a quantum well on the DBR mirror, and an interior CGH with a back propagated output for emitting a large sized Gaussian and encircling high energy.  The DBR mirror has a plurality of GaAs/AlGaAs layers, while the quantum well is composed of AlGaAs/InGaAs.  The CGH is composed of AlGaAs.
18. Kurtz, R.; Gulses, A., inventors; Luminit, LLC assignee. Spectrally Pure Short-Pulse Laser. Patent US010281391B2. 2019 May 7. 7 p.
          A laser system containing an etalon to reduce the spectral bandwidth and for tuning, with cavity dumping to generate the short pulses is described. The resulting system is stable and not overly complicated. The combination of cavity dumping with an intracavity etalon enables the invention to produce a string of short pulses, each of which has a very narrow spectral bandwidth. Tuning the wavelength over a spectral range that is very small, but much larger than the laser’s spectral bandwidth, enables the invention to use dual-wavelength lidar, DIAL, differential spectroscopy, or a combination of these methods to measure the concentration of the desired chemicals with excellent accuracy.