Raman Laser System Research Articles

Optical single-sideband (OSSB) Raman laser system based on an atomic filter for atom gravimeters.

Phase-modulator-generated laser for Raman transition is widely used in atom gravimeters to simplify a system and improve robustness. However, the induced additional sidebands (ASBs) lead to systematic errors in gravity measurement. This work presents a novel, to our knowledge, method to generate an optical single-sideband (OSSB) laser for Raman transition through phase modulation based on a Faraday anomalous dispersion atomic filter (FADOF). The experimental result indicates that it can reduce the additional sidebands with a signal-to-noise ratio (SNR, the intensity ratio of carrier and unwanted sidebands) of better than 50 dB, and the phase shift caused by ASBs is demonstrated to be effectively suppressed from 358.8 to 2.2 mrad. Furthermore, this system has already been applied on an atom gravimeter to achieve a primary gravity measurement. It shows that the FADOF-based Raman laser system is a new scheme for a compact atom absolute gravimeter.

The Frequency-stabilized Raman Laser System Based on Isotope Atom Saturated Absorption Spectrum

The Frequency-stabilized Raman Laser System Based on Isotope Atom Saturated Absorption Spectrum

139 GHz UV phase-locked Raman laser system for thermometry and sideband cooling of 9Be+ ions in a Penning trap

We demonstrate the phase locking of two ultraviolet (UV) laser sources by modulating a fundamental infrared (IR) laser with fourth-order sidebands using an electro-optic modulator and the phase locking of one sideband to a second fundamental IR laser. Subsequent sum frequency generation and second harmonic generation successfully translates the frequency offset to the UV domain. The phase lock at 139 GHz is confirmed through stimulated Raman transitions for the thermometry of 9Be+ ions confined in a cryogenic Penning trap. This technique might be used for the sideband cooling of single 9Be+ ions as well as sympathetic cooling schemes and quantum-logic-based measurements in Penning traps in the future.

Phase locking technology for Raman laser system based on 1560 nm external cavity lasers

The technology of generating Raman laser is not only an important research content in the field of quantum precision measurement, but also a core technology of quantum inertial sensors such as cold atom gravimeter, gyroscope. For <sup>87</sup>Rb atoms, two 780-nm lasers with a frequency difference of 6.834 GHz and a stable phase are needed to generate Raman light. Raman lasers can be generated by optical phase-locked loops of two 780-nm narrow linewidth external cavity tunable semiconductor lasers (ECDL). But the system thus developed is complicated in structure and very poor in environmental adaptability. The other method to generate Raman laser is based on intracavity 1560-nm laser with frequency doubling and electro-optic modulation technology. This system is simple in structure and strong in environmental adaptability, but it will introduce sideband effects and cannot achieve phase lock due to the limit by the linewidth and feedback bandwidth performance of the laser. In view of this, based on two new 1560-nm external cavity lasers and a home-made phase-locked circuit, in this paper the phase lock of the laser is achieved, and a Raman laser with low phase noise is obtained. The phase noise of beat note signal is as low as –95 dBc/Hz at the Fourier frequency in a range from 1 kHz to 10 kHz. A comparison of this system with the phase-locked performance of the 780-nm dual laser and the hybrid dual laser shows that this scheme has a slight advantage. In addition, the effect of the phase-locking performance on the phase noise of the cold atom interferometer through the method of piecewise integration is analyzed in this work. The experimental results given in this work provide a scheme for developing a miniaturized Raman optical system suitable for external fields.

Design and Experiment of Raman Laser System for Atom Interferometric Measurement

Design and Experiment of Raman Laser System for Atom Interferometric Measurement

YVO4 cascaded Raman laser for five-visible-wavelength switchable emission.

We report switchable emission of visible light at five wavelengths generated in a $\text{YVO}_4$YVO4 cascaded Raman cavity driven by an acousto-optic ${Q}$Q-switched Nd:YAP laser at 1080 nm. The second-harmonic generation and sum-frequency generation of the fundamental, first-Stokes, and second-Stokes waves were realized based on the angle-tuned BBO crystal. The phase-match angle tuning span of a BBO crystal is only approximately 2.3° to allow the frequency mixing to produce five visible wavelengths on demand. At an absorbed pump power of 5.96 W and a pulse repetition frequency of 10 kHz, average output powers of 800, 340, 460, 190, and 326 mW were obtained for 539.9, 567.2, 597.4, 631.0, and 668.5 nm lasers, respectively. The results show that the cascaded Raman laser system with an angle-tuned BBO crystal can provide a convenient and efficient method to achieve wavelength-switchable visible emission for multi-wavelength laser applications.

Greater than 2 kW all-passive fiber Raman amplifier with good beam quality

Abstract We report a 2 kW all-fiberized Raman fiber amplifier with efficient brightness enhancement based on the graded-index fiber. The maximum power output reaches up to 2.034 kW centered at 1130 nm, with a conversion efficiency of 79.35% with respect to the injected pump power. To the best of our knowledge, this is the highest conversion efficiency obtained for any Raman laser system using graded-index fiber. An optimized fiber combiner adopting graded-index fiber as the pigtail fiber was fabricated, enabling the preservation of the seeding brightness in the core-pumped Raman fiber amplifier, and further enhancing the ultimate brightness of the output laser after amplification. At the maximum power output, the beam quality parameter M2 is 2.8, corresponding to a signal-to-pump brightness enhancement factor of 11.2. As far as we know, we obtain the highest brightness enhancement among Raman fiber lasers of over 100 W, and the best beam quality for graded-index Raman fiber lasers of over 150 W.

Investigation of a passively Q-switched Raman laser at 1176 nm with Nd3+:YAG/Cr4+:YAG/YAG composite crystal and a coupled cavity

To reduce the thermal lens effect and increase the efficiency, a composite crystal of Nd3+:YAG/Cr4+:YAG/YAG and a coupled cavity structure were employed in our passively Q-switched YVO4-based Raman laser system. Both the simulation and the experiment results showed that the undoped YAG crystal bonded in the end-face of Cr4+:YAG crystal can speed up the heat transfer of Cr4+:YAG crystal and reduce the temperature difference between its side surfaces and the center significantly, and the coupled cavity structure can improve the laser performance, especially at high pump power. The maximum output power of Raman laser of 0.92 W at 1176 nm was obtained with an optical-to-optical efficiency of 11.51%. The corresponding repetition rate and the pulse width is 53.5 kHz and 3.22 ns, respectively.

Determining optical path difference with a frequency-modulated continuous-wave method.

A technique for determining the optical path difference (OPD) between two Raman beams using a frequency-modulated continuous-wave method is investigated. This approach greatly facilitates the measurement and adjustment of the OPD when tuning the OPD is essential to minimize the effects of the diode laser's phase noise on Raman lasers. As a demonstration, the frequencies of the beat note with different OPDs are characterized and analyzed. When the measured beat frequency is 0.367Hz, the OPD between Raman beams is zero. The phase noise of the Raman laser system after implementation of zeroing of the OPD is also measured.

Generation and application of two-photon Raman laser for manipulation of internal state of Cs atom

Two-photon Raman process (TPRP) is an important technique in controlling the atomic internal states. It plays an important role in quantum manipulation and quantum information process. A reliable Raman laser for specific atom is the first step to demonstrate TPRP and quantum manipulation of an atom. In this paper, we theoretically analyze the two-photon Raman process regarding to Cesium “clock states” |6S1/2, F=4, mF=0 and |6S1/2, F=3, mF=0, and we obtain the dependences of the corresponding Rabi frequency on one-and two-photon detunings and one-photon Rabi frequencies in a realistic multi-level Cesium atom system. We find that to obtain an atom state flopping efficiency of 0.99 the Raman laser power fluctuation should be controlled to be smaller than 3.2%. We also report our simple experimental Raman laser system for TPRP of Cesium atom based on a fiber waveguide phase modulator. The phase modulator is driven by a 4.6 GHz microwave source and the two first-order sidebands with a frequency difference of 9.19 GHz are filtered out by a Fabry-Pérot cavity with a finesse of 48. After an amplitude-modulator-based intensity stabilization system, a total power of 73 μupW with a fluctuation of 2.2% within 90 min is obtained. By applying this Raman laser to a single Cesium atom trapped in a micrometer size far-off resonant trap (FORT), we obtain Raman spectra between Cesium “clock states” |6S1/2, F=4, mF=0 and |6S1/2, F=3, mF=0. The discrepancy between the two-photon resonance frequency and the defined clock frequency 9.192631770 GHz is due to the differential Stark shifts by FORT beam and Raman beams as well as the inaccuracy of the microwave source. By varying the Raman pulse length we also show the corresponding Rabi flopping with a rate of 153 kHz, which is consistent with the theoretical calculation. The obtained state transfer efficiency of 0.75 is much smaller than theoretical expectation 0.99, which is mainly limited by the state initialization efficiency. The Raman laser system reported in this paper is simple and reliable to realize and it provides a reliable method to manipulate the Cesium internal state. Moreover it could also be easily extended to other system for quantum manipulation of other species of atom.

Theoretical and Experimental Study on the Intracavity Optical Parametric Oscillator Pumped in a Raman Laser

A rate-equation-based model is established to describe the behavior of an intracavity optical parametric oscillator (OPO) pumped in an actively -switched Raman laser system. The intracavity photon densities and the initial population inversion density are assumed to be Gaussian distribution. These coupled rate equations are solved numerically. In the experiment, a laser diode end-pumped acousto-optically -switched KTP-OPO pumped by a Nd:YAG/ Raman laser is demonstrated. The output characteristics are studied carefully. And the experimental results about the average output power agree with the numerical solutions.

A two-state Raman coupler for coherent atom optics

We present results on a Raman laser-system that resonantly drives a closed two-photon transition between two levels in different hyperfine ground states of (87)Rb. The coupler is based on a novel optical design for producing two phase-coherent optical beams to drive a Raman transition. Operated as an outcoupler, it produces an atom laser in a single internal atomic state, with the lower divergence and increased brightness typical of a Raman outcoupler. Due to the optical nature of the outcoupling, the two-state outcoupler is an ideal candidate for transferring photon correlations onto atom-laser beams. As our laser system couples just two hyperfine ground states, it has also been used as an internal state beamsplitter, taking the next major step towards free space Ramsey interferometry with an atom laser.

Enthalpic and entropic stages in alpha-helical peptide unfolding, from laser T-jump/UV Raman spectroscopy.

The alpha-helix is a ubiquitous structural element in proteins, and a number of studies have addressed the mechanism of helix formation and melting in simple peptides. However, fundamental issues remain to be resolved, particularly the temperature (T) dependence of the rate. In this work, we report application of a novel kHz repetition rate solid-state tunable NIR (pump) and deep UV Raman (probe) laser system to study the dynamics of helix unfolding in Ac-GSPEA3KA4KA4-CO-D-Arg-CONH2, a peptide designed for helix stabilization in aqueous solution. Its T-dependent UV resonance Raman (UVRR) spectra, excited at 197 nm for optimal enhancement of amide vibrations, were decomposed into variable contributions from helix and coil spectra. The helix fractions derived from the UVRR spectra and from far UV CD spectra were coincident at low T but deviated increasingly at high T, the UVRR curve giving higher helix content. This difference is consistent with the greater sensitivity of UVRR spectra to local conformation than CD. After a laser-induced T-jump, the UVRR-determined helix fractions defined monoexponential decays, with time-constants of approximately 120 ns, independent of the final T (Tf = 18-61 degrees C), provided the initial T (Ti) was held constant (6 degrees C). However, there was also a prompt loss of helicity, whose amplitude increased with increasing Tf, thereby defining an initial enthalpic phase, distinct from the subsequent entropic phase. These phases are attributed to disruption of H-bonds followed by reorientation of peptide links, as the chain is extended. When Ti was raised in parallel with Tf (10 degrees C T-jumps), the prompt phase merged into an accelerating slow phase, an effect attributable to the shifting distribution of initial helix lengths. Even greater acceleration with rising Ti has been reported in T-jump experiments monitored by IR and fluorescence spectroscopies. This difference is attributable to the longer range character of these probes, whose responses are therefore more strongly weighted toward the H-bond-breaking enthalpic process.

Efficient Raman laser system using stimulated Brillouin scattering with different confocal parameters for CH_4

We report the efficient Raman laser system with the wavelength of 1.54 microm from a passively Q-switched Nd:YAG laser with high-pressure methane gas. It has been known that the stimulated Brillouin scattering (SBS) prevents the Raman conversion. The efficiency of the Raman conversion, however, has been greatly enhanced with a specially designed lens to use a backward-stimulated Brillouin in our scheme. The special lens has a focal length of 12 cm, and a maximum conversion efficiency of 51% has been obtained with the first-Stokes energy of 32 mJ and the residual pump energy of 30 mJ at 1,400 psi. Comparing two resonators with different focal lengths of the lenses, we have found that backward-SBS can be greatly enhanced by use of the shorter focal length of 12 cm, and the enhanced backward-SBS helps to increase the conversion efficiency.

High Efficiency Pulse Acetone Liquid Raman Laser Using DCMFluorescent Dye as the Enhancement Medium

Pumped by a frequency-doubled Nd:YAG laser, 10-Hz repetition rate,320-mJ pump energy, and 5.1-ns pulse width, a liquid Raman laser usingacetone as the Raman shifting medium has been established. The residualpump laser pulse and the generated Stokes pulse are directed to a DCMdye cell for energy enhancement of the Stokes pulse. The Raman lasersystem is capable to produce a laser pulse at wavelength 630 nm, withsingle pulse energy of 120 mJ, peak power of 70 MW and an average powerof 1200 mW. The energy conversion efficiency is 37.5%, or equivalentlya quantum efficiency of 44.5%.

A Raman laser system for multi-wavelength satellite laser ranging

In order to develop a laser system for multi-wavelength satellite laser ranging, the joint group of the Shanghai Astronomical Observatory and the Czech Technical University has studied the conversion efficiency of the Raman-shifting beam and its spatial characteristics. We adopted a 0.53 μm laser with pulse width of 35 ps and peak energy of 35 mJ, the second harmonic of a Nd:YAG actively and passively mode-locked laser, to pump a one-meter-long Raman tube which is full of H2 with high pressure at the Prague-based laboratory. We get the first Stokes laser (0.68 μm): 7 mJ (single pulse) with beam divergence of 40″ (arcsecond) and spatial wobbling of less than 4″; and the first anti-Stokes laser (0.43 μm): 2 mJ (single pulse) with divergence of 56″ and spatial wobbling of less than 4″. The emitting beam from the Raman cell also includes 0.53 μm: 10 mJ (single pulse) with divergence of 40″ and spatial wobbling of less than 7″. According to the radar link equation and based on the above obtained multi-wavelength’s energy, we can estimate the detection probabilities for three colors respectively. It is shown by the result that the developed multi-wavelength Raman laser system has the capability of satellite ranging. The Raman laser system will be installed at the laser station in Shanghai Astronomical Observatory to research the multi-wavelength satellite laser ranging.

A Raman laser system for multi-wavelength satellite laser ranging

A Raman laser system for multi-wavelength satellite laser ranging

Global solutions and attractors of a Maxwell-Bloch Raman laser system in two transverse dimensions

We study a Maxwell-Bloch system describing the dynamics of single-longitudinal Raman lasers in the two transverse space dimensions. Raman lasing is generated by a coherent external pump laser, as a three-wave interaction involving two optical and one material wave. On the other hand, a two-level laser involves incoherent external pumping through, for example, an electrical discharge or flashlamp. Raman lasers have the advantage of being tunable and display a novel explicit nonlinear detuning between the pump and laser emission frequencies. Consequently these lasers exhibit much richer nonlinear dynamics. We establish the global existence of classical solutions, and show that for periodic domains the dynamics is governed by a global smooth attractor of finite dimensions. We explain the structures of nonlinear interactions and couplings that lead to the time asymptotic smoothing. We also construct mild solutions with the dispersive Strichartz inequality for rough but spatially decaying data (in , ) on the whole plane, which physically corresponds to the absorbing boundary condition.

Efficient First Stokes Generation Using a Brillouin Resonator Coupled with a Raman Half Resonator

We report an efficient Raman laser system which utilizes stimulated Brillouin scattering as a dual-cavity resonator mirror for fundamental and Raman waves. A Raman laser at the eye-safe wavelength of 1.54 µ m is generated in high pressure CH4 gas from a passively Q-switched Nd:YAG laser. Employing a meniscus lens with an optimized reflectance of 10% at the fundamental wavelength, a maximum Raman energy of 33 mJ with a residual fundamental energy of 20 mJ has been obtained, where the pressure of CH4 gas is 800 psi.

Analysis of the efficiency of a third order cascaded Raman laser operating at the wavelength of 1.24 μm

We report a comparative numerical study of the performances of different linear configurations of a third order cascaded Raman laser CW pumped at the wavelength of 1.064 m by a Nd-doped double clad fibre laser. We compare the maximum conversion efficiencies, slope efficiencies and thresholds of various configurations characterized by different parameters of the fibre, different fibre lengths and third Stokes output couplings to give indications towards Raman laser system optimization.