Tunable Laser Oscillation Research Articles

Self-injection-locked optical parametric oscillator based on microcombs

Narrow-linewidth yet tunable laser oscillators are one of the most important tools for precision metrology, optical atomic clocks, sensing, and quantum computing. Commonly used tunable coherent oscillators are based on stimulated emission or stimulated Brillouin scattering; as a result, the operating wavelength band is limited by the gain media. Based on nonlinear optical gain, optical parametric oscillators (OPOs) enable coherent signal generation within the whole transparency window of the medium used. However, the demonstration of OPO-based Hertz-level linewidth and tunable oscillators has remained elusive. Here, we present a tunable coherent oscillator based on a multimode coherent OPO in a high-Q microresonator, i.e., a microcomb. Single-mode coherent oscillation is realized through self-injection locking (SIL) of one selected comb line. We achieve coarse tuning up to 20 nm and an intrinsic linewidth down to sub-Hertz level, which is three orders of magnitude lower than the pump. Furthermore, we demonstrate that this scheme results in the repetition rate stabilization of the microcomb. These results open exciting possibilities for generating tunable coherent radiation where stimulated emission materials are difficult to obtain, and the stabilization of microcomb sources beyond the limits imposed by the thermorefractive noise in the cavity.

Dual beam transient thermal lens spectroscopy with high repetition pulsed IR-Laser Excitation: Photothermal and fluorescence quantum yields determination

Based on experimental results, we demonstrated that the most widely used model for the description of the dual beam transient thermal lens spectroscopy technique also works well when a high repetition frequency pulsed pump laser is used instead of a commonly employed continuous wave source. For this, for water samples colored with a tartrazine dye, we compared the optical absorbance obtained using a continuous and a pulsed laser source emitting at the same excitation wavelength. A close to 90 % photothermal quantum yield was obtained as a function of the dye concentration. As an application, we measured the near-infrared fluorescence quantum yield spectrum of a CF®800 dye (Biotium) dissolved in water. The thermal lens signal was recorded as a function of the photon’s wavelength using a tunable MAI TAI BB laser oscillator (Spectra Physics) for pumping that generates light pulses of about 80 fs at a repetition frequency of 80 MHz between 710 and 980 nm. The quantum yield spectrum and a comparison of the optical absorbance spectra measured by the thermal lens technique and a conventional transmittance experiment show a significant fluorescence quenching due to water optical absorption.

Emission wavelength selection and tuning in the [formula omitted] manifolds of a Nd:KGd(WO4)2 solid-state laser

We present a Nd:KGW laser with a wavelength selectable intracavity loss scheme comprising a notch filter and external-cavity feedback, which enables distinct continuous-wave laser oscillation regimes. Based on the spectroscopy of the 4F3/2 - 4I11/2 transition in Nd:KGW, we have achieved tunable laser oscillation at either 1067 nm, 1076 nm or 1085 nm corresponding to different spectral peaks of the emission cross-section. An adequate balance of the intracavity loss also allows for dual-wavelength operation at both 1067–1076 nm and 1076–1085 nm peaks, and the inclusion of an additional external reflector permits dual-wavelength oscillation in the vicinity of the main emission peak at 1067 nm. From the external-cavity laser theory perspective, in our approach, the tuning mechanism is treated as an effective intracavity loss instead of an effective reflectivity treatment. The key parameters for further improving the emission wavelength range and tunability are identified and discussed.

Diode-pumped Dy:KPb2Cl5 laser in the middle-infrared spectral region.

A Dy:KPb2Cl5 (KPC) laser oscillating at approximately 4.4 µm under diode laser pumping at 1.7 µm is demonstrated for the first time. A maximum output pulse energy of 1.1 mJ was achieved at 10 mJ of absorbed pump energy. Tunable laser oscillation in the 4.2-4.5 µm spectral range was recorded with this crystal. Limitations of Dy:KPC for laser oscillation due to its challenging thermo-optical properties are discussed. This crystal is a further addition to the range of low-phonon-energy materials doped with Dy ions that can be applied for laser oscillation in the mid-infrared spectral range under direct diode laser pumping.

High-order cylindrical vector beams with tunable topological charge up to 14 directly generated from a microchip laser with high beam quality and high efficiency

Large topological charge optical vortex beams carrying orbital angular momentum have potential applications on optical trapping, optical communication with high capacity, quantum information processing. However, the beam quality is degraded in vortex beams generated with spiral phase plates or resonator mirrors with defect spots and optical conversion efficiency in solid-state lasers is sacrificed by controlling the loss of resonator. It is a big challenge for generating high beam quality, high-order cylindrical vector beams with large topological charge in compact solid-state lasers. Here, high-order cylindrical vector beams [Laguerre-Gaussian (LG) modes with zero degree and order of l, LG0,l] with tunable topological charges up to 14 have been generated in an annular beam pumped Yb:YAG microchip laser by manipulating the pump power-dependent population inversion distribution. Efficient performance with optical efficiency of 17.5% has been achieved. The output power is 1.36 W for a vector-vortex laser with 14 topological charges. The pump power dependent wavelength tunable and dual-wavelength laser oscillation in vector-vortex beams has been observed by controlling the reabsorption loss at 1030 nm. Wavelength tunable, dual-wavelength (1030 and 1050 nm) laser oscillation has been achieved for vector-vortex beams with topological charges of 8, 9, and 10. The laser beam quality factor M2 close to the theoretical value (l + 1) has been achieved for LG0,l vector-vortex beams with tunable topological charges up to 14. This work provides a new effective method for generating large topological charge high-order cylindrical vector beams in solid-state microchip lasers with high efficiency and high beam quality.

A novel laser-induced fluorescence scheme for Ar-I in a plasma.

Here we describe a novel infrared laser-induced fluorescence scheme for the 1s2 state of Ar-I using an 841.052 nm (vacuum) Sacher tunable diode laser oscillator and compare it to an established 667.913 nm (vacuum) 1s4-pumping Ar-I LIF scheme using a master oscillator power amplifier laser [A. M. Keesee et al. Rev. Sci. Instrum. 75, 4091 (2004)]. The novel scheme exhibits a significantly greater signal-to-noise ratio for a given injected laser power than the established scheme. We argue that this is caused by less intense spontaneous Ar-I radiation near the LIF emission wavelength for the 1s2 scheme as compared to the 1s4 scheme. In addition we present an updated iodine cell spectrum around the 1s4 LIF scheme pump wavelength.

Spectral characteristics of a ternary-mixture of dyes in a dye laser pumped by copper vapor laser

The spectral characteristics of a ternary-mixture, composed of Rhodamine 640, Rhodamine 6G and DCM in ethanol and excited by copper vapor laser, are reported. The concentration of each dye in the ternary-mixture was optimized to provide peak emission at 633nm and absorb both wavelengths of copper vapor laser, i.e. 510.6 and 578.2nm. A fluorescence range of 612–679nm with a relatively broad peak at 631–634nm was obtained when concentrations of Rhodamine 640, Rhodamine 6G and DCM in the ternary-mixture were 0.90mM, 0.30mM and 0.90mM respectively. This ternary-mixture of dyes in ethanol, when used as a gain medium in a narrowband, tunable dye laser oscillator, transversely pumped by both wavelengths of a copper vapor laser, provided a spectral tuning range of 620–665nm with an almost flat peak at 630–634nm.

Efficient spectral control and tuning of a high-power narrow-linewidth Yb-doped fiber laser using a transversely chirped volume Bragg grating

A transversely chirped volume Bragg grating (TCVBG) is used for flexible wavelength-tuning of a high-power (>100 W) tunable Yb-fiber laser oscillator. Continuous tuning over 2.5 THz of the narrow-band (13 GHz) signal was achieved by transversely translating the TCVBG during high-power operation without cavity realignment. The laser operated in a single polarization with a beam propagation factor (M(2)) of 1.2. Since the cavity losses remained constant, the high gain fiber laser exhibited excellent power stability (<0.6% relative deviation) over the investigated tuning range. The possibility of considerably increasing the output power and extending the tuning range while maintaining the power stability is discussed.

Tunable S-band erbium-doped triple-ring laser with single-longitudinal-mode operation

We propose and demonstrate a tunable and stable single-longitudinal-mode (SLM) erbium fiber laser with a passive triple-ring cavity structure in S-band operation. The proposed laser is fundamentally structured by using three different lengths of ring cavities, which serve as the mode filters. When a mode-restricting intracavity fiber Fabry-Perot tunable filter (FFP-TF) is combined, the proposed resonator can guarantee a tunable and stable SLM laser oscillation. Moreover, the performances of the output power, wavelength stability, tuning range, and side-mode suppression ratio (SMSR) are studied.

The role of F A1:Ag+ defects in laser light generation and coadsorption of CO and halogen atoms at the KCl and KBr surface sites. First principles calculations

AbstractFA1:Ag+ color center at the low coordination (100) and (110) surface sites of KCl and KBr thin films play an important role in providing tunable laser oscillation and adsorbatesubstrate interactions. Double-well potentials at this site are investigated using ab initio molecular electronic structure calculations. The calculated Stokes shifted (optical transition bands), opticaloptical conversion efficiencies, the probability of orientational destruction, exciton (energy) transfer and Glasner-Tompkins empirical rule suggest that laser light generation is sensitive to (i) the lattice anion, (ii) the coordination number of surface ions, and (iii) the choice of the basis set centered on the anion vacancy. The adsorbate-substrate interactions were found to be dependent on the electronegativity of the adatom and on the lattice anion. Optimised geometries and the coadsorption of CO and (F, Cl, Br, I) on KCl and KBr (100) crystals are presented. Calculated chemisorption energies for CO on the (halogen atom/defect free sites of KCl and KBr (100) crystals) showed that the coadsorption of halogen atom tends to block other adsorbate-substrate interactions at the nearest neighbour sites. Thus if halogen atom coverage increases, the CO prefers to be adsorbed on the K+ site of the KCl and KBr (100) surfaces and on KBr relative to KCl.

Tunable continuous-wave operation of a Cr^3+,Li^+:Mg_2SiO_4 laser

Room-temperature tunable cw laser oscillation of Cr3+ ions in forsterite crystals (Mg2SiO4) codoped with chromium and lithium has been demonstrated, for the first time to the authors' knowledge, in pumping a crystal with a Ti:sapphire laser into the first excited level of Cr3+ ions (4A2-4T2 transition). The laser is smoothly tunable in the region of 1095-1170 nm. A slope efficiency as great as 4.4% has been achieved.

A tunable erbium-doped fiber ring laser with power-equalized output

We propose and demonstrate a tunable erbium-based fiber ring laser with power-equalized output. When a mode-restricting intracavity fiber Fabry-Perot tunable filter (FFP-TF) is combined, the proposed resonator can guarantee a tunable laser oscillation. This proposed laser can obtain the flatter lasing wavelength in an effectively operating range of 1533.3 to 1574.6 nm without any other operating mechanism. Moreover, the performances of the output power, wavelength tuning range, and side-mode suppression ratio (SMSR) were studied.

FA1:La2+ and FA2:Sc2+ color center lasers and color image sensitization at the low coordination (001) surface of AgBr by ab initio calculations

Abstract The twofold potentials of F A1 :La 2+ and F A2 :Sc 2+ color centers at the low coordination (0 0 1) surface of AgBr play important roles in providing tunable laser oscillation and color image sensitization. Double well-potentials at these sites are investigated by using ab initio methods of molecular electronic structure calculations. F A1 :La 2+ and F A2 :Sc 2+ defect containing clusters were embedded in the simulated Coulomb field that closely approximates the Madelung field of the host surface, and the ions that are the nearest neighbors to the F -site are allowed to relax to equilibrium. As far as color center lasers are concerned, the calculated Stokes shifted optical transition bands suggest that the F A2 :Sc 2+ center is more laser active than the F A1 :La 2+ center. An attempt has been made to explain this result on the basis of size of the impurity cation and optical–optical conversion efficiencies. All relaxed excited states of the defect containing surfaces are deep below the lower edge of the conduction band of the ground state defect-free surface implying that both of F A1 :La 2+ and F A2 :Sc 2+ centers are suitable laser defects. The probabilities of orientational destruction of the two centers, which are attributed to the assumed relaxed excited state saddle-point ion configurations along the 〈1 1 0〉 axis, have been found to be approximately identical. Equivalent recording sensitivities are expected from both centers. The F A1 :La 2+ and F A2 :Sc 2+ defect formation energies are calculated, and the Glasner–Tompkins empirical relation was generalized to include the dopant cations. As far as color image formation is concerned, F A1 :La 2+ and F A2 :Sc 2+ color centers increase the sensitizing capabilities of primary dyes and the effect of supersensitizers by lowering the bottom of conduction band of the silver bromide surface. The supersensitizer increases the sensitizing capability of a primary dye in the excited state by increasing the relative yield of quantum efficiency. On the basis of quasi-Fermi levels, the difference in the sensitizing capabilities between the examined dyes in the excited states are determined.

The role of FA:K+ and FA:Na+ defects in laser light generation and color image formation at the (100) and (110) surface sites of AgCl and AgBr.

FA:K+ and FA:Na+ color centers at the low coordination (100) and (110) surface sites of AgCl and AgBr thin films play important roles in providing tunable laser oscillation and color image sensitization. Double-well potentials at these sites are investigated using ab initio molecular electronic structure calculations. Quantum clusters were embedded in simulated Coulomb fields that closely approximate the Madelung fields of the host surfaces, and ions that are the nearest neighbors to the FA defect site were allowed to relax to equilibrium. The calculated Stokes shifted optical transition bands suggest that laser light generation is sensitive to (i) the lattice anion, (ii) the coordination number of surface ions, (iii) the dopant cation, (iv) the vibrational coupling mode, and (v) the choice of the basis set centered on the anion vacancy. An attempt has been made to explain these results in terms of Madelung potentials, electron affinities and optical–optical conversion efficiencies. All relaxed excited states of the defect-containing surfaces were deep below the lower edges of the conduction bands of the ground state defect-free surfaces, suggesting that FA:K+ and FA:Na+ are suitable laser defects. The probability of orientational destruction of the two centers, attributed to the assumed saddle point ion configurations along the 〈110〉 axis, was found to be dependent on the lattice anion, the coordination number of surface ions, and the dopant cation. For optical memories, a high recording sensitivity was assigned to FA:Na+ relative to FA:K+, to the (110) surface relative to the (100) surface, and to AgCl relative to AgBr. The dependence of exciton (energy) transfer on the lattice anion, the coordination number of surface ions, and the dopant cation was clarified. The Glasner–Tompkins empirical rule was generalized to include the surface coordination number and the dopant cation in addition to the lattice anion. As far as color image formation is concerned, the examined supersensitizer was found to increase the sensitizing capabilities of two primary dyes in the excited states by increasing the relative yield of quantum efficiency. The (110) surfaces of AgBr and AgCl were more sensitive than the corresponding (100) surfaces, and the AgBr thin film was found to be more sensitive than that of AgCl. Based on quasi Fermi levels, the difference in the sensitizing capabilities between the examined dyes in the excited states was determined.

The role of FA(I):Tl+ and FA(II):Ga+ defects in laser light generation and photographic sensitization at the low-coordination surface sites of AgBr first principles calculations

Abstract FA(I):Tl+ and FA(II):Ga+ color centers at low coordination surface sites of AgBr thin films play important roles in providing tunable laser oscillation and photographic sensitization. Double-well potentials at these sites are investigated using ab initio molecular electronic structure calculations. Clusters of variable sizes were embedded in simulated Coulomb fields that closely approximate the Madelung fields of the host surfaces, and ions that are the nearest neighbors to the FA defect site were allowed to relax to equilibrium in each case. The calculated Stokes shifted optical transition bands suggest that laser generation is too sensitive to the simultaneous effects of (i) the dopant cations size (ii) the coordination number of the surface ions, and (iii) the choice of the basis set centered on the Br vacancy. An attempt has been made to explain these results in terms of Madelung potentials, electron affinities and optical–optical conversion efficiencies. All relaxed excited states of the defect containing surfaces were deep below the lower edges of the conduction bands of the ground-state defect-free surfaces, indicating that FA(I):Tl+ and FA(II):Ga+ are suitable laser defects. The probability of orientational destruction of the two centers, attributed to the assumed saddle point ion configurations along the 〈1 1 0〉 axis, was found to be directly proportional to the size of the dopant cation, and inversely proportional to the surface coordination number. For optical memories, a high recording sensitivity was assigned to FA(II):Ga+ relative to FA(I):Tl+ and to the flat surface relative to the edge and corner surfaces. The possibility of exciton (energy) transfer between sites of different coordination numbers was clarified. The relaxation and defect formation energies were calculated. The Glasner–Tompkins empirical relation was generalized to include the dopant cations and surface coordination. As far as photographic sensitization is concerned, the highest occupied molecular orbital of only one out of three acyclic developers was found to be high enough for electron transfer to the Fermi level of the silver bromide thin film. The FA defect formation and rotational diffusion of the central silver cluster broaden the energy gaps between the highest occupied molecular orbitals of the developer molecules and the lowest unoccupied molecular orbitals of the defect containing surfaces and make the process of electron injection less facile. About 59% of the reduction of silver ions at the flat surface of silver bromide is attributed to the host anions and FA defect formation, leaving about 41% for the reduction of photoelectrons and developer molecules. The unrelaxed rotational diffusions of the central silver clusters by 30° decrease the latter percentage to about 10%, but are severely hindered by activation energy barriers.

Alexandrite laser pumped LiF:F 2− laser

For the first time to our knowledge a direct alexandrite laser pumping of LiF:F 2 − crystals was suggested and realized by means of energy transfer from the F 3 − to the F 2 − color centers (CCs). Tunable laser oscillation of LiF:F 2 − in the 1000–1300 nm spectral range with a maximum efficiency of 10% was achieved. The process of two-step photo-ionization of the F 3 − CCs under 740 nm excitation was demonstrated experimentally on the basis of the measured decay rate of F 3 − centers. The photo-ionization cross-section from the first excited level of F 3 − centers was calculated to be 2×10 −22 cm 2. Stable output lasing of the LiF:F 2 − laser at room temperature under 793 nm excitation was predicted and realized.

Multiple-return-pass beam divergence and the linewidth equation

A multiple-return-pass equation for beam divergence that is applicable to multiple-prism grating tunable laser oscillators is derived by use of ray-transfer matrices. This beam divergence is then incorporated into the multiple-return-pass dispersive linewidth equation. A discussion of the application of the equation is given.

Tunable grating-coupled laser oscillation and spectral hole burning in an InAs quantum-dot laser diode

Emission spectra are investigated of a low-threshold InAs quantum-dot laser of the dots-in-a-well (DWELL) type operating near 1230 nm. An external dispersion cavity with a diffraction grating is coupled to the laser diode to suppress the subsidiary modes and to tune the central wavelength. A wavelength-dependent competition between the grating-coupled mode and the internal Fabry-Perot modes of the laser suggests that a hole burning in the spectral density of a DWELL laser occurs with a characteristic spectral half width of /spl sim/13 nm (10.5 meV). Simple models of spectral flattening and spectral hole burning are presented to explain the broad free-running and grating-coupled lasing spectra of the DWELL device.

Broad tunability of grating coupled surface-emittinglaser withexternal cavity

The wavelength-tuning properties of an InGaAs grating-coupled surface-emitting laser (GCSEL) are presented. Wide, continuous tunable laser oscillation has been observed over a range of 115 nm, between 900 nm–1015 nm, under pulsed current excitation. Different external cavities have been studied to achieve optimal performance.

Performance characteristics of pulsed single-frequency tunable laser oscillators

The operation of two highly dispersive pulsed tunable dye lasers is reported. Key design features are discussed with reference to laser operational parameters such as linewidth, efficiency and stability. Single-frequency, near transform-limited pulses were obtained with each laser over a range of repetition rates between 10 and 6000 Hz. The performance of the lasers is compared, with regard to possible applications.