Infrared multiphoton dissociation of difluorosilane

Infrared (IR) multiphoton absorption and dissociation of difluorosilane molecules under the action of a pulsed transversely excited atmospheric CO₂ laser were experimentally studied. It has been found that the multiphoton absorption is strongly saturated due to the rotational bottleneck effect. Isotope-selective IR multiphoton dissociation of difluorosilane was performed at 977.2 cm^-1. The dissociation rate for ²⁸SiH₂F₂ isotopomer has been found to be about twice as high as for the other isotopomers at this wavelength. PACS 82.50.Bc; 82.30.Lp     

Recording of a hologram by using the second-order nonlinearity

The observation of “spatial-modulation” resonances of saturated absorption in the interaction of iodine-127 vapors with a superposition of frequency-nondegenerate TEM₀₁ and TEM₁₀ transverse modes of a linear laser is reported. The modulation of the total radiation power of the probing wave, recorded at twice the beating frequency of transverse modes of the laser, is interpreted to be the result of the transformation of modulation of the spatial distribution of the field into its amplitude modulation under the action of nonlinearly absorbing iodine vapors. Resonances of saturated absorption of the weak line R(127)11-5 of iodine-127 (633 nm) in an extracavity cell are observed by the method proposed.     

Frequency stabilization of an internal mirror HeNe laser at 543.5 nm to I2-Saturated absorptions

An internal mirror green HeNe (GRENE) laser at 543.5 nm has been frequency stabilized to I₂-Doppler free absorption signals with a frequency stability of few parts in 10¹⁰. The saturated absorption signals were detected using doubly-differential saturated absorption which eliminates the Doppler background and allows first-derivative locking methods. Two absorption lines R(12)26-0 and R(106)28-0 of ¹²⁷I² were investigated and the hyperfine structure was resolved. Random polarization flips of the GRENE were suppressed by applying a transverse magnetic field to the laser tube near the anode.Present address: Physikalisch-Technische Bundesanstalt, Bundesallee 100, D-3300 Braunschweig, Fed. Rep. Germany     

IR absorption measurements and new FIR emission lines in CH3OH by use of a frequency-tunable CW waveguide CO2 laser

The IR absorption in CH₃OH in the vicinity of CO₂ laser lines has been measured quantitatively by use of a 300 MHz tunable waveguide CO₂ laser with output powers of about 3 W. Information on frequency offsets from the CO₂ line centers, small signal and saturated absorption coefficients of FIR laser pump transitions is obtained. Some stronger pump transitions with frequency offsets larger than 50 MHz gave rise to the observation of 8 new FIR emission lines with wavelengths from 43 to 125 μm.     

Intracavity-frequency-doubled Q-switched and mode-locked Nd:Lu0.15Y0.85VO4/KTP green laser with AO modulator and central SESAM

By using mixed crystal Nd:Lu_0.15Y_0.85VO₄ as laser medium, KTP as frequency-doubling crystal, a diode-pumped intracavity-frequency-doubled Q-switched and mode-locked (QML) Nd:Lu_0.15Y_0.85VO₄/KTP green laser with acousto-optic (AO) modulator and central semiconductor saturable absorption mirror (C-SESAM) is realized by using a V-type cavity. The QML laser characteristics such as the pulse width, single-pulse energy, have been measured for different modulation frequencies of the AO modulator. In comparison with the singly passively QML green laser with central SESAM, the doubly QML green laser can generate more stable and shorter pulses with higher peak power. Based on the coupled rate equations for a diode-pumped doubly QML green laser with AO and C-SESAM, in which the saturated absorption mechanism of C-SESAM is considered, the recurrence relation of the relative amplitude of the mode-locking pulses is given and the related numerical simulations are in good agreement with the experimental results.     

Effect of laser dye deterioration on performance

A previous analysis that described loss of gain in a dye solution as a result of photochemical decomposition by pump photons is refined and is extended to the situation where impurities absorb at the pump wavelength. A limitation in the first paper is that it described only a single absorption depth in the medium at a constant pump fluxI _p. The present examination includes the fall-off ofI _p and integrates the total signal output with depth for a single-pass amplifier operated in the fully saturated gain condition. The equations are simpler, but as before loss of output, expressed in terms of a quantum yield of laser decayQ _L, is minimized for a photochemically bleachable dye, and for one with high gain. Pumping in the vicinity of the absorption maximum is also advantageous.     

External satellites of superfine-structure multiplets in the saturated absorption spectrum of the SiF4 molecule

Earlier-discovered weak satellites of the superfine structure of the saturated absorption spectrum of SiF₄ in the range of oscillation frequencies of a low-pressure CO₂ laser operating at P(38) line of 9.7-μm band are investigated experimentally. The amplitude of the satellites is found to increase relative to that of resonances of the multiplet itself with an increase in the laser power. Within the experimental error, the relative amplitude of the satellites is independent of SiF₄ gas pressure. Possible interpretations of the satellites are discussed.     

Absolute frequency measurement of a CO2/OsO4 stabilized laser at 28.8 THz

A cw carbon dioxide laser operating on the 10 μm R(0)_I transition (28.832 THz) was frequency stabilized by a servo lock to the saturated absorption dip of the Q(15) transition of ¹⁸⁸OsO₄. The laser frequency was measured with a cesium-clock-based frequency chain. In addition, the absorption line frequencies Q(14) of ¹⁸⁸OsO₄ and sQ(4,3) of ¹⁵NH₃, were measured relative to the frequency of Q(15). Received: 21 August 2000 / Revised version: 15 January 2001 / Published online: 30 March 2001     

CW ultraviolet saturation spectroscopy of the 6p 3P0-9s 3S1 transition in mercury at 246.5 nm

We have measured the even isotope structure of the 6p ³P₀-9s ³S₁ transition in mercury at 246.5 nm using saturated absorption spectroscopy with radiation produced as the sum frequency of a 363.8 nm argon ion laser and an LD700 ring dye laser in ADP. This is the first use of cw sum-frequency mixing in nonlinear laser spectroscopy in the ultraviolet. No previous cw Doppler-free measurements have been reported at wavelenghts below 294.5 nm     

A simple extended cavity diode laser for spectroscopy around 640 nm

We report on an extended cavity diode laser for operation near 640 nm. The laser is continuously tunable in 10 GHz ranges with a maximum output power of 3 mW. The laser system has been constructed using off-the-shelf optoelectronic components and easily machinable mechanical parts. The constructed system has been used to study the saturated absorption of the closed 1s₅–2p₉ neon transition in a radio-frequency discharge that can be maintained at neon pressures down to 10⁻² Pa.     

Selective detection of minor isotope lines in saturated absorption spectra by absorption filtering of major isotope lines

We demonstrate a simple method that can be used to detect minor isotope lines in a saturated absorption spectrum by the absorption filtering of major isotope lines. We investigate this method for use in the spectroscopy of the ¹S₀-¹P₁ transition in Yb at 399 nm by controlling the density of Yb atoms by varying the discharge current of a hollow cathode lamp. The performance of an extended-cavity laser diode using a high-power ultraviolet diode chip is also analyzed.     

Topological insulator as an optical modulator for pulsed solid‐state lasers

Topological insulators are states of quantum matter that have narrow topological nontrivial energy gaps and a large third‐order nonlinear optical response. The optical absorption of topological insulators can become saturated under strong excitation. In this work, with Bi₂Se₃ as an example, it was demonstrated that a topological insulator can modulate the operation of a bulk solid‐state laser by taking advantage of its saturable absorption. The result suggests that topological insulators are potentially attractive as broadband pulsed modulators for the generation of short and ultrashort pulses in bulk solid‐state lasers, in addition to other promising applications in physics and computing.     

Saturation spectroscopy of hydrogen 1-011-011-01lines with a multi-mode cw dye laser

With an intense, broadband multi-mode cw dye laser collisional studies of H_α fine-structure resonances with saturated absorption are extended to He buffer gas pressures larger than 30 mbar (0°C). The broadening and shift of the two prominent H_α(2P?3D) transitions are measured in a (He+4% H) gas discharge. The absolute magnitude and the differences in the width of the lines are explained theoretically by different inelastic fine-structure transfer cross sections which can also be deduced from the pressure effect data. Nuclear polarization of hydrogen atoms by H_α optical pumping and polarization transfer to the H(1S) ground state via Ly-α decay and further applications of the multimode laser are discussed.     

Absolute frequency measurement of CO2 laser lines with a femtosecond laser comb and new determination of the CO2 molecular constants and frequency grid

Absolute frequency measurements of a CO₂ laser stabilized on saturated absorption resonances of CO₂ laser lines are reported. They were performed using a femtosecond-laser frequency comb generator and two laser diodes at 852 and 782 nm as intermediate oscillators, with their frequency difference phase-locked to the CO₂ laser. Twenty ¹²C¹⁶O₂ laser lines in the P and R bands at 9 μm were measured with a relative uncertainty of a few 10⁻¹² limited by the CO₂ frequency reproducibility. A new determination of the CO₂ molecular constants was obtained from these data and previous measurements in the 10 μm band. The CO₂ frequency grid was also calculated, with an improvement of two orders of magnitude compared to the previous grid of Maki et al. [J. Mol. Spectrosc. 167 (1994) 211].     

Measurement of the electric dipole moment of NO (X2 Π ν = 0,1) by mid-infrared laser magnetic resonance spectroscopy

A pair of parallel Stark plates are added to a CO laser magnetic resonance spectrometer to apply electric field in the absorption cell. This apparatus is used to measure the molecular electric dipole moment via Zeeman and Stark effects simultaneously. The saturated absorption spectra of NO (X²Π_3/2, ν = 1 ← 0) was observed and the electric dipole moments of NO were directly measured in the presence of an electric field. The dipole moments are determined as μ₀(ν = 0) = 0.1595(15) D, μ₁ (ν = 1) = 0.1425(16) D. The electric dipole moment of the vibrationally excited state (ν = 1) is determined for the first time. The dependence of the electric dipole moments on its nuclear distances is interpreted.     

A phase-sensitive technique to measure small changes in laser frequency: application to measure the shift and broadening of a saturated absorption line of OsO4

A phase-sensitive technique was used to measure the sensitivity to operating conditions of the output frequency of a highly stable carbon dioxide laser, which operated on the 10-μmm R(0) transition (28.8 THz) and was locked to the saturated absorption of the Q(15) transition of OsO₄. Periodic changes in the operating conditions were imposed on the laser and the resulting changes in the output frequency were measured through phase-sensitive demodulation of the heterodyne beat with a second CO₂ laser of much lower stability. Shifts as small as 50Hz could be detected by this technique. The results are in good agreement with previous measurements which employed an infrared frequency chain.     

Effect of laser dye deterioration on performance

Loss of gain in a dye medium as a result of decomposition by pump photons is considered in terms of disappearance of dye molecules and the appearance of a new, single chemical product having absorption in the fluorescence band. The cases of small signal gain and saturated gain are applied to a single pass through a transversely excited amplifier. Loss of output, defined as “quantum yield of laser deterioration”,Q _L , is related to the true quantum yield of molecular destruction of the dye,Q _M , and other known parameters. For the experimentally common, saturated gain condition, the smallestQ _L can be isQ _M , which requires a photochemically bleachable dye with high gain, preferably at high concentration, in a long cavity, operating at high injection and pumping fluxes. Reversing these conditions, the highest valueQ _L can be, compared withQ _M , is unrestricted. This work was performed under the auspices of the U.S. Energy Research and Development Administration. Contract No. W 7405 Eng 48.     

Collisional broadening and shifting of saturated absorption resonances in silicon tetrafluoride

The broadening and shifting of 12 saturated absorption resonances of the SiF₄ gas induced by molecular collisions have been measured in the lasing region of a low-frequency CO₂ laser at the P(30) line of the 9.4-μm band. Values of the collisional broadening are identical accurate to the measurement uncertainty. The collisional shift does not exceed 10% of the collisional broadening. This means that collisions with changes in the internal energy of molecules prevail over dephasing collisions.     

Pulsed optoacoustic detection of multiple photon excitation in molecules

Multiple photon excitation, saturation, and linear absorption of SF₆-argon mixtures when irradiated by a high power CO₂ TEA laser is investigated using a pulsed optoacoustic technique. At low intensities the expected linear dependence of the absorption on laser intensity is observed. At intermediate intensities the absorption exhibits a square root dependence on the incident laser intensity, a dependence which is typical for saturation of an inhomogeneously broadened absorption. At even higher intensities, the absorption shows an intensity dependence typical of multiple photon excitation. The laser intensity was varied between 0.016 kW/cm² and 5 MW/cm², values lower than that needed to produce multiple photon dissociation of SF₆. Increasing the collision frequency of the absorbing molecules with an inert buffer gas is observed to quench the multiple photon excitation.     

High power diode-side-pumped rod Nd:GdVO4 laser

A compact high power diode-side-pumped Nd:GdVO₄ laser has been presented, which can generate an output power of 52 W at 1.063-μm for continuous-wave (CW) operation. The absorption characteristics of the Nd:GdVO₄ in different pump directions is measured, which were used to optimize the diode-side-pumped Nd:GdVO₄ laser head. The laser characteristics of both CW and Q-switched Nd:GdVO₄ and Nd:YAG in are compared and it was found that Nd:GdVO₄ may surpass Nd:YAG for high power laser application.