ABSTRACT
This paper presents a theoretical and experimental characterization of an instability phenomenon observed in single-frequency fiber amplifiers when the frequency of the seed laser is modulated. The instability manifests itself as fluctuating elastic back-reflections that occur only when the frequency is decreasing with time. The theory is a generalization of a coupled-mode model developed for a single-frequency fiber amplifier back-seeded with a constant frequency shift relative to the main signal. It can explain most observed features of the experiments in a qualitative and semi-quantitative way. Open questions and directions for further developments are also discussed.
ABSTRACT
It is widely acknowledged that the phase noise of an optical frequency comb primarily stems from the common mode (carrier-envelope) and the repetition rate phase noise. However, owing to technical noise sources or other intricate intra-cavity factors, residual phase noise components, distinct from the common mode and the repetition rate phase noise, may also exist. We introduce a measurement technique that combines subspace tracking and multi-heterodyne coherent detection for the separation of different phase noise sources. This method allows us to break down the overall phase noise sources associated with a specific comb-line into distinct phase noise components associated with the common mode, the repetition rate and the residual phase noise terms. The measurement method allow us, for the first time, to identify and measure residual phase noise sources of a frequency modulated mode-locked laser.
ABSTRACT
We report on the observation of unstable two-wave mixing in a Yb-doped optical fiber amplifier induced by frequency modulation of a single-frequency laser. What is believed to be a reflection of the main signal experiences a gain much higher than that provided by the optical pumping and potentially limits power scaling under frequency modulation. We propose an explanation for the effect based on the dynamic population and refractive index gratings formed by the interference between the main signal and its slightly frequency-detuned reflection.
ABSTRACT
A 32 mW fiber laser is stabilized to the (13)C(2)H(2) P(16) (ν1 + ν3) transition at 1542 nm using saturated absorption. The short-term shot-noise limited fractional frequency instability is 5.0 × 10(-13)(τ/s)-½ for averaging times τ up to about 100 s. The relative lock-point repeatability over 2½ month is 4.3 × 10(-13) corresponding to 83 Hz. The simple setup includes a 21 cm long gas cell, but it does not require an enhancement cavity or external modulators. The spectroscopic lineshape is analyzed with respect to optical power and acetylene pressure. Narrow linewidths of 300 kHz FWHM are observed with a signal to noise ratio of 35 dB in a 9 Hz bandwidth.
Subject(s)
Lasers , Equipment Design , Equipment Failure AnalysisABSTRACT
Previous to October 1st, 1981, 8 major Danish anaesthesiological departments registered 105 patients treated with extradural opiates for a period of more than 7 days, partially or completely on outpatient basis. Ninety-four suffered from painful malignant diseases and 11 patients from various painful benign diseases. The mean period of treatment was 65 days (range: 7-283 days) and of these 49 days (2-266 days) as outpatients. The total number of inserted epidural catheters was 215, equivalent of an average of 2 per patient (range 1-5). Reasons for removing an extradural catheter were injection-related pain, difficulty in injecting the desired volume, and displacement of catheter. Morphine chloride, in a solution of 0.4 mg/ml of normal saline, was the main choice as analgesic agent (90 patients). The mean daily dose of this drug totalled 12.6 +/- 4.8 mg (S.D.) (range: 4-30 mg) distributed as 2.7 +/- 0.9 (S.D.) (range: 1-6) daily injections. Twelve patients were treated with buprenorphine extradurally. Satisfactory pain relief was achieved for 70 patients (67%) who managed with extradural opiates as sole analgesic treatment. One patient developed septicaemia with a non-fatal outcome probably originating from some other focus. Apart from this no serious side effects were reported. Medically unskilled persons or relatives were responsible for instillation of all extradural opiates with 42 patients and partially responsible with 14 patients. Eleven patients managed injections without assistance. District nurses took care of medication for 46 patients, aided by a general practitioner in 5 cases. Three patients were supplied with continuous extradural infusion by means of a Mill Hill microinfusion pump.
