We describe a compact mid-IR source utilizing an intracavity, non-critically phase matched potassium titanyle arsenate (KTA) optical parametric oscillator (OPO) placed inside a passively Q-switched (PQS), 1.064 µm Nd:YAG laser resonator. A 45-degree dichroic beam splitter was employed to split the 1.064 µm resonator leg from the 1.5 μm/3.5 μm KTA OPO cavity that was singly resonant for the 1.5 μm signal. The 20 mm long KTA crystal was placed in the shared-path section of both cavities, with the KTA OPO output coupler partially reflective at 1.5 μm, and highly transmitting at 3.5 μm. With the Nd:YAG pumped by a 3-λ 12-bar diode stack at 5 Hz PRF, the KTA OPO generated 23.1 mJ signal pulses at 1.5 μm and 9.8 mJ idler pulses at 3.5 μm. To further increase the 3.5 μm energy, a cadmium silicon phosphide (CSP) optical parametric amplifier (OPA), phase matched for 1.5 μm-pumped amplification of 3.5 μm radiation, was placed immediately after the KTA OPO output coupler. A maximum 3.5 μm pulse energy of 13.2 mJ was measured after the OPA, with an additional 4.2 mJ generated at 2.8 μm. The 3.5 μm pulses had a measured temporal duration (FWHM) of 27 ns, corresponding to a peak-power of approximately 490 kW. This paper will detail the Nd:YAG pumped intracavity KTA OPO / CSP OPA and optimization of its performance as a pulsed midIR source.
A 1908 nm Tm:YLF laser, passively Q-switched (PQS) using a Cr:ZnS saturable absorber, is shown to generate significantly higher pulse energy and peak power than previously reported. Using a compact 13 cm-long, plano-concave resonator cavity, the end-pumped Tm:YLF laser generated 15.6 mJ, 26ns FWHM pulses, corresponding to a peak power of 600 kW, with a 0.5kHz PRF, and 7.8W average power. A 10 cm-long laser generated 10 mJ, 20 ns long pulses, with a 1 kHz PRF and 10 W average power. A laser utilizing the shortest, 4.5 cm-long cavity, generated 7 ns pulses with a pulse energy of 3.7mJ. All of the laser configurations incorporated a Volume Bragg Grating (VBG) high reflectivity cavity mirror to lock the laser wavelength and polarization. To minimize the energy fluence at Cr:ZnS saturable absorbers (To=88.6% and To=91.6%), they were placed near the concave output coupler where that laser mode field area of the plano-concave laser resonator was at its maximum.
We demonstrate operation of a compact, passively Q-switched Yb:YAG laser producing 10W average power at 1030nm in an 8.5kHz train of 1.2mJ, 1.6ns pulses. The laser is cw end-pumped with a fiber-coupled wavelength-stabilized 940nm diode. The pump light from the 105m diameter (0.1 NA) pigtail is collimated using a short focal length lens and directed into a 3mm long, 1mm thick 10 at.% Yb:YAG crystal. The saturable absorber is a Cr4+:YAG crystal with 76% unsaturated transmission. The laser’s slope efficiency is 52% and the optical-to-optical conversion efficiency is 33% at a pump power of 30W.
We describe a compact mid-IR source utilizing an intracavity, non-critically phase matched potassium titanyle arsenate (KTA) optical parametric oscillator (OPO) placed inside a passively Q-switched (PQS), 1.06μm Nd:YAG laser resonator. The 20mm long KTA intracavity OPO was singly resonant, with the output coupler coated for partial reflectivity of 60% at the 1.5μm signal emission and for high transmission at the 3.5μm idler wavelength. With the Nd:YAG pumped by a 3-λ 12-bar diode stack at 5Hz PRF, the OPO generated a maximum 20mJ signal pulse at 1.5μm and 8.8mJ idler pulse at 3.5μm. A cadmium silicon phosphide optical parametric amplifier (OPA), phase matched for 1.5μm-pumped amplification of the 3.5μm OPO idler, was placed in the near field of the intracavity OPO to further increase the mid-IR pulse energy. A maximum 3.5μm pulse energy of 12.1mJ was measured after the OPA, with an additional 4.0mJ measured at 2.8μm. The 3.5μm pulses had a temporal duration of 20ns, corresponding to a peak-power of 605kW. This paper will detail the Nd:YAG pumped intracavity KTA OPO/CSP OPA and optimization of its performance for maximizing the mid-IR pulse energy.
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.
We characterize several configurations of compact, Q-switched, 1.5 um lasers based on Er/Yb doped glass. Such lasers are required for eye-safe laser range-finders (LRF), laser markers, and illuminators for 3D and gated imaging. While 1-3 Hz pulse repetition frequency (PRF) is adequate for LRFs, the other applications require much higher PRFs to achieve near-real-time image refresh rates. Lasers described here utilize Er/Yb glass active elements, side-pumped by a 940 nm laser diode bar, or end-pumped by a fiber-coupled laser diode, and made use of active or passive Q-switching (PQS) techniques. Active Qswitching is implemented with resonant scanning mirror, and PQS utilizes Co:Spinel saturable absorbers. Q-switched pulse energies of 5mJ and 3mJ are achieved with side-pumping and end-pumping, respectively. An optical efficiency of over 3.7%, the highest to our knowledge for a PQS Er/Yb glass laser, is measured for the end-pumped implementation. When configured to generate 1mJ, the endpumped PQS laser operates over a 2-25 Hz PRF range, with nearly constant pulse energy and optical efficiency. Features and advantages of the various laser configurations are compared.
We describe mid-IR sources utilizing a CSP Optical Parametric Oscillator (OPO) directly pumped by a high efficiency 1.94 μm Tm:YAP Q-switched laser. The OPOs, constructed using the latest generation CSP crystals with low 1.94 μm absorption, were operated at near-degeneracy with mid-IR output in the 3.6-4.2 μm range. Compact Q-switched Tm:YAP lasers, implemented using both a Cr:ZnS saturable absorber Q-switch or a mechanical Q-switching (MQS) technique, were constructed with the Q-switching method’s impact on OPO performance evaluated. Resonant effects were observed for MQS that were absent in the passively Qswitched (PQS) experiment. It was determined that optimizing the OPO resonator length, relative to the cavity length of the Tm:YAP laser, maximized the OPO conversion efficiency. An optimized OPO, pumped at an incident 1.94μm MQS laser power of 7.6W, generated an average mid-IR power of 4.6 W, corresponding to an optical conversion efficiency of 60%, and an overall optical efficiency for mid-IR generation of 21% relative to diode power incident on the Tm:YAP.
We describe mid-IR sources utilizing ZGP and CSP Optical Parametric Oscillators (OPO) directly pumped by high efficiency 1.94 μm Tm:YAP Q-switched lasers. Compact Q-switched Tm:YAP lasers, implemented using Cr:ZnS saturable absorbers, generated 29 kW peak power pulses and an average power of 4W. The OPOs, constructed using the latest generation ZGP and CSP crystals with low 1.94 μm absorption, were operated at near-degeneracy with mid-IR output in the 3.6-4.2 μm range. Various doubly-resonant OPO configurations were evaluated, including single-pass pump pass and double-pass pumping. Maximum mid-IR powers of 2.3 W and 2.5 W and optical conversion efficiencies of 58% and 64% were measured for ZGP and CSP double-pass pump OPOs, respectively.
Highly efficient, diode pumped Tm:YAP lasers generating emission in the 1.85-1.94 μm range are demonstrated and characterized. Laser optical efficiencies of 51% and 45%, and electrical efficiencies of 31% and 25% are achieved under CW and Q-switched operation, respectively. Laser performance was characterized for maximum average powers up to 20W with various cavity configurations, all using an intra-cavity lens to compensate for thermal lensing in the Tm:YAP crystal. Q-switched lasers incorportating a Cr:ZnS saturable absorber (SA), resonant mechanical mirror scanner, or acousto-optic modulator were characterized. To enable higher average output powers, measurements of the thermal lens were conducted for the Tm:YAP crystal as a function of pump power and were compared to values predicted by a finiteelement- analysis (FEA) thermal-optical model of the Tm:YAP crystal. A resonator model is developed to incorporate this calculated thermal lens and its effect on laser performance. This paper will address approaches for improving the performance of Tm:YAP lasers, and means for achieving increased average output powers while maintaining high optical efficiency for both SA and mechanical Q-switching.
We describe generation of near-infrared (944nm, 970nm), blue (472nm, 485nm), and UV (236 nm) light by frequency up-conversion of 2 μm output of a compact and efficient passively Q-switched Tm:YAP laser. The Tm:YAP laser source was near diffraction limited with maximum Q-switched pulse peak power of 190 kW. For second harmonic generation (SHG) of NIR, both periodically poled lithium niobate (PPLN) and lithium tri-borate (LBO) were evaluated, with 58% conversion efficiency and 3.1 W of 970 nm power achieved with PPLN. The PPLN 970nm emission was frequency doubled in 20mm long type I LBO, generating 1.1 W at 485nm with a conversion efficiency of 34%. With LBO used for frequency doubling of 2.3 W of 1888 nm Tm:YAP output to 944nm, 860mW was generated, with 37% conversion efficiency. Using a second LBO crystal to generate the 4th harmonic, 545mW of 472nm power was generated, corresponding to 64% conversion efficiency. To generate the 8th harmonic of Tm:YAP laser emission, the 472nm output of the second LBO was frequency doubled in a 7mm long BBO crystal, generating 110 mW at 236nm, corresponding to 21% conversion efficiency.
We describe and compare the performance of two types of compact, passively Q-switched Yb:YAG 1030nm lasers and their use for 257nm fourth harmonic generation (FHG). In the first implementation, an end-pumped Yb:YAG laser produced a 250μJ pulse train with an average power at 1030nm of 3.6W. Using a 10mm LBO crystal (70% doubling efficiency), followed by a 7mm BBO crystal (45% conversion efficiency), 1.1W at 257nm was generated (overall FHG efficiency of 30%). The second implementation was a side-pumped Q-switched Yb:YAG laser pumped by a 200W diode bar. A 10mm KTP crystal followed by a 6mm BBO crystal resulted a 15% FHG conversion efficiency. The UV emission was in a form of 1-5 Hz PRF, 2ms long burst of 0.2mJ pulses with a 30kHz intra-burst PRF. Within a 1.65ms emission window, an 11.5mJ burst at 257 nm was generated that had a maximum intra-burst power of 7W. This paper will address the merits of each approach for realizing a man-portable laser suitable for ultraviolet Raman explosives detection.
We describe compact and efficient Q-switched diode-pumped, Tm:YAP lasers operating at 1.94μm. Laser CW and Q-switched performance is compared, using both compact mechanical as well as passive Q-switching. For passive Q-switching using a Cr:ZnS saturable absorber (unsaturated transmission of 95%), the laser produced 0.5mJ pulses with an average power of 4.4W and 6.5kW peak power, and had an optical efficiency of 30%. A resonant mirror mechanical Q-switch resulted in a 4 kHz PRF pulse train, with an optical slope efficiency of 52% and an optical-to-optical conversion efficiency of 41%. The laser generated 1.5 mJ, 45 ns FWHM, 33kW peak power pulses, and 6.2W of average output. A second mechanically Q-switched laser operating at 10 kHz PRF produced 1mJ, 35kW peak power pulses, generating 11W average power with an optical efficiency of 46%, and a beam quality of 1.4x diffraction limit.
We describe a compact, side-pumped, Er/Yb glass laser with a low cost mechanical Q-switch. The Q-switch uses a mirror or reflecting prism mounted on a cantilever resonant spring that is driven by a small electromagnetic coil. The demonstrated laser used a 5 mm long Er/Yb glass gain element, and was side-pumped by a 940 nm, 5 mm wide diode bar generating up to 100 W peak power. Target energies of 3mJ have been realized in a near-diffraction limited mode, with pulse widths of 15-25ns, and an optical-to-optical efficiency of greater than 2%. The mechanical Q-switch assembly was fully athermalized via mounting a displacing porro reflector to the cantilever spring, where a 2.5mJ laser was observed to operate with less than 5% variance over -35°C to+60°C.
We present a compact, side pumped passively Q-switched Yb:YAG laser that was operated in a burst mode with pump durations of 2-4 ms at low duty cycles. Intra-pump pulse Q-switched pulse repetition frequencies varied from 5-20 kHz depending on the transmission of the Cr:YAG saturable absorber, which was varied from 70% to 94%. Pump duration, pulse repetition frequency and output coupler reflectivity were optimized to yield maximum Yb:YAG laser average power and laser efficiency, while providing sufficient peak intensity, typically 0.3-1 MW, to enable efficient forth harmonic generation (FHG). Pulse energies and durations were in ranges of 0.3-1.8 mJ and 1.5-7ns, respectively, dependent on the unbleached transmission of the Cr:YAG saturable absorber. We achieved an optical efficiency of greater than 15% for the Yb:YAG laser. Extra-cavity 515 nm second harmonic generation (SHG) was achieved using a 5mm long KTP crystal. The 515 nm light was then frequency doubled by focusing it into a 7mm long BBO crystal, resulting in a 15% conversion efficiency from 1030nm to 257.5 nm, with an average UV power greater than 100 mW.
A compact 1030nm fiber laser for ultraviolet generation at 257.5nm is presented. The laser employs a short length of highly-doped, large core (20μm), coiled polarization-maintaining ytterbium-doped double-clad fiber pumped by a wavelength-stabilized 975nm diode. It is passively Q-switched via a Cr4+:YAG saturable absorber and generates 2.4W at 1030nm in a 110μJ pulse train. Lithium triborate (LBO) and beta-barium borate (BBO) are used to achieve 325mW average power at the fourth harmonic. The laser's small form factor, narrow linewidth and modest power consumption are suitable for use in a man-portable ultraviolet Raman explosives detection system.
A highly compact and low power consuming Q-switch module was developed based on a fast single-axis MEMS mirror, for use in eye-safe battery-powered laser range finders The module’s 1.6mm x 1.6mm mirror has <99% reflectance at 1535nm wavelength and can achieve mechanical angle slew rates of over 500 rad/sec when switching the Er/Yb:Glass lasing cavity from pumping to lasing state. The design targeted higher efficiency, smaller size, and lower cost than the traditional Electro-Optical Q-Switch. Because pulse-on-demand capability is required, resonant mirrors cannot be used to achieve the needed performance. Instead, a fast point-to-point analog single-axis tilt actuator was designed with a custom-coated high reflectance (HR) mirror to withstand the high intra-cavity laser fluence levels. The mirror is bonded on top of the MEMS actuator in final assembly. A compact MEMS controller was further implemented with the capability of autonomous on-demand operation based on user-provided digital trigger. The controller is designed to receive an external 3V power supply and a digital trigger and it consumes ~90mW during the short switching cycle and ~10mW in standby mode. Module prototypes were tested in a laser cavity and demonstrated high quality laser pulses with duration of ~20ns and energy of over 3mJ.
Using a resonant scanner mirror Q-switch to provide a time varying change in cavity alignment, 1535nm lasers based on
Er/Yb-doped glass and 1064nm lasers based on Nd:YAG were evaluated. Using a side pumping architecture, the Er/Yb
glass laser used a compact mechanical Q-switch with a mirror rotation rate of 330 Rad/s, enabling generation of <3 mJ
pulses with a pulse width of 16ns. The laser output was a diffraction limited TEM00 mode. A mechanical Q-switch
based on a MEMS tilting mirror was also used; its performance in a laser cavity was found to be similar to the resonant
mirror. The technique of mechanical Q-switching was also extended to a side pumped Nd:YAG laser (mirror sweep rate
of 1300 Rad/s), enabling generation of Q-switched pulses of <30mJ and 25ns duration. The far-field divergence showed
this laser to be highly multi-moded within the pump plane, with a measured beam-product-parameter greater than 30
We have fabricated prototype frequency tripled Nd:YAG lasers using 808nm Vertical Cavity Surface emitting laser (VCSEL) arrays for end-pumping. The passively Q-switched Nd:YAG laser generated 15mJ pulses with a duration of 2-4 ns. Used as a source for third harmonic generation, the laser produced in excess of 2mJ at 355nm. Of particular concern was the impact of temperature variation on conversion efficiency, which included effects for both the source laser and non-linear crystals. Various solutions to the temperature effects were explored to enable operation of the frequency tripled laser over a wide temperature range.
Laser illumination makes it possible to perform high resolution imaging when ambient light level is insufficient to overcome camera noise. The relatively long coherence length of most lasers, however, causes coherent speckle in the camera image plane, which can result in a significant decrease of the image quality and the maximum achievable target identification range. We characterized several types of NIR and SWIR laser diode illumination sources, with emphasis placed on measuring the properties of coherent speckle observed in the camera image plane. Image plane speckle contrast was measured by illuminating the imaged Lambertian surface with single-mode laser, multi-mode laser, wide-stripe laser with two active junctions and broad-band emission, and NIR and SWIR vertical cavity surface emitting laser (VCSEL) arrays. The impact of various imaging system parameters, including pixel size, imaging lens focal length, F-number, and IFOV on the contrast and characteristic size of the speckle intensity distribution were determined. Speckle contrast dependence on the polarization properties of various reflecting surfaces was measured. The reduction of speckle contrast with increasing source spectral width, and increasing size of spatially incoherent VCSEL emitter arrays will be described. We show that a speckle contrast of 5-10% is achievable for a typical long range SWIR imaging system.
We have explored using 808nm Vertical Cavity Surface emitting laser (VCSEL) arrays for end-pumping of Nd:YAG
lasers. A variety of laser designs were explored including a compact passively Q-switched lasers that produced a 22mJ
pulse having a pulse width of <1.5ns, and an actively Q-switched laser that produced a 40mJ pulse having a 7 ns pulse
width. The VCSEL pumped actively Q-switched laser was used as a source for sum frequency generation. Using a
2mm type II KTP and 3mm type I LBO, we generated greater than 5mJ at 355nm with a 21% THG conversion
During the past few years the Monoblock laser has become the laser-of-choice for Army laser range-finders. It is eyesafe
with emission at 1570 nm, high pulse energy, simple construction, and high efficiency when pumped by a laserdiode
stack, providing advantages that are not available with other laser types. Although the divergence of the
Monoblock output beam is relatively large, it can be reduced to <1 mR using a telescope with a large magnification.
This solution, however, is not acceptable for applications where the laser and telescope size must be kept to a minimum.
In this paper we present a simple and compact technique for achieving significant reduction in the Monoblock beam
divergence using a partial reflector that is placed a short distance from the optical parametric oscillator (OPO). Using
an ultra-compact 38 mm Monoblock with a 10 mm long KTP OPO, we achieved a beam divergence of <4 mR,
corresponding to a >2.5 X reduction from the unmodified laser. Performance using this technique with various feedback
and etalon spacings will be presented. Laser diode array and VCSEL pumping were both investigated with similar
We have explored using UV illumination as a method to mitigate pyroelectric effects, and their associative loss in hold-off
for lithium niobate Q-switch materials under cold temperature operation. It has been observed that by illumination of
the LiNbO3 Q-switch material from the side, the above bandgap light can provide for an increase in conductivity via an
increase in photocarriers. In the presence of strong pyroelectric fields associated with a change in temperature, these
carriers can be effectively swept in the direction to eliminate the field. We quantified the improvement in conduction by
measuring the decay time for the pyroelectric induced loss in extinction. At negative 20°C, the decay rate for the
pyroelectric field in the absence of UV illumination was measured to be 16.7 hours. It was found that by illuminating
the LiNbO3 from the side with two UV LEDs operating at 500mA, the decay constant for a built-up pyroelectric charge
could be reduced to 1minute. With this technique applied to a LiNbO3 Q-switched laser, the laser was shown to perform
over rapid cooling without a degradation in performance.
The method of optical triggering using a brass board architecture for a Q-switched Nd:YAG laser by direct bleaching of
a Cr:YAG saturable absorber was determined to be effective in reducing the pulse-to-pulse timing jitter. A miniaturized
triggering setup was employed to enable the brass board operation of the optically triggered laser. A 3mm wide minilaser
diode bar (1024nm) with collimated emission was mounted on a compact heat sink and used to bleach the Cr:YAG
saturable absorber from a direction orthogonal to the lasing axis. A compact 300A pulse driver, with <0.5 μs rise time
and 3-5 μs duration, was developed for pulsing the 3mm diode bar. These components were combined to demonstrate a
compact brassboard implementation of the optically triggered passively Q-switched laser.
To address the issue of pulse-to-pulse timing jitter in a passively Q-switched Cr:YAG/Nd:YAG laser, we have
developed a technique for optical triggering, where the energy from a single bar diode was used to bleach a thin sheet
within the Cr:YAG saturable absorber from a direction orthogonal to the lasing axis. A strong anisotropy for bleaching
effect was observed; with appropriate polarization of the bleaching light the transmission through the saturable absorber
was increased from 45% to 63%. This technique was applied to a monolithic Cr:YAG/Nd:YAG laser operating under
steady state conditions. By placing the Q-switched pulse at the time corresponding to the steepest slope for change in
transmission during bleaching, which occurs ~1μs after the bleaching diode trigger, we measured an 12.5X reduction in
the pulse-to-pulse timing jitter, from 100ns for free running operation to 8ns with optical triggering.
Recent advances in compact solid sate lasers for laser designation, eye-safe range finding and active imaging are described. Wide temperature operation of a compact Nd:YAG laser was achieved by end pumping and the use of multi-&lgr; diode stacks. Such lasers enabled construction of fully operational 4.7 lb laser designator prototypes generating over 50 mJ at 10-20 Hz PRF. Output pulse energy in excess of 100 mJ was demonstrated in a breadboard version of the end-pumped laser. Eye-safe 1.5 &mgr;m lasers based on flash-pumped, low PRF, Monoblock lasers have enabled compact STORM laser range finders that have recently been put into production. To achieve higher optical and electrical efficiency needed for higher PRF operation, Monoblock lasers were end-pumped by a laser diode stack. Laser diode end-pumped Monoblock lasers were operated at 10-20 Hz PRF over a wide temperature range (-20 to +50oC). Compared with bulk compact solid state lasers, fiber lasers are characterized by lower pulse energy, higher PRF's, shorter pulses and higher electrical efficiency. An example of fiber lasers suitable for LIDAR, and atmospheric measurement applications is described. Eye-safe, low intensity diode pumped solid state green warning laser developed for US Army checkpoint and convoy applications is also described.
The 1620-1700 nm region of the optical spectrum is important as it contains numerous molecular resonance lines of chemical species. We have investigated, theoretically and experimentally, the possibility of designing an efficient tunable wavelength converter (WC) based on a fiber OPA, to generate high-power in that range, by mixing radiation generated by C- and L-band fiber amplifiers.
We have theoretically investigated the possibility of obtaining strong pump depletion in a one-pump fiber OPA, and of maintaining high conversion efficiency as the signal is tuned over a wide range. We have shown analytically that strong pump depletion can be obtained over a broad tuning range, when the signal input power is about one half of the pump input power.
In experiments with a 40-m long highly-nonlinear fiber (HNLF) we have generated 900 mW of CW output power at 1665 nm, when pumping with 3W at 1612nm and 0.82W at 1562nm. The optical conversion efficiency was 23%, and the linewidth was less than 0.1 nm. To our knowledge this is the highest CW output power reported to date for a fiber OPA WC. We have also obtained similar output characteristics at 1684 nm, demonstrating the tunability of the device, which can in principle be tuned over the 1662-1697 nm region by tuning the signal wavelength over the C-band (1535 to 1565 nm). We anticipate that the output power can be scaled to higher powers.
Fiber lasers and amplifiers are used in a variety of applications either for scientific (spectroscopy, medicine...) or industrial applications (free space communications, laser marking and drilling ...). The combination of doped double clad fibers (DCF) and high power multimode semiconductors laser diodes technologies allows to achieve very high output power in very compact, robust and maintenance free systems. Yb 3+ doped DCF are well suited for 1μm wavelength amplification. In pulsed regime, achievable peak power can be strongly limited by nonlinear effects such as Kerr effect, Stimulated Raman Scattering (SRS) or Stimulated Brillouin Scattering (SBS). Consequently, the optimisation of optical amplifier architecture is required. In this paper, we demonstrate performances obtained for the generation of 2ns optical pulses up to >1.7kW peak power in a Master Oscillator Power Fiber Amplifier (MOPFA) configuration. The laser seed signal at 1060nm is emitted out of a single longitudinal mode source with spectral linewidth <0.2nm. The pulse repetition rate can be changed between 3 and 30MHz. The high power stage, based on a 2-stages architecture, allows to deliver >10W average output power with a good beam quality (M2<1.2). No significant limitation due to nonlinear effects of the type of the Kerr effect or SRS appears by means of the optimisation of the final stage’s fiber parameters. Results, such as a concentration of more than 80% of the total output power in a 1nm window around the central wavelength and above all an excellent conservation of the spectral properties of the seed source are demonstrated for a peak power of >1.7kW. These high performances are obtained in a fully-integrated device.
The development of compact mid-IR sources using frequency- converted diode lasers has been demonstrated to be applicable for the ultra sensitive, selective, and real time detection of many trace gas species in the infrared spectroscopic fingerprint region, which contains virtually all the fundamental vibrational modes of molecules. This development of infrared laser sources has taken advantage of recent significant technological advances of semiconductor diode lasers and solid state lasers, new nonlinear optical materials, optical fiber and novel data acquisition techniques. Such sensors are able to detect molecules at the parts-per-billion level in ambient air using infrared absorption spectroscopy either by monitoring trace gases in an open path or multi-pass cell configuration. Real world applications ranging from urban, industrial, rural emission studies to spacecraft habitat monitoring are described.
Pulsed, optically pumped four-constituent Type-II (InAs-Ga1-xInxSb-InAs- AlSb) quantum well lasers emitting at 3.9 - 4.1 micrometer were observed to lase up to 285 K with a characteristic temperature T0 of 35 K for 170 K less than Top less than 270 K. A theoretical analysis predicts dramatic improvements once the potential for suppressing Auger recombination is fully realized.
We describe and present experimental results for two optical control techniques for phased array antennas. The first technique is based on interferometric heterodyning of two narrow- linewidth YAG lasers for the generation of required microwave signal and for simultaneous steering of the radiated beam. The constructed system is simple and well-suited for narrowband applications, and it may be built without any active mechanical components. The measured radiated antenna patterns are in close agreement with the predicted ones. The second technique is a novel and elegant method for implementing a true time-delay function for optical control. It relies on using a wavelength-tunable laser to provide the optical carrier for the microwave signal and a fiber-optic prism--a set of equal delay fibers with differing net dispersion. The relative interelement time-delay (beam angle) adjustment is accomplished by tuning the optical carrier wavelength. The experimental results obtained on a compact antenna range clearly demonstrate beam-steering and true time-delay operation over a two-octave bandwidth.
Rectangular broad area optical traveling-wave amplifiers have been demonstrated to emit 3.3 W CW of diffraction-limited output power when injected with 400 mW of Ti:Sapphire radiation. Improvement in the amplifier characteristics is realized by replacing the rectangular current-pumped contact with a flared or tapered contact, and amplifying a diverging beam. In this fashion, up to 5.25 W CW of diffraction-limited output is obtained from a 200 mW Ti:Sapphire master oscillator.
Broad area traveling wave amplifiers in single-pass and double-pass configurations have been characterized using both analytical and experimental methods. Amplified emission up to 12.0 W in a nearly-diffraction-limited beam was achieved from double-pass amplifiers under short-pulse conditions, and 7.7 W in a nearly-diffraction-limited beam was achieved from single-pass amplifiers under long-pulse conditions.