Proceedings Volume 1837

Frequency-Stabilized Lasers and Their Applications

Y. C. Chung
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Proceedings Volume 1837

Frequency-Stabilized Lasers and Their Applications

Y. C. Chung
View the digital version of this volume at SPIE Digital Libarary.

Volume Details

Date Published: 30 April 1993
Contents: 13 Sessions, 46 Papers, 0 Presentations
Conference: Applications in Optical Science and Engineering 1992
Volume Number: 1837

Table of Contents

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Table of Contents

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  • Frequency-Stabilized Lasers
  • Frequency-Stabilized Semiconductor Lasers I
  • Other Frequency-Stabilized Lasers
  • Frequency-Stabilized Semiconductor Lasers II
  • Frequency-Stabilized Lasers for Optical Fiber Communications I
  • Frequency-Stabilized Lasers for Optical Fiber Communications II
  • Wavelength-Division-Multiplexed Systems I
  • Wavelength-Division-Multiplexed Systems II
  • Frequency Standards
  • Novel Applications
  • Spectroscopy and Precision Measurement
  • Frequency Synthesis
  • Postdeadline Papers
Frequency-Stabilized Lasers
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Frequency-stabilized lasers: a parochial review
John L. Hall
It is hoped that this article will serve as a useful introduction to the art of stabilized lasers, especially for those who are joining this sport from other fields. It has become clear that pre- stabilization of the laser on the non-saturable resonance of a stable cavity is a good strategy: with adequate feedback system design, one can effectively replace the intrinsic noise of the laser with the measurement noise of the stabilizer system. By now sub-Hertz frequency control and optical phase locking have been demonstrated with most of these tunable sources. The ready access to modulation of the diode laser can lead to a very simple but impressive source, while the external stabilizer approach is attractive for dye and optically pumped solid-state sources. Current work on amplitude-stabilization of the laser pump may lead to reduction of the `intrinsic' solid state laser noise as well. With the current explosion of interest in atom trapping techniques we can look forward to major progress in the narrow-line laser/super- sharp absorber high resolution spectroscopy business. Applications range from atomic clocks to cold atom collision physics to tests of special relativity. The combination of ultra-stable lasers with cold atom interferometry will be especially powerful in offering new tests of atomic charge neutrality and of time reversal invariance via new limits on atomic electric dipole moments. Remarkably, a practical instrument for oil and gas prospecting might be based on a laser-diode/atom-interferometric measurement of local `g'.
Frequency-Stabilized Semiconductor Lasers I
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Frequency locking of diode lasers using metallic vapor optogalvanic spectra
Jean-Marie Gagne
The frequency stabilization of an AlGaAs laser using the linear optogalvanic signal from metallic vapor is reported. A hollow-cathode discharge tube, designed and built in our laboratory, has been used to obtain resonant optogalvanic lines corresponding to Ul and Thl transitions. These results show that the rich optogalvanic spectra of Ul and Thl can be efficiently used for the frequency-locking of semiconductor lasers.
Frequency stabilization and frequency control of a semiconductor laser using the Faraday effect of the Rb absorption line
Takashi Sato, Takao Nakazawa, Takashi Ueno, et al.
The frequency stabilization of a semiconductor laser has usually been performed by applying a small modulation directly to the injection current. This paper reports a few frequency stabilization methods without a direct modulation, i.e., without a frequency broadening. These stabilization methods use the Faraday effect and/or the Zeeman effect of a saturated absorption line of the Rb atoms to obtain a control signal which is feedback to the injection current. These methods provide a better frequency stability and frequency control compared with the method using the direct modulation.
Frequency stabilization of AlxGa1-xAs/GaAs lasers using velocity-selective magnetic-optical activity
W. David Lee, Jason J. Heuring, Joe C. Campbell
Optical feedback from velocity-selective magnetic-optical activity in alkali metal vapors has been shown to be an effective technique for simultaneously stabilizing the frequency and reducing the linewidth of AlxGa1-xAs/GaAs lasers. The ultimate frequency stability of such a laser is limited by the quality factor Q equals (nu) 0/(Delta) (nu) of this frequency reference. In this letter we report the measurement of Q equals 6 (DOT) 106 for optical feedback from velocity-selective magnetic-optical activity in Rb vapor.
Other Frequency-Stabilized Lasers
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Highly stable and high-power Nd:YAG lasers
Kenichi Nakagawa, Yukitaka Shimizu, Takeshi Katsuda, et al.
We describe the design and performance of highly stable and high power Nd:YAG laser system for the interferometric gravitational wave detectors. The frequency of a diode-pumped Nd:YAG laser is stabilized by using a high finesse optical cavity, and its frequency noise is reduced to as low as 1.5 mHz/(root)Hz. Using a high power lamp-pumped ring Nd:YAG laser, single frequency output power of 4 W is obtained, and the injection locking is realized by using a diode-pumped laser as a master laser. We also show the design of high power single frequency diode-pumped Nd:YAG lasers.
Internal-mirror He-Ne laser stabilized to saturated absorption of iodine in an external ring resonator
Fumio Murakami, Kenji Narumi, Tatehisa Ohta
Saturated absorption of iodine was observed using the polarization-stabilized internal-mirror He-Ne laser. An external ring resonator was used to enhanced saturated absorption. The P(33) line provided a sufficient signal to noise ratio for laser frequency stabilization.
Active reduction of frequency jitter in single-frequency ion lasers
John P. Ekstrand, Steven C. Guggenheimer
One of the advantages of commercial ion lasers is their ability to produce high power cw output in a single longitudinal mode. When running in a single longitudinal mode, the short- term frequency 'jitter' (< 1 sec) is determined primarily by cavity vibration induced by water flow in the laser head. Using a piezo electric transducer to control the cavity length, we reduce the water-induced jitter by factors of up to 10.
Frequency-Stabilized Semiconductor Lasers II
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Simultaneous improvement of short- and long-term frequency stability of a diode laser
Utako Tanaka, Tsutomu Yabuzaki
The long- and short-term frequency stability of a diode laser is simultaneously improved by using an external cavity whose resonance frequency is locked to the center of a Doppler-free spectrum of the 85Rb-D2 line without laser frequency modulation. The obtained linewidth of the diode lasers is less than 100 kHz and the long-term stability in terms of the square root of the Allan variance (sigma) monotonously decreases from 2 X 10-12 to 2 X 10-14 as the averaging time (tau) increases from 100 ms to 100 s.
Frequency stabilization of tunable narrow-linewidth external-cavity semiconductor lasers
Hanyi Zhang, Yanjie Chai, Bo Sun, et al.
A strongly coupled external cavity semiconductor laser with stable frequency operation is reported in this paper. The typical linewidth, maximum tuning range and side-mode suppression ratio of the device are 100 kHz, 120 nm and 35 dB, respectively. The operation frequency is quite stable because of adopting strong external cavity feedback, temperature compensation cavity structure and double-stage temperature control. With the aid of active frequency control loop the frequency shift can be limited within several MHz over 24 hours. More than twenty tunable narrow-linewidth external-cavity semiconductor lasers have been developed in China.
Instabilities in a laser diode with strong optical feedback
Jesper Mork, Bjarne Tromborg, V. L. Velichansky, et al.
We present a theoretical and experimental investigation of some of the instabilities encountered when a laser diode is exposed to optical feedback. The main emphasis in the paper is on the low-frequency instability seen for strong feedback levels.
Frequency-Stabilized Lasers for Optical Fiber Communications I
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Review of user requirements and practical possibilities for frequency standards for the optical fiber communication bands
David J. Knight, P. S. Hansell, H. C. Leeson, et al.
This paper reports user requirements for frequency standards for optical communications and reviews physical possibilities for measurement standards to support those needs. A survey of the industrial and regulatory requirements for frequency standards for optical communications was made between October 1991 and January 1992. This was centered on the UK and Europe, but also took in responses from the USA and Japan. Over 70 representatives from 49 organizations were contacted, and a response exceeding 50% was achieved. The main requirement found was a need for two frequency standards per band in each of the 1.5 micrometers and 1.3 micrometers bands, with those in the 1.5 micrometers band needed first, and in the next 3 - 5 years. An accuracy of order 1 part in 109 was desired for laboratory use, with an order of magnitude less for a transfer standard, and an order less again in the field. The physical possibilities for frequency standards in these bands are reviewed, addressing the use of atomic and molecular resonances.
Frequency standards at 1.523 um based on 20Ne and at 1.56-um derived from the 0.780 um Rb frequency standard
David J. Knight, K. I. Pharaoh, Geoffrey P. Barwood, et al.
This paper reports experimental work towards a laboratory standard based on the 20Ne transition at 1.523 micrometers , some calibration measurements to 2.5 parts in 107 on lines of C2H2 between 1.52 and 1.545 micrometers , and investigation of a standard at 1.56 micrometers involving a CO line. Progress is described towards measurement of the latter line by frequency doubling to, and beating against, a Rb D2-line stabilized laser at 0.780 micrometers of known frequency.
1.55-um-band practical frequency-stabilized semiconductor laser using C2H2 or HCN absorption lines
Satoshi Yoshitake, Koji Akiyama, Miyako Iritani, et al.
We developed three types of frequency stabilized semiconductor lasers (LD) source or optical synthesizers using 12C2H2 or H13C14N absorption lines. This paper reports on the three methods below: (1) A frequency stabilized LD source controlled by sinusoidal LD current modulation reduced to lowest possible values. The maximum frequency deviation was +/- 5 MHz. And a frequency stability of 9 X 10-10 (DOT) (tau) -1/2 (0.1 s 12C2H2 absorption line and a frequency stability of less than 1.0 X 10-9 (10 s 13C14N absorption line were obtained from the beat method. (2) An optical synthesizer using two LDs and a newly developed frequency control method. The frequency synthesized range was +/- 2 GHz from the absorption frequency. A short-term frequency stability of about 2 X 10-9 (DOT) (tau) -1/2 (0.1 s -10 (10 s
Observation and characterization of 87Rb resonances for frequency-locking purpose of a 1.53-um DFB laser
Marc Breton, Pierre Tremblay, Normand Cyr, et al.
We report the progress of our work on the observation and the characterization of 87Rb vapor resonances in order to frequency-lock a 1529 nm DFB semiconductor laser. We present energy levels diagrams corresponding to the 5P3/2 yields 4D5/2 and 4D3/2 transitions of rubidium atoms, respectively at 1529.4 and 1529.3 nm (196.02 and 196.04 THz). Basic emission characteristics of our DFB laser are also given. We then show the absorption profiles of a probe laser emitting around 1529 nm while the 87Rb vapor is optically pumped at 780.2 nm (D2 line at 384.2 THz) using a 30 mW AlGaAs laser. We finally present, for this experiment, the dependence of the probe laser absorption resonance depth and linewidth on the pump power.
Frequency-Stabilized Lasers for Optical Fiber Communications II
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Frequency stabilization of a fiber laser to rubidium: a high-accuracy 1.53-um wavelength standard
Sarah L. Gilbert
Spectroscopy of the rubidium 5P3/2 yields 4D5/2 transition near 1.529 micrometers has been performed using a single-longitudinal-mode erbium-doped fiber laser. Rubidium atoms were laser-cooled and confined in a vapor-cell Zeeman optical trap. This produced a dense sample of cold atoms and reduce the Doppler broadening of the transition to less than the natural linewidth. Transition linewidths of 10 MHz were observed on the 5P3/2 yields 4D5/2 transition and the fiber laser was actively stabilized to the 5P3/2, F equals 3 yields 4D5/2, F' equals 3 line of 87Rb.
Frequency stabilization of DFB laser diodes to the P(3) line of acetylene at 1.52688 um by external phase modulation
Fabrizio Bertinetto, Piero Gambini, Roberto Lano, et al.
The emission frequency of DFB laser diodes has been locked to the P(3) line of the roto- vibrational absorption spectrum of Acetylene at 1526.878 nm. An external phase modulator is used to obtain the error signal, thus resulting in absence of frequency modulation on the frequency stabilized output, as well as good short and long term stability. The stability has been evaluated analyzing the beat signal between two independently stabilized lasers.
Frequency-stabilized 1.5-um laser diode using a heterodyne spectroscopy method for a spatial application
Michel de Labachelerie, Christine Latrasse
We have developed 1.5 micrometers DFB lasers stabilized on a C2H2 absorption line. The stabilization method was based on the heterodyne spectroscopy technique using a 350 MHz laser diode current modulation. Two 500 cm3 pigtailed stabilized laser modules with 500 (mu) W useful power at 1540.7 nm were realized and showed a relative frequency stability better than 2.10-10 for observation times between 0.3 s and 300 s.
Frequency-locked long-wavelength lasers for lightwave communication systems
We report a packaged DFB laser frequency-locked to the Kr 1s2 - 2p8 transition at 1.54782 micrometers using a novel miniature discharge lamp. This lamp generates more than an order of magnitude larger optogalvanic signal for the same input power than conventional indicator lamps of comparable size. The frequency stability of the laser package is better than 2 MHz, and the fiber-to-laser coupling loss (< 2 dB) is very stable against temperature fluctuations and mechanical vibrations.
Wavelength-Division-Multiplexed Systems I
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Remote-controlled absolute frequency stabilization of locally independent subscriber lasers for coherent communication systems
Andreas Gladisch, L. Giehmann, Nikolaus Gieschen, et al.
A new double loop frequency stabilization scheme suited for the remote controlled, absolute stabilization of optical carrier in a CMC-LAN will be presented. This concept offers relative carrier stabilization at the transmitter location while the stabilization of all carriers to a common frequency reference is performed at the network center by using an additional low data rate service channel in the optical frequency band. Experimental results for the achieved frequency stability of laser transmitters which are controlled in different manner will be presented and compared to free running lasers.
Multichannel laser frequency stabilization in optical frequency division multiplexing system
Bo Sun, Hanyi Zhang, Shizhong Xie, et al.
Frequency of two distributed feedback laser diodes (DFB LD) are relatively stabilized using a scanning Fabry-Perot Interferometer as a frequency reference, with 10 GHz spacing within 50 MHz fluctuation.
Frequency locking of multiple external-cavity semiconductor lasers with equal frequency span
Yanjie Chai, Hanyi Zhang, Bo Sun, et al.
Frequencies of three 1.52 micrometers external cavity semiconductor lasers were locked to the peaks of a F-P etalon with 4.8 GHz frequency span. The frequency fluctuation between the adjacent channels was less than 10 MHz for long period of observation with laser linewidth of 60 kHz.
Highly accurate frequency counting system for 1.5 um wavelength semiconductor lasers
Motonobu Kourogi, Kenichi Nakagawa, Motoichi Ohtsu
For highly accurate optical frequency measurement in 1.5 micrometers wavelength region, an optical frequency comb (OFC) generator was realized by using a high frequency LiNbO3 electro-optic phase modulator which was installed in a Fabry-Perot cavity. By using the OFC generator, we demonstrated the frequency difference measurement up to 0.5 [THz] with a signal-to-noise ratio higher than 61 [dB], and the heterodyne optical phase locking with a heterodyne frequency of 0.5 [THz] in which the residual phase error variance was less than 0.01 [radian2]. The maximum measurable frequency difference, which was defined as a sideband frequency with the signal-to-noise ratio of 0 [dB], was estimated to be 4 [THz].
Wavelength-Division-Multiplexed Systems II
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Photonic WDM switch using fixed transmitters and tunable receivers
Mario A. Santoro, Kai Y. Eng, Thomas L. Koch, et al.
We discuss experimental results on a photonic switch architecture using dense WDM where laser signals are transmitted at distinct but close frequencies and then summed in a star coupler. The switching function is performed by selecting a particular frequency at each star coupler output. Two types of receivers were implemented: a tunable optical filter followed by a direct-detection receiver and a heterodyne receiver with a tunable laser as local oscillator. To avoid performance degradation due to frequency drifts, the laser transmitters are frequency-locked to a fixed reference frequency comb using a dithering technique with distinct tones. At the receiver side, the tunable filter is computer controlled and locks to the selected channel using the channel dithering tone. Likewise, the heterodyne receiver uses a frequency discriminator in combination with the dithering tone to lock the local oscillator at the appropriate distance from the selected channel.
Ensemble of laser sources with evenly spaced absolute frequencies for optical frequency division multiplexed systems
Michel Tetu, Normand Cyr, Claude Gamache, et al.
Recently we demonstrated a technique to achieve the absolute calibration of a Fabry-Perot resonator used as a multi-frequency discriminator with evenly distributed reference values. These references are used to frequency-lock an ensemble of laser sources to precisely known values. We present in this paper a summary of the procedure that we established and discuss the frequency setting capability and the accuracy of such an optical frequency generator.
Frequency stabilization for multilocation optical FDM networks
Quan Jiang, Mohsen Kavehrad
In a multi-location optical FDM network, the frequency of each user's transmitter can be offset-locked, through a Fabry-Perot, to an absolute frequency standard which is distributed to the users. To lock the local Fabry-Perot to the frequency standard, the standard has to be frequency-dithered by a sinusoidal signal and the sinusoidal reference has to be transmitted to the user location since the lock-in amplifier in the stabilization system requires the reference for synchronous detection. We proposed two solutions to avoid transmitting the reference. One uses an extraction circuit to obtain the sinusoidal signal from the incoming signal. A nonlinear circuit following the photodiode produces a strong second-order harmonic of the sinusoidal signal and a phase-locked loop is locked to it. The sinusoidal reference is obtained by a divide- by-2 circuit. The phase ambiguity (0 degree(s) or 180 degree(s)) is resolved by using a selection- circuit and an initial scan. The other method uses a pseudo-random sequence instead of a sinusoidal signal to dither the frequency standard and a surface-acoustic-wave (SAW) matched-filter instead of a lock-in amplifier to obtain the frequency error. The matched-filter serves as a correlator and does not require the dither reference.
New TDM frequency spacing stabilization scheme for DFB lasers used in FDM systems
Aiguo Li, Yuqiao Liu, Deming Wu, et al.
A new method for channel spacing stabilization to be used in densely packed FDM systems is reported. A periodic step wave signal is applied on a Fabry-Perot interferometer to create a number of equally spaced resonance peaks within one free spectrum range (FSR), and these peaks are used to control the frequency spacing of the transmitter lasers of frequency-division- multiplexing (FDM) systems by time-division-multiplexing (TDM). This new scheme has the capability of frequency-spacing-stabilizing a large number of transmitter lasers and a good frequency spacing stability for practical FDM systems.
Frequency Standards
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Laser cooling and trapping experiments for cesium atoms in NRLM
Takeshi Ikegami, Takayuki Kurosu, Shinichi Ohshima, et al.
Present status of laser cooling experiments in NRLM is presented. Laser cooling and trapping experiments for cesium atoms are continued in NRLM to develop an atomic fountain frequency standard. As a first step, we performed Cs atomic beam deceleration and trapping experiments. Atomic beam cesium atoms were decelerated by counterpropagating radiation from semiconductor laser diodes. The laser frequency was chirped to keep it in resonance with the decelerated atoms. The decelerated atoms were trapped by six mutually orthogonal laser beams in a magneto-optical trap configuration. The atoms could also be trapped directly from ambient cesium gas in a glass cell without using the deceleration laser beam. The characteristics of the trapped atoms are reported.
Improved rubidium frequency standards using diode lasers with AM and FM noise control
Csaba Szekely, R. E. Drullinger
Diode-laser-pumped, rubidium cell frequency standards have potential short-term stability that is vastly better than their lamp-pumped counterparts. However, AM and FM noise in monolithic laser diodes limit their performance. With extended-cavity, grating-feedback diode lasers, the AM and FM noise can be controlled. In the preliminary work reported here, we have used such a laser to make measurements in two different rubidium cell systems. Measured line Q and signal-to-noise ratios corresponding to (sigma) y((tau) ) equals 4 X 10-13 (tau) -1/2 in a commercial, buffer gas type standard and (sigma) y((tau) ) equals 2 X 10-13 (tau) -1/2 in an evacuated, wall-coated cell are demonstrated. We believe both of these numbers can be improved significantly in a fully engineered and optimized standard.
Laser-cooled cesium fountain clock: design and expected performances
Andre Clairon, Phillipe Laurent, A. Nadir, et al.
The use of diode lasers to cool and trap Cesium atoms in a low Cs pressure cell allows the construction of a relatively simple and reliable atomic fountain frequency standard. Here we discuss the design and the potentialities of the Cs clock frequency standards being built at L.P.T.F..
Study on an all-optical microwave frequency standard
Normand Cyr, Michel Tetu, Marc Breton
We describe a simple method to produce a clock transition with purely optical means through modulated pumping. We observe the field-independent ground state resonance of 87Rb atoms using sinusoidal modulation of the injection current of an AlGaAs laser diode emitting at 780 nm (FM modulation). We detect the 6.835 GHz resonance with a modulation frequency of 1.139 GHz. A high contrast resonance peak is observed and a condition for zero light shift is found. With a beam radius of approximately 3 mm and a buffer gas (N2) pressure of 680 Pa (5.1 Torr), a minimal linewidth of 290 Hz is observed. A theoretical study of the excitation of hyperfine coherences by a modulated laser beam is given.
Novel Applications
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Injection-locking mechanisms in semiconductor lasers
Jean-Philippe Bouyer, Christian Breant, Pierre Schanne
Injection locking is known to allow both frequency locking of a slave oscillator and spectral purity transfer from the master to the slave oscillator. In the case of semiconductor lasers, a lot of problems still remain to be explained. Systematic investigation has been realized, both on theoretical and on experimental points of view. Two experiments, using InGaAsP semiconductor lasers, enabled to study precisely phase locking mechanisms and spectral purity transfer from master to slave lasers: the former, with a multimode Fabry-Perot diode laser, coupled to a mirror, as master oscillator. The injection-locked slave laser became monomode like the master laser. The latter, with a DFB laser coupled to a Fabry-Perot interferometer of finesse 300, as master oscillator. The injection-locked slave laser beam had then a 1 kHz linewidth, like the master laser. Moreover, the phase difference between injection-locked slave diode laser and master laser is analyzed over the locking range. This leads to full comprehension of the stability of a diode laser under optical injection, with the possibility of simply calculating all the injection parameters. Besides, this enables to answer the question: 'Are the locking ranges symmetrical or not?'. Fascinating applications of the technique are considered.
Laser-diode-pumped solid state lasers for gravitational wave antenna
The development of frequency stabilized lasers related to the gravitational wave detection is reported. The beat linewidth of laser diode pumped YAG lasers stabilized to the same cavity was measured to be 193 mHz. The source of frequency fluctuation was analyzed carefully. For the higher sensitivity for gravitational wave detection new designs, 100 micrometers thick YVO4 active mirror and virtual source clad pumping YAG lasers are discussed from the view of scaling physics.
Stability measurements of an optically injection-locked microwave oscillator
Christian Beaulieu, Martin Chamberland, Michel Tetu, et al.
Experimental results on the direct injection-locking of a microwave oscillator by an intensity modulated optical signal are presented. Starting with a free-running oscillator, RF spectrum measurements are done as we vary the modulation frequency of the optical signal impinging on the oscillator. The locking range (as much as 5 MHz) is measured for different modulating signal power levels on the laser diode at the fundamental frequency and at the 2nd, 3rd and 5th subharmonics. Frequency stability measurements are conducted in both time domain (Allan variance) and frequency domain (power spectral density). It shows that the phase noise and the long term stability of the microwave oscillator are greatly improved under locked condition. The Allan standard deviation of the microwave oscillator at (tau) equals 0.1 s improves from 10-6 to 10-10 reaching the precision limit of the measurement setup.
Spectroscopy and Precision Measurement
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High-sensitivity spectroscopy with diode lasers
Richard W. Fox, H. G. Robinson, A. S. Zibrov, et al.
Linewidth reduction of an extended cavity diode laser at 657 nm was accomplished by negative feedback to an intra-cavity ADP crystal. High resolution (170 kHz wide) saturated absorption signals were recorded of the calcium intercombination line which is of interest for a frequency standard. The spectrum of the red 62p3/2 - 92s1/2 cesium line in a magneto-optical cell trap was also investigated.
Narrow linewidth visible diode laser at 690 nm: spectroscopy of the SrI intercombination line
Francesco S. Pavone, G. Giusfredi, Annalisa Capanni, et al.
We have investigated the 689 nm intercombination line of SrI using a visible diode laser (emitting at 690 nm) frequency stabilized by means of the extended cavity scheme. Measurements have been performed both in a cell and in an atomic beam.
Doppler-free mid-infrared spectroscopy and direct frequency measurement of a single barium ion transition using a frequency stable ammonia laser
Alan A. Madej, B. G. Whitford, K. J. Siemsen, et al.
The 24.0 THz dipole forbidden, 5d2D3/2 - 5d2D5/2 fine structure transition in a single, trapped, and laser cooled 138Ba+ atom was probed with a tunable sideband from an optically pumped 15NH3 laser. Narrow resonances were observed which showed each Zeeman component to be free of first order and time dilation Doppler effects. Weak motional sidebands were observed adjacent to the central carrier yielding an estimated ion motional temperature below 15 mK. The ammonia laser was stabilized to its sP(8,6) saturated absorption dip, and measurements of the laser output frequency were made with the NRC frequency chain phase-locked to a primary Cs standard. Scanning of the Ba+ D-D resonance with an electro-optically produced sideband of NH3 laser radiation gave a direct measurement of the single ion center frequency. The preliminary series of measurements yielded 24 012 048 309 +/- 17 kHz for the 138Ba+ D-D transition center frequency.
Precise optical frequency references and difference frequency measurements with diode lasers
Steve B. Waltman, Alexander B. Romanovsky, Joseph S. Wells, et al.
Heterodyne methods have been used in conjunction with molecular calculations to accurately determine the wavelengths of more than 35,000 infrared transitions. We have used high speed whisker contract Schottky diodes to extend this technology to the 0.8 micrometers spectral region. Using microwave harmonic mixing we demonstrate that it is possible to detect beat notes between diode lasers to frequencies as high as 400 GHz.
Frequency Synthesis
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Synthesis of the Lyman-alpha frequency of atomic hydrogen
Dieter Meschede, T. Andreae, W. Koenig, et al.
We have constructed a frequency synthesis chain in order to compare the 1s2s Hydrogen transition (Lyman-(alpha) , 2466 THz) with the Methane stabilized He-Ne-laser at 88,4 THz. Phaselocks for all transfer oscillators have been established. The 88 THz line serves as a secondary frequency standard, currently operating at an absolute reproducibility of 2 X 10-12 and a stability of 10-13 at 10 - 100 s integration time. We report on the transfer of this precision to the Lyman-(alpha) frequency of the hydrogen atom, which yields an improved value of the Rydberg constant.
High-level accuracy measurement of the absolute frequency of the red He-Ne/I2 laser stabilized
Jean-Jacques Zondy, M. Abed, Ouali Acef, et al.
We have built an optical frequency synthesis chain starting from our laboratory-measured reference at 29 THz (CO2/OsO4 laser) to measure with a more than 10 fold improved accuracy the frequency of a He-Ne laser locked on a hyperfine transition of Iodine. The result of the measurement of the laser locked on the 'f' component of (127)R11-5 transition is (nu) equals 473 612 353 586.9 +/- 5 kHz. ((Delta) (nu) /(nu) equals 1. 10-11). The uncertainty found is only limited by the reproducibility of that standard laser. Our chain is potentially capable of measuring optical frequencies from the visible to near IR range with an accuracy level of 10-12, which is presently limited by our reference accuracy.
Computer-controlled optical frequency synthesizer
Bernard Glance
We present a digitally tuned optical frequency synthesizer which can randomly access every frequency over nearly one THz bandwidth with a resolution of 20 MHz. The synthesizer is insensitive to frequency drifts of the laser and provides cold-start operation from an optical frequency reference.
High-performance tunable optical parametric oscillator
Dicky Lee, Ngai C. Wong
We report the experimental demonstration of tunable optical frequency division based on an efficient, one-step parametric downconversion process in a potassium titanyl phosphate (KTP) optical parametric oscillator (OPO). Our compact OPO generated two nearly degenerate subharmonic outputs that can be tuned over a 1.5 THz range in the signal-idler beat frequency by crystal angle tuning and cavity length scanning. We achieved continuous tuning of the beat frequency over a range of 0.5 GHz through the use of temperature and electro-optic tuning of the KTP crystal. A tunable optical frequency divider was realized by phase locking the signal- idler beat frequency to an external microwave frequency source, which yielded a beatnote linewidth at the sub-Hz level. The output frequencies of the phase-locked OPO were therefore precisely controlled by the tunable microwave source and the pump frequency. Characteristics of three different OPO cavity designs and their operations are discussed.
Coherent four-wave mixing in laser diodes
Harald R. Telle, Ch. Koch
We have demonstrated four-wave mixing in multiple-quantum-well (MQW) GaAlAs-laser diodes (LD) by injecting two narrow-band signals from optically/electronically stabilized LDs into a mixer LD. S/N-ratios of the heterodyne-detected mixing signals were measured for frequency differences (delta) (nu) between the pump-lasers up to the THz-range being sufficient for phase-coherent optical frequency synthesis. The measured dependence of the mixing signal S/N ratio on (delta) (nu) indicates a intraband population relaxation time T1 <EQ 200 fs. Schemes for dividing an optical frequency interval into two or three equal parts are discussed. Furthermore, all-optical frequency interval bisection is demonstrated for the first time.
Postdeadline Papers
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Frequency noise reduction of visible InGaAIP laser diodes by different optical feedback methods
The emission spectra of several commercial InGaAlP laser diodes operating in the visible range are investigated. Large free-running linewidths on the hundred MHz level and relaxation oscillations at frequencies up to 2 GHz were observed in the field spectra. Linewidth reduction to less than one MHz has been achieved with resonant optical feedback on the cost of strong relaxation oscillations. With a short extended cavity configuration we could get both narrow linewidths on the MHz level and strong damping of the relaxation oscillations. Keeping the cavity length short, stable operation was achieved without any additional anti-reflection coating of the laser diode. A combination of the two methods gave additional strong reduction in the laser linewidth to roughly 50 kHz. To demonstrate the feasibility of the short extended cavity lasers in the visible range, the calcium intercombination line at 657 nm was reported with high resolution using an atomic beam apparatus.
Optically narrowed Rb-stabilized GaAlAs diode laser frequency standards with 1.5 X 10-10 absolute accuracy
Geoffrey P. Barwood, Patrick Gill, W. R.C. Rowley
The development is reported of GaAlAs absolute laser frequency standards, optically narrowed to 12 and 1 in 1010 respectively have been achieved. The absolute frequencies of these laser diodes when stabilized to certain Rb hyperfine components have been measured by interferometric wavelength comparison against the iodine- stabilized 633 nm HeNe laser to a 1 (sigma) uncertainty of 1.5 X 10-10. Currently, these Rb-stabilized diode laser standards have important application in the determination of the absolute frequencies of 1.5 micrometers diode lasers for optical communications, by means of heterodyne comparison against frequency-doubled 1.56 micrometers diode radiation. Additionally we have developed a 780 nm diode swept-frequency heterodyne facility whereby the swept diode can be tracked over several GHz under close control relative to a Rb-stabilized fixed-frequency reference laser. This tracking technique has application in the monitoring of the frequency drift of Fabry Perot reference etalons of the type used in wavelength division multiplexing and diode stabilization. In particular the frequency or length drift of ultra-low-expansion etalons in evacuated enclosures can be monitored to high accuracy. A length resolution of 1 pm on 10 s timescales is possible using this method.
Development of diode and fiber laser sources for a Sr+ trapped-ion optical frequency standard
Geoffrey P. Barwood, C. S. Edwards, Patrick Gill, et al.
The development of an all-solid-state systems of lasers is described for the cooling and probing of strontium ions in a radio-frequency (rf) trap. The Sr+ ions created within the rf trap are laser cooled by repeated cycling on the 422 nm 2S1/2 - 2P1/2 resonance transition. The 422 nm light was generated from a single mode 70 mW 844 nm diode laser, whose output was frequency doubled to 422 nm in a KNbO3 crystal inside a resonant enhancement cavity. Decays from the Sr+ upper resonance level into the 2D3/2 metastable state remove ions from the cooling cycle. This loss was prevented by driving the 1092 nm 2D3/2 - 2P1/2 transition using a Nd3+-doped fiber laser, diode-pumped at 826 nm. The 2S1/2 - 2D5/2 optical 'clock' transition at 674 nm has a natural linewidth of 0.4 Hz and may be probed with an AlGaInP laser diode. The laser diodes at 844 nm and 674 nm are both collimated using a piezo-mounted GRIN rod which also provides longitudinal mode selection. The spectral output is optically narrowed using resonant optical feedback.
Frequency-stability measurements of two nonplanar ring oscillators independently stabilized to two Fabry-Perot interferometers
Nicholas M. Sampas, R. Liu, Eric K. Gustafson, et al.
We have stabilized two 1064 nm Nd:YAG lasers to two independent Fabry-Perot interferometers. The interferometers are housed separate vacuum vessels and independently temperature stabilized. The ultra-low loss mirrors provide cavity finesses of about 200,000 and cavity linewidths of 5 kHz. The servo control systems use the reflected PM discriminator. Fast feedback to control the laser frequency is applied to a piezoelectric transducer, whereas slow control is made possible by temperature-tuning of the laser crystal. Allan variance measurements of the beatnote between the two laser systems are less than 3 X 10-14 for delay times between 0.1 and 1 s.