Intracavity Laser Research Articles

Actively Q-Switching in the Intra-Cavity Pumping Mechanism for Polarized Oscillation at 2.1 μm

Q-switched and polarized Ho lasers are the ideal driving source for mid-infrared radiation via optical parametric oscillation. Although intra-cavity pumping is an efficient way to achieve the Ho laser oscillation at $2.1~\mu \text{m}$ , which also facilitates the direct use of common diodes in a compact structure, it was demonstrated to be not suitable for Q-switching due to the saturable effect of the Ho-doped gain medium. Here, we report a RbTiOPO4 Q-switched intra-cavity pumped laser via integrating the Tm-doped and Ho-doped gain medium into a composite structure and decoupling the Tm laser from the Ho laser before it was modulated by the RbTiOPO4 crystal. The shortest pulse of 41 ns at repetition frequency of 1 kHz was obtained with a peak power of 7.5 kW. By competing with the intensified self-pulsing, the maximum pulse repetition frequency was found to reach 7 kHz, which was half the driving frequency of the electro-optical modulator. The results pave the way for achieving regular pulses from the intra-cavity pumping mechanism, which facilities a compact, accessible and robust pulse source at $2.1~\mu \text{m}$ .

Linewidth-narrowing of a continuous wave terahertz polariton laser using an intracavity etalon

An uncoated etalon was incorporated within an intracavity continuous wave terahertz polariton laser, leading to a tenfold reduction in linewidth, plus a factor of 2 increase in the THz output power. The increase in output power is explained in terms of phase matching considerations for the parametric downconversion process.

Orthogonally polarized dual-wavelength Nd:YVO4/MgO:PPLN intra-cavity frequency doubling green laser

An orthogonally polarized dual-wavelength laser emitting at 542 nm and 543 nm was proposed and demonstrated. The laser was based on a single Nd:YVO4 crystal and two MgO:PPLN crystals. An optical-to-optical (O-O) efficiency as high as 15.3% was achieved when the powers of the two emission wavelengths were equal. The long-term power stability was 4.5% for 542 nm and 3.5% for 543 nm, respectively. The Laser speckle contrast ratio (SCR) was also measured as a function of power ratio of the two emission wavelengths. The measured SCR values agreed with theoretical simulations with a difference less than 5%.

Temporal soliton and optical frequency comb generation in a Brillouin laser cavity

Temporal cavity soliton generation in fiber cavities or microresonators has achieved great breakthroughs and found significant applications in many fields. Despite recent advances in soliton frequency comb generation via external driving or pump light, it remains challenging to identify a versatile approach for driving the cavity coherently, tuning the mode spacing of soliton frequency combs largely, and achieving long-term operation. Here, instead of using external pump light to drive the cavity coherently, intra-cavity pumping is proposed to drive a Kerr-nonlinear optical cavity for generating temporal solitons and soliton frequency combs. By introducing the Brillouin gain into the cavity, the generated intra-cavity Brillouin lasers are used as the pump light to drive the cavity coherently for generating temporal solitons. In contrast to previous works, the soliton pulses form spontaneously via intra-cavity pumping without the need for fine-tuning the external pump light (to match the cavity resonance), which enables the generation of soliton frequency combs via cascaded four-wave mixing between multiple wavelength intra-cavity Brillouin lasers. Furthermore, by varying the frequency separation of multiple wavelength intra-cavity Brillouin lasers, the soliton pulses with a pulse width of hundreds of femtoseconds and a repetition rate of gigahertz (GHz) to terahertz (THz) are achieved via intra-cavity pumping, corresponding to the generation of soliton frequency combs with step tunable mode spacing from GHz to THz.

Diode-end-pumped solid state ZnWO4 Raman laser at 2254 nm

A diode-end-pumped actively Q-switch intracavity Raman laser with a Tm:YLF laser gain medium and a ZnWO4 Raman gain crystal is demonstrated for the first time. Under the pump power of 30 W at 793 nm, the average output power of 184 mW at first Stokes wavelength of 2254 nm was obtained at a pulse repetition of 2.5 kHz. The corresponding pulse width and output peak power are 5.8 ns and 12.79 kW, respectively. Near-diffraction limited beam quality was observed (M2 ⩽ 1.46).

Cavity-enhanced Raman spectroscopy with optical feedback frequency-locking for gas sensing.

A cavity-enhanced Raman spectroscopy (CERS) gas-sensing method is introduced. Using optical feedback frequency-locking, laser radiation provided by a diode laser is coupled into a three-mirror V-shaped optical cavity. An intracavity laser power of 92 W is realized, yielding a power gain factor of 2200. Raman spectrums of air, carbon dioxide, and acetylene are recorded as a demonstration. Multicomponent gas mixtures including isotopic gases can be simultaneously sensed by CERS. With 200 s exposure time, detection limits of 5.35 Pa for N2, 5.07 Pa for O2, 1.74 Pa for CO2, and 0.58 Pa for C2H2 are achieved. CERS is a powerful gas-sensing method with high selectivity and sensitivity, which also has the potential for quantitative analysis of gases with high accuracy.

Theoretical Study of Quasi-Three-Level Frequency Doubling Laser

Considering the spatial distribution of pumping beam, inverted particle number density, fundamental frequency and photon number density in the cavity of the quasi-three-level frequency-doubled laser, the solution of the rate equation depends on four dimensionless synthetic parameters by normalized correlation parameters. By solving the rate equation numerically, a set of general solutions of the equation are obtained. With these curves and expressions, the design of a quasi-three-level Q-switched intracavity frequency-doubled laser and the prediction of the pulse characteristics could be achieved.

Identification of two new electronic transitions of TaF using intracavity laser spectroscopy

Several bands in two new electronic transitions of TaF have been recorded in high resolution using intracavity laser absorption spectroscopy (ILS). The (1,0), (0,0), and (0,1) bands of the [16.0]0+ – X3Σ−(0+) transition and the (2,1), (1,0), (0,0), (0,1), and (1,2) bands of the [16.3]1 – X3Σ−(0+) transition were observed. TaF was produced in the plasma discharge of a tantalum-lined copper hollow cathode with Ar [1 torr] as a sputter gas and trace of SF6 as a fluoride source. Trace H2 [1%] also was used as it was found to increase the intensity of the observed transitions. The transitions were analyzed using PGOPHER, and the obtained molecular parameters are presented and compared with a previous work.

Dual-wavelength intracavity Raman laser driven by a coaxially pumped dual-crystal fundamental laser.

An actively Q-switched dual-wavelength intracavity Raman laser based on a coaxially pumped dual-crystal (Nd:YAG and b-cut Nd:YAP) fundamental configuration was theoretically and experimentally investigated. Stable dual-wavelength Stokes output at 1176 nm and 1195 nm was subsequently obtained by the Raman conversion from an a-cut YVO4 crystal. A total average power of 1.8 W was produced at 10 kHz pulse repetition frequency under an incident diode pump power of 15.8 W, in which the power levels at the two Stokes wavelengths were nearly equivalent. The power proportion and the interval between the dual-wavelength Stokes pulses could be manipulated actively by changing the pump focal position or pump wavelength.

Mass-independent Dunham analysis of the known electronic states of platinum sulfide, PtS, and analysis of the electronic field-shift effect.

Several new vibrational bands of the [12.5] Ω = 0+-X3Σ- Ω=0+ and the [15.9] B Ω = 0+-X3Σ- Ω=0+ transitions have been observed in high resolution absorption measurements recorded using Intracavity Laser Spectroscopy (ILS). These new bands have been rotationally analyzed and incorporated into a comprehensive PtS dataset that was fit to a mass-independent Dunham expression using PGOPHER. The comprehensive dataset included all reported field-free, gas phase spectroscopic data for PtS, including 32 Fourier transform microwave transitions (estimated accuracy: 1 kHz), 9 microwave/optical double resonance transitions (25 kHz), 51 millimeter and submillimeter transitions (25-50 kHz), 469 molecular beam-laser induced fluorescence transitions (0.003 cm-1), and 4870 ILS transitions (0.005 cm-1). The determined equilibrium constants have been used with the Rydberg-Klein-Rees method to produce potential energy curves for the four known electronic states of PtS. Isotopic shifts in electronic transition energy beyond expectations from the Born-Oppenheimer approximation were observed and treated as electronic field-shift effects due to the difference in the nuclear charge radius between Pt isotopes. The magnitude and sign of the determined field-shift parameters are rationalized through the analysis of the previously reported ab initio calculations.

On the Search for the Electric Dipole Moment of the Electron: P-, T-Odd Faraday Effect on a PbF Molecular Beam

It has been proposed to measure the electric dipole moment of the electron on the basis of the observation of the P-, T-odd Faraday effect on a molecular beam intersecting a cavity using cavity-enhanced intracavity laser absorption spectroscopy. The effective electric field acting on the electric dipole moment of the electron, as well as the molecular parameter of the scalar-pseudoscalar nucleus-electron interaction, has been calculated for the ground and excited electronic states of the lead monofluoride molecule. The simulation of the experiment has shown that the proposed approach allows improving the current bounds on the electric dipole moment of the electron and the scalar-pseudoscalar nucleus-electron interaction constant by six orders of magnitude.

Stable continuous-wave single-frequency intracavity frequency-doubled laser with intensity noise suppressed in audio frequency region**Project supported by the National Key R&D Program of China (Grant No. 2016YFA0301401).

We demonstrated a continuous wave (cw) single-frequency intracavity frequency-doubled Nd:YVO4/LBO laser with 532 nm output of 7.5 W and output of 3.1 W, and low intensity noise in audio frequency region. To suppress the intensity noise of the high power 532 nm laser, a laser frequency locking system and a feedback loop based on a Mach–Zehnder interferometer were designed and used. The influences of the frequency stabilization and the crucial parameters of the MZI, such as the power splitting ratio of the beam splitters and the locking state of the MZI, on the intensity noise of the 532 nm laser were investigated in detail. After the experimental optimizations, the laser intensity noise in the frequency region from 0.4 kHz to 10 kHz was significantly suppressed.

Mass-independent dunham analysis of the [7.7] Y2Σ+ – X2Πi and [16.3] A2Σ− – X2Πi transitions of copper monoxide, CuO

The electronic spectrum of CuO has been studied extensively experimentally. In his review on the spectroscopy of the 3d transition metal oxides (Merer, 1989), Anthony Merer summarized the available experimental data for CuO, which encompassed over 20 publications. There have been 4 subsequent publications on CuO that have included: high resolution Fourier-Transform emission spectroscopy (FTS) (O’Brien et al., 1996), mm- and sub-mm microwave absorption spectroscopy (Steimle et al., 1997), moderate resolution laser induced fluorescence (LIF) spectroscopy (Jin et al., 2002), and high-resolution molecular beam LIF spectroscopy, both in the presence and absence of an external electric field (Zhuang et al., 2010). Despite this extensive study, analyses of spectra have been restricted to 63CuO, even though the natural abundance of 65Cu is significant (63Cu:65Cu is 69%:31%). Additionally, the Λ-doubling parameter for the X 2Πi state of CuO is assigned a negative sign in the FTS analysis, but is assigned a positive sign in the microwave and molecular beam LIF analyses. In this study, high resolution spectra for (0,0) and (1,1) bands of the [16.3] A2Σ− – X2Πi transition of CuO have been recorded using intracavity laser absorption spectroscopy (ILS). Features due to the (0,0) band of 65CuO were clearly identified in the spectra and included in the analysis. The CuO FTS spectrum was retrieved from the archive for the McMath-Pierce Solar Observatory at Kitt Peak, and several additional vibrational bands of the [7.7] Y2Σ+ – X2Πi transition of CuO were identified in the FTS data, including the (1,0), (0,0), and (0,1) bands of 65CuO. The ILS, FTS, microwave and molecular beam LIF data were simultaneously fit to a mass-independent Dunham type Hamiltonian using PGOPHER. In total, 13,019 observations were fit to 1 constrained and 46 floated parameters. The results of this simultaneous fit show a Cu-isotope dependent shift in electronic energy for the [7.7] Y2Σ+ – X2Πi and [16.3] A2Σ− – X2Πi transitions of CuO. The results also confirm that the sign of q in the X 2Πi ground state is negative. Potential energy curves were generated from the molecular constants obtained in the fit for the [7.7] Y2Σ+ and X 2Πi states using the RKR method. These potential energy curves are significantly different and clearly indicate the Y and X state do not form a pure-precession pair.

Tm:YAG Disk Laser Intra-Cavity Pumped by QCW $1 ~\mu$ m Yb:YAG Thin Disk Laser

We report a $2~\mu \text{m}$ Tm:YAG disk-laser intra-cavity pumped by a Yb:YAG thin-disk laser at 1030 nm. The result demonstrates that a thin-disk-shape Tm:YAG crystal can operate with $1~\mu \text{m}$ pumping sources having an extremely low absorption ( $ /mm). The slope efficiency of the $2~\mu \text{m}$ laser with respect to the 940 nm laser diode (pump source of the 1 $\mu \text{m}$ laser) was ~1.05%. We obtained a maximum average power of 760 mW, and a maximum peak power of 2.5 W. As far as we know, this is the first report of a $1~\mu \text{m}$ -laser-pumped disk-shape Tm3+ laser. Our work implied that a low-cost, high-power Tm:YAG thin-disk laser can be implemented by power-scaling through this intra-cavity pumping scheme.

Intracavity-pumped Yb:YAG lasers using the 915-nm absorption line

A nonstandard type of Yb:YAG laser intracavity pumped by an all-solid-state Nd : LuVO4 laser at the wavelength of 916 nm around the 915-nm absorption peak of Yb3 + is presented. A model is derived to improve the 1030-nm output power of the Yb:YAG laser by optimizing the absorption ratio of Yb:YAG at the 916-nm pump wavelength. Both the continuous wave (CW) and pulsed performances of the presented laser are experimentally investigated. At the maximal diode pump level of 18 W, a 5.63-W output power (CW) and a 3.71-W average output power (pulsed) at 1030 nm are achieved, corresponding to optical conversion efficiencies of 31.3% and 20.6%, respectively.

Analysis of the normalization theory of intracavity anti-Stokes laser

Anti-Stokes laser generation is a frequency up conversion. It is a four-wave mixing process of two fundamental photons, one Stokes photon, and one anti-Stokes photon. So, the conversion efficiency of the anti-Stokes laser is low. Therefore, it is particularly important to guide experiments through theoretical optimizations. In this paper, the rate equations under plane wave approximation of intracavity anti-Stokes lasers are normalized. By numerically solving the normalized equations, a group of adaptable curves are obtained to describe the operation of the intracavity anti-Stokes lasers. The influences of the composite variables on the performance of the lasers are analysed.

Rotational analysis of the [15.1] A″–[formula omitted]1A′ transition of CuOH and CuOD observed at high resolution with Intracavity laser spectroscopy

While mentioned briefly in the analysis of the A∼1A′–X∼1A′ transition of CuOH by Jarman et al. (1991), the 6640 Å band system of CuOH has never been rotationally analyzed. In this work, that band system has been observed and recorded in absorption at high resolution using Intracavity Laser Spectroscopy (ILS), and has been assigned as the v″ = v′ = 0 vibrational band of the [15.1] A″–X∼1A′ transition of CuOH. The CuOH molecules were produced in current-regulated RF discharges formed when 0.40 A was applied to a Cu hollow cathode in ∼500 mTorr of O2 with a trace amount of H2. CuOD molecules were produced in a similar fashion with a discharge current of 0.45 A, and a gas mixture that was ∼80:20% O2:D2. The hollow cathode was located within the resonator cavity of a DCM dye laser that was tuned over the 14,500–16,500 cm−1 range with an optically transparent wedge. Pathlengths of ∼10 km were utilized with the ILS method. The (1,0), (0,1), and (1,2) Ka sub-bands with (Ka′,Ka″) of 63CuOH; the (1,0) and (0,1) Ka sub-bands of 65CuOH; and the (2,1), (1,0), (0,1), (1,2) and (2,3) Ka sub-bands of 63CuOD were included in the rotational analysis. The transitions were fit to a Watson S-reduced Hamiltonian using PGOPHER, and the pure rotational transitions for 63CuOH, 65CuOH, and 63CuOD [J. Chem. Phys., 112, 641 (2000)] were included in the fit. The molecular constants determined by the fit were used to calculate an r0 structure for the [15.1] A″ state. A global perturbation was observed for J′ > 20 in Ka = 1 of the [15.1] A″ state of CuOH, but no perturbations were observed for CuOD. Finally, a correlation diagram has been constructed, comparing the observed and calculated electronic states of the isoelectronic species CuF and CuOH.

Experimental study of the dynamics of fast gas heating in a low-pressure DC discharge in nitrogen

This paper discusses the experimental studies of the gas heating dynamics of a low-pressure DC discharge in nitrogen. The time evolution of the discharge current, the electric field, and the gas temperature in the positive column of a pulsed DC discharge in nitrogen for a gas pressure of 1.5 Torr and a current density of 0.1–6 A cm−2 were measured. The gas temperature in the discharge was equal to the rotational temperature in the and metastable electronic states of nitrogen. The rotational temperature in the state was found from the spectra of the first positive system of N2, which were recorded by using intracavity laser absorption spectroscopy. The rotational temperature in the state was determined from the VUV emission spectra of the Lyman–Birge–Hopfield system of N2. The gas temperatures obtained by these two spectroscopic methods were in good agreement. It was found that two phases with different gas heating rates exist during a discharge pulse. In the first phase, the gas heating was relatively slow. With increasing current density, the duration of the first heating phase decreased from 150 μs at 0.2 A cm−2 to 10 μs at 2.5 A cm−2. In the second phase, fast gas heating occurred. The gas heating rate in the second phase increased with increasing discharge current, and was equal to 10 K μs−1 for a current density of about 2 A cm−2. The relation between the rate of the fast heating and the density of deposited power obeyed a power law. In 300 μs, the gas was heated in the discharge up to about 400, 1500, and 3000 K for current densities of 0.2, 1, and 2.5 A cm−2, respectively. These experimental data can be the basis for verification of kinetic models for gas heating dynamics in a low-pressure discharge in nitrogen.

Mass-independent Dunham analysis of the [13.8] Ω = 3/2 − X2Π3/2 transition of platinum monochloride, PtCl, observed by intracavity laser spectroscopy: Periodic trends in the M+X− bonding model (M = Ni, Pt; X = F, Cl)

The first electronic transition of platinum chloride, PtCl, observed at high resolution has been recorded in absorption using Intracavity Laser Spectroscopy (ILS). The PtCl molecules were produced in a current-regulated RF discharge formed when 0.30–0.60 A was applied to a Pt-lined Cu hollow cathode in a ∼1 Torr Ar/He sputter gas mixture, with a trace amount of CCl4 as the chloride source. The hollow cathode was located within the resonator cavity of either a tunable DCM dye laser operated over the 14,500–16,500 cm−1 range or a Ti:Sapphire laser operated over the 12,890–12,990 cm−1 and 13,255–13,365 cm1 ranges. Effective absorption path lengths ranging from 0.6 to 2.0 km were utilized with the ILS method. Eight band systems were identified and rotationally analyzed as the (0,2), (0,1), (3,0), (4,0), (5,0), (6,0), (6,1), and (7,1) vibrational bands of the [13.8] Ω = 3/2 − X2Π3/2 transition of PtCl. The vibrational assignment was confirmed through isotopologue shift analysis. The ILS data and millimeter- and submillimeter-wave data reported by Okabayashi et al. (2012) were fit to a mass-independent Dunham-type Hamiltonian using PGOPHER. Pt-isotope dependent deviations in the Dunham model were observed in Y″01(Be″), Y′01(Be′), and Y′00(Te′) and treated using field-shift parameters, and these parameters are compared to the reported field-shift effects for other 5d transition metal diatomics. The excited state molecular constants determined in this study are consistent with those of the (4) 3/2 state in the computational study by Zou and Suo (2016). The electronic transitions of NiF, NiCl, and PtF analogous to the [13.8] Ω = 3/2 – X2Π3/2 transition of PtCl have been studied both theoretically and experimentally. The vibrational force constants and relative bond lengths for the MX (M = Ni, Pt; X = F, Cl) molecules suggest that Ni and Pt form similar MX bonds, with NiX bonds being slightly stronger, but a large effect is observed for halogen substitution, with MF force constants being more than twice as large as the corresponding MCl values.

Direct excitation of the spin-orbit forbidden X2π3/2 ← X2π1/2 transition in NO using the intra-cavity free electron laser FELICE

We present the direct far-infrared optical excitation of NO radicals from the electronic ground state to the spin-orbit excited state. This spin-orbit forbidden transition at a photon energy near 125 cm−1 borrows intensity by a small admixture of character into the wavefunction, and can be saturated using the intracavity free electron laser FELICE. In the state, the NO radical has a negligible magnetic moment, whereas the radicals have a large magnetic moment in the excited state. The direct optical excitation demonstrated here thus effectively 'switches on' the molecule's magnetic moment, and allows for the production of a sample of NO () with almost perfect quantum state purity. These optically prepared well-defined packets of magnetic NO radicals offer interesting prospects for the use of this benchmark molecule in molecular deceleration and trapping experiments.