Showing papers in "SPIE milestone series in 2002"

Stimulated optical radiation in ruby

Abstract: Schawlow and Townes1 have proposed a technique for the generation of very monochromatic radiation in the infra-red optical region of the spectrum using an alkali vapour as the active medium. Javan2 and Sanders3 have discussed proposals involving electron-excited gaseous systems. In this laboratory an optical pumping technique has been successfully applied to a fluorescent solid resulting in the attainment of negative temperatures and stimulated optical emission at a wave-length of 6943 A. ; the active material used was ruby (chromium in corundum). After demonstration in 1954 of the 'maser' principle (microwave amplification by stimulated emission of radiation), systems were sought in which the effect occurred in the infrared and visible spectrum. This goal was reached in 1960 when Theodore Maiman achieved optical laser action in ruby.

Spectroscopic and laser characteristics of Ti:Al2O3

Abstract: Spectroscopic measurements and laser performance of Ti:Al2O3 are discussed in detail. Data on absorption and fluorescence spectra and fluorescence lifetime as a function of temperature are presented. Laser characteristics observed with pulsed-dye-laser, frequency-doubled Nd:YAG-laser, and argon-ion-laser pumping are covered and show that nearly quantum-limited conversion of pump radiation can be achieved, along with tuning over the wavelength range 660–986 nm.

Optical spectra of transition-metal ions in corundum

Abstract: The polarized optical spectra of the ions Ti3+, V3+, Cr3+, Mn3+, Co3+, and Ni3+ in corundum single crystals have been studied at temperatures from 4.2° to 1200°K. A theory of the band strength based on the point‐charge model and p‐d mixing has been developed and applied to the data with results in fair agreement with experiment. The effects of temperature show that the vibrational‐electronic contribution to band strength is quite small at low temperature but may be appreciable at high temperatures. The crystal‐field parameters have been calculated as convergent lattice sums. The observed trigonal‐field parameter has the opposite sign from that calculated by the point‐charge model if the impurity ion is assumed to occupy an Al3+ ion position in the lattice, but has the same sign as calculated for an ion 0.1 A displaced along the c3 axis toward the empty octahedral site. Details of the spectra have been interpreted as showing that the surroundings of an ion are distorted in some electronic states.

Transition metal-doped zinc chalcogenides: Spectroscopy and laser demonstration of a new class of gain media

Abstract: The absorption and emission properties of transition metal (TM)-doped zinc chalcogenides have been investigated to understand their potential application as room-temperature, mid-infrared tunable laser media. Crystals of ZnS, ZnSe, and ZnTe, individually doped with Cr/sup 2+/, Co/sup 2+/, Ni/sup 2+/, or Fe/sup 2+/ have been evaluated. The absorption and emission properties are presented and discussed in terms of the energy levels from which they arise. The absorption spectra of the crystals studied exhibit strong bands between 1.4 and 2.0 /spl mu/m which overlap with the output of strained-layer InGaAs diodes. The room-temperature emission spectra reveal wide-band emissions from 2-3 /spl mu/m for Cr and from 2.8-4.0 /spl mu/m for Co, Cr luminesces strongly at room temperature; Co exhibits significant losses from nonradiative decay at temperatures above 200 K, and Ni and Fe only luminesce at low temperatures, Cr/sup 2+/ is estimated to have the highest quantum yield at room temperature among the media investigated with values of /spl sim/75-100%. Laser demonstrations of Cr:ZnS and Cr:ZnSe have been performed in a laser-pumped laser cavity with a Co:MgF/sub 2/ pump laser. The output of both lasers were determined to peak at wavelengths near 2.35 /spl mu/m, and both lasers demonstrated a maximum slope efficiency of approximately 20%. Based on these initial results, the Cr/sup 2+/ ion is predicted to be a highly favorable laser ion for the mid-IR when doped into the zinc chalcogenides; Co/sup 2+/ may also serve usefully, but laser demonstrations yet remain to be performed.

Ytterbium solid-state lasers: The first decade

Abstract: The spectroscopic and laser kinetic properties of the trivalent ytterbium ion in various solid-state media are reviewed. Contrasts between four- and quasi-three-level lasers (e.g., Nd:YAG versus Yb:YAG) are highlighted. Various architectures suitable for use in high-brightness high-power Yb:YAG lasers are examined, and achieved laser performance levels are summarized. The properties of alternative ytterbium-doped laser gain media are reviewed, and early laser results are cited.

On the absorption spectra of complex ions. II

Abstract: The secular determinants obtained in the previous paper are solved for the energy levels which are important in the absorption spectra of the normal complex ions, leaving the crystalline field strength as a parameter. The values of B and C (Racah's parameters) there needed are determined from the observed spectra of free ions or in some cases by extrapolation. The f -values of the transitions which connect the energy levels calculated are estimated and compared with the observed intensities. The difference of the spectral width among absorption bands and lines is also considered using the energy diagram obtained. Following the assignments determined by the above considerations, the calculated positions of lines and bands are rather in good agreement with the experimental data in divalent ions [MX 6 ] 2+ (M=Cr, Mn, Fe, Co, Ni), when we adjust the crystalline field parameter D q suitably. In trivalent ions [MX 6 ] 3+ (M=Ti, V, Cr, Mn, Fe), it is necessary besides the adjustment of D q to use smaller values ...

Efficient, broadly tunable, laser-pumped Tm:YAG and Tm:YSGG cw lasers

Abstract: Broadly tunable cw laser emission is reported in Tm:YAG and Tm:YSGG at room temperature with Ti:sapphire laser pumping. The Tm3+3F4 → 3H6 transition is tuned continuously over the ranges 1.87–2.16 μm in YAG and 1.85–2.14 μm in YSGG. Smooth tuning results from overlapping transitions between phonon-broadened crystal field Stark levels.

Laser action in chromium-activated forsterite for near-infrared excitation: Is Cr4+ the lasing ion?

Abstract: Room‐temperature pulsed laser action has been obtained in chromium‐activated forsterite (Cr:Mg2SiO4) for excitation of the near‐infrared absorption band of the system by the 1064 nm radiation from a Nd:YAG laser. The characteristics of laser emission are similar to those observed for 532 nm pumping. It is suggested that the laser action is due to a ‘‘center’’ other than the trivalent chromium (Cr3+), presumably the tetravalent chromium (Cr4+).

Chromium-doped forsterite laser pumped with 1.06 μm radiation

Abstract: Laser action in chromium‐doped forsterite (Cr: Mg2SiO4), pumped with a 1.064 μm Nd:YAG laser, was demonstrated for the first time. The free‐running laser emission is centered at 1.221 μm and has a spectral width of 28 nm. An efficiency of 8% has been achieved with an uncoated crystal produced by the laser‐heated‐pedestal growth method. The available evidence suggests that the laser action is due to Cr4+ in tetrahedral sites.

Ultraviolet solid-state Ce:YLF laser at 325 nm

Abstract: We describe the first reported observation of stimulated emission from a 5d-4f transition in a triply ionized rare-earth-doped crystal. Ce(+3) ions in LiYF(4) (YLF), optically pumped at 249 nm, emitted at 325.5 nm, the shortest wavelength yet obtained from an optically pumped solid-state laser. The large fluorescence linewidth of the laser transition makes the Ce:YLF laser a potentially tunable source of coherent near-ultraviolet radiation between 305 and 335 nm.

Ce3+-doped colquiriite: A new concept of all-solid-state tunable ultraviolet laser

Abstract: In this letter the first performance of tunable solid-state ultraviolet laser, based on 5d-4f transitions of Ce3+ ions in a colquiriite LiCaAlF6 single crystal, is reported. Our findings hold promise for devising a tunable u.v. all-solid-state laser pumped by the fourth harmonic radiation of any commercially available Nd laser.

Continuous-wave laser operation and quantum efficiency of titanium-doped sapphire

Abstract: Cw laser action of Ti:Al2O3 under argon-ion laser pumping is presented. We analyze the free-running characteristics and the effective emission cross section of the laser. The temperature dependence of the 2E lifetime was measured from 4 to 650 K and is explained in a single-phonon model. The quantum efficiency of Ti:Al2O3 at room temperature is 80%.

Lasing due to impurity color centers in yttrium aluminum garnet crystals at wavelengths in the range 1.35-1.45 μm

Abstract: Low-threshold wide-band lasing was achieved for a YAG crystal with optically and thermally stable color centers. The absorption and luminescence spectra were determined, and the gain was measured in the range of wavelengths corresponding to the color-center luminescence. The cross section of the lasing transition was estimated (8 × 10−19 cm2) and the efficiency of conversion of the pump radiation from a neodymium laser into the output radiation was determined (10%).

Flashlamp pumped Cr:LiSrAlF6 laser

Abstract: Tunable, flashlamp‐pumped laser properties are discribed for the crystal Cr:LiSrAlF6 (Cr:LiSAF) in both long pulse and Q‐switched modes of operation. Slope efficiencies of 5%, overall efficiency of 3%, and a tuning range from 780 to 1010 nm are reported.

Characteristics and kinetics of laser-pumped Ti:Sapphire oscillators

Abstract: The experimental performance of a gain-switched Ti:sapphire laser oscillator pumped by a frequency-doubled Q-switched Nd:YAG laser system is presented for a variety of operating conditions. A theoretical model developed for this oscillator predicts well its performance. The observed curved input-output energy plots for the oscillator result from the kinetics of gain switching and fluorescence decay during the gain buildup period. Fluorescence decay also produces observed oscillator thresholds higher than those normally predicted by the standard gain-equals-loss condition. Gain-switched parasitic modes, with a higher threshold but shorter round-trip time than the resonator mode, cause the resonator mode to oscillate only over a finite range of pump energies. Spectroscopic investigations show that the Ti:sapphire cross-section spectrum is well fit by a Poisson distribution, giving a peak cross section of 3*10/sup -19/ cm/sup 2/ for the pi polarization. >

Diode-pumped tunable Yb:YAG miniature lasers at room temperature: Modeling and experiment

Abstract: We present a simple design rule for diode-laser pumped quasi-three-level lasers by using the M/sup 2/ factor. The validity of this model was demonstrated by diode-pumped Yb:YAG laser experiments. The maximum output power of 1.33 W and optical slope efficiency of 63% were obtained in a 400-/spl mu/m Yb:YAG chip miniature laser. Using a 200-/spl mu/m Yb:YAG chip, a 70% optical slope efficiency was reached. In a coupled-cavity configuration, with a quartz birefringent tuning filter, 8.2 THz (29 nm) of tuning was obtained at room temperature. By changing to a calcite birefringent filter, single-axial-mode oscillation with an output power of 500 mW was observed.

Phonon-terminated optical masers

Abstract: The characteristics of phonon-terminated coherent oscillation associated with ${\mathrm{Ni}}^{2+}$, ${\mathrm{Co}}^{2+}$, and ${\mathrm{V}}^{2+}$ ions in rutile and perovskite fluorides are described. Continuous tunability over portions of the vibronic continuum of ${\mathrm{Ni}}^{2+}$ in Mg${\mathrm{F}}_{2}$ has been demonstrated. The system has been thermally tuned in discontinuous segments over a total wavelength span from 1.62 to 1.80 \ensuremath{\mu}, the longest continuous segment being 250 \AA{} (82 ${\mathrm{cm}}^{\ensuremath{-}1}$). Alternatively, a frequency-selective element (prism) has been used to vary the oscillation frequency (at a fixed temperature of 85\ifmmode^\circ\else\textdegree\fi{}K) in discontinuous segments between 1.62 and 1.84 \ensuremath{\mu}. The discontinuities are a consequence of structure present in the vibronic continuum of ${\mathrm{Ni}}^{2+}$ in Mg${\mathrm{F}}_{2}$. Continuous-wave oscillation has been obtained from ${\mathrm{Ni}}^{2+}$ ions in Mg${\mathrm{F}}_{2}$ and Mn${\mathrm{F}}_{2}$, requiring, respectively, less than 65 and 240 W of power into a tungsten lamp. Both systems display continuous spiking, and the spectral distributions of maser emission may be very complex.

Phonon-terminated coherent emission from V2+ ions in MgF2

Abstract: Infrared fluorescence and phonon‐terminated stimulated emission from V2+ ions in MgF2 is reported. Fluorescence is produced in transitions from the first excited state 4T2(4F) to the ground state 4A2(4F). Stimulated emission occurs in the vibronic sideband at 1.1217 μ (8915 cm−1) and lies 1166 cm−1 from the no‐phonon line. A gain curve calculated from the optical spectra predicts an oscillation frequency in reasonable agreement with the observed frequency, with a cross section for stimulated emission of 8×10−21 cm2. From the effect of excited state absorption on the gain profile it is concluded that the excited state absorption cross section at the maser frequency is <3×10−21 cm2.

Simultaneous multiwavelength operation of Nd:YAG laser

Abstract: Operation of pulsed Nd:YAG laser simultaneously at 1.052, 1.061, 1.064, and 1.074 μm is reported. The suppression of the weaker lines by the strongest line (1.064 μm) is avoided by using a cavity scheme which disperses the frequency components transversely in the crystal. The frequency doubling of this radiation in KDP provides several new lines.

All-solid-state tunable ultraviolet subnanosecond laser with direct pumping by the fifth harmonic of a Nd:YAG laser

Abstract: We report what we believe is the first all-solid-state tunable ultraviolet laser pumped by the fifth harmonic of a Q-switched Nd:YAG laser. Our laser based on a Ce3+:LiLuF4 active medium stably generates a single, satellite-free, 0.88-ns pulse under 5-ns, 10-Hz repetition rate pumping conditions. A novel tilted-incident-angle side-pumping scheme resulted in a simple laser-cavity design.

Ultraviolet laser emission properties of Ce3+-doped LiSrAlF6 and LiCaAlF6

Abstract: The UV laser properties of trivalent cerium-doped LiSrAlF6 (Ce:LiSAF) and LiCaAlF6 (Ce:LiCAF) are reported. The polarized absorption, emission, and excited-state absorption cross sections for both Ce:LiSAF and Ce:LiCAF were determined for the 266-nm pump and 290-nm laser emission wavelengths. The single-exponential emission lifetime was measured to be 28 ± 2 and 25 ± 2 ns for Ce:LiSAF and Ce:LiCAF, respectively. The gain was found to be highest when the probe was polarized parallel to the optical axis of the crystal, owing to the anisotropic nature of the excited-state absorption. The excited-state absorption was ascribed to a transition from the 5d orbital of Ce3+ to the conduction band of the host. Laser slope efficiencies as high as 29% and 21%, respectively, were measured for Ce:LiSAF and Ce:LiCAF when the 266-nm pulsed pump beam was polarized parallel to the optical or the c axis. These are the highest laser slope efficiencies yet observed to our knowledge for any known solid-state UV laser material. When the pump beam was polarized perpendicular to the optical axis of the crystals, the gain and the laser efficiencies dropped by as much as an order of magnitude. The magnitude of pump-induced solarization was found to be highly variable for different crystals and to have an insignificant effect on the laser performance when favorable crystals were used.

Diode-pumped spatially dispersed broadband Cr:LiSGAF and Cr:LiSAF c.w. laser sources applied to short-coherence photorefractive holography

Abstract: We demonstrate a novel high power broadband laser source for low coherence interferometry that is based on a simple three mirror diode-pumped c.w. Cr 3+ laser. The cavity design utilises a single intracavity prism to spatially disperse the oscillating laser mode within the pumped region of the laser crystal in order to counteract spectral gain narrowing. We demonstrate continuous wave spatially coherent output beams with spectral widths as wide as 37 nm, which are tunable across the gain linewidth of the laser. Using a single 100 μm stripe width 670 nm diode pump laser we obtained output powers up to 105 mW for incident pump powers of 410 mW. We demonstrate the application of this source (adjusted for a 13 nm bandwidth output) to 3-D imaging through a diffuse medium using photorefractive holography.