Laser oscillating bandwidth

Similar results were obtained by De Shazer using a different detection technique, where laser oscillations in the sample were forced to develop from the narrow-band radiation, injected from a second small aperture laser into the sample laser cavity. The interionic transfer allowed the feeding of this narrow-band radiation by ions having frequencies outside this interval. The effeciency of energy extraction within the narrow bandwidth and the degree of depolarization of the laser oscillations parametrize the cross relaxation effects. 

Experiments were performed using a titanium sapphire laser oscillator capable of producing pulses with bandwidths up to 80 nm FWHM. The output of the oscillator was evaluated to make sure there were no changes in the spectrum across the beam and was compressed with a double prism pair arrangement. The pulse shaper uses prisms as the dispersive elements, two cylindrical concave mirrors, and a spatial light modulator (CRI Inc. SLM-256), composed of two 128-pixel liquid crystal masks in series. The SLM was placed at the Fourier plane [5]. After compression and pulse shaping, 200 pJ pulses were used to interrogate the samples. 

Broad band laser oscillation from Coumarin 153 doped ORMOSIL gels was easily obtained in the free-running laser cavity. The laser emission and the luminescence spectrum both peak at nearly the same wavelength as shown in Figure 4. The laser emission peak was at 526 nm with an oscillation bandwidth of approximately 20 nm FWHM. (For comparison, the reported total oscillation bandwidth in ethanol pumped at 308 nm is 75 nm.) The fluorescence spectrum has a broad peak at about 530 nm with a bandwidth (FWHM) of about 80 nm. 

An ultrabroadband infrared laser oscillation has been obtained at 300 K with F2+ colour centres in LiF [25]. Its wavelength range, 850-1040 nm, is almost comparable to the bandwidth of the F2+ luminescence spectrum. Ultrabroad band laser oscillation is of interest in laser spectroscopy and photochemistry. 

Where Avbw is the total oscillating bandwidth. The shortest pulses are therefore generated by the widest frequency distributions, that is, by arranging for a broad gain bandwidth. Only those frequencies in the emission spectrum of the laser material that can be maintained above the lasing threshold will participate in Avbw Dye lasers and some solid-state lasers (titanium-sapphire) have broad spectral outputs and can produce pulse widths significantly lower than 1 ps. Gas lasers have much narrower bandwidths and typically have pulse widths closer to 100 ps. The solid-state Nd YAG laser is intermediate at near 30 ps. 

High-resolution CARS can be also performed with injection-seeded pulsed dye lasers [334, 351]. If the radiation of a single-mode cw dye laser with frequency o) is injected into the cavity of a pulsed dye laser that has been mode matched to the Gaussian beam of the cw laser (Vol. 1, Sect. 5.8), the amplification of the gain medium is enhanced considerably at the frequency co and the pulsed laser oscillates on a single cavity mode at the frequency co. Only some milliwatts of the cw laser are needed for injection, while the output of the single-mode pulsed laser reaches several kilowatts, which may be further amplified (Vol. 1, Sect. 5.5). Its bandwidth Av for pulses of duration At is only limited by the Fourier limit Av = 1 f(27tAt). 

If only the axial modes TEMqo participate in the laser oscillation, the laser beam transmitted through the output mirrors has a Gaussian intensity profile (5.32), (5.42). It may still consist of many frequencies = qcl 2nd) within the spectral gain profile. The spectral bandwidth of a multimode laser oscillating on an atomic or molecular transition is comparable to that of an incoherent source emitting on this transition ... 

Figure 6.7. Temperature dependence of a hypothetical laser diode. Several modes are shown oscillating within the 2-nm bandwidth envelope of this laser the mode spacing and position change somewhat with temperature as well. Note that some longer-wave-length lasers exhibit significant increases in the bandwidth with temperature.

The laser pulses are generated by a Tirsapphire oscillator (Tsunami Spectra Physics) whereby the central wavelength was set to 775 nm with a bandwidth of about 8 nm (FWHM)... 

The laser emission peak from R6G doped ORMOSIL gels occurred at 571 nm with a bandwidth of 4 nm. The laser emisison band is narrower than the FWHM fluorescence band. The doped ORMOSIL sample exhibited a luminescence peak at 565 nm with a bandwidth of 55 nm (FWHM) In contrast to the C153 gel, the solid state rhodamine doped sample did not oscillate over the FWHM range of die fluorescence emission spectrum. The R6G samples exhibited detectable oscillation over a total range of about 38 nm (559 to 587 nm). 

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