We demonstrate the control of neutral fragmentation of methane (CH4) induced by a Ti:sapphire intense laser pulse (800 nm, 40 fs) by using a pump–probe spectroscopy. Enhancement of the fluorescence emission from the neutral radical CH (A2Δ → X2Π) induced by the intense laser field (~1014 W/cm2) is observed when the wavelength of the probe laser pulse is tuned to 400 nm. The phenomena are explained based on excitation enhancement of the super-excited state of the parent molecule resulting in an increase in neutral dissociation of the methane molecules.

Autofluorescence (AF) spectra of colonic normal and adenocarcinoma tissues are measured under excitation of 337 nm and analyzed by multivariate curve resolution alternating least squares (MCR-ALS) method using non-negativity constraint. Collagen, nicotinamide adenine dinucleotide hydrate (NADH) and elastin are identified as the main contributing biomedical components. Fisher’s discrminant anlysis (FDA) on the concentration profiles of the principle components (PCs) shows acceptable sensitivity, specificty and accuracy for discrminanting the adenocarcinoma tissues from the normal tissues. MCR-ALS is a powerful tool for characterzing the spectra profiles of the main biochemical components in neoplasm transformation.

The laser cooling of ytterbium (Yb) atoms needs a 399-nm laser which operates on the strong 1S0 -1P1 transition and can be locked at the desired frequencies for different Yb isotopes. We demonstrate a frequency locking method using the fluorescence spectrum of an Yb atomic beam as a frequency reference. For unresolved fluorescence peaks, we make the spectrum of the even isotopes vanish by using the strong angular-dependence of the fluorescence radiations; the remained closely-spaced peaks are thus clearly resolved and able to serve as accurate frequency references. A computer-controlled servo system is used to lock the laser frequency to a single fluorescence peak of interest, and a frequency stability of 304 kHz is achieved. This frequency-locked laser enables us to realize stable blue magneto-optic-traps (MOT) for all abundant Yb isotopes.

Noninvasive technology for measuring instantaneously two-dimensional (2D) temperature distributions of flame using two-color planar laser induced fluorescence (PLIF) of OH is investigated. A calibration method is researched and developed. This method is based on the calibration experiments with a laminar premixed flame and thermocouple, and avoids complex calculation and uncertainty of the spectrum parameters. Measurements for a flat burner at ambient temperature under atmospheric pressure are also presented; calibration results are used to diagnose a supersonic combustion in scramjet combustor. The conclusion indicates that this method is useful, and a better precision of calibration can be acquired by correcting the line shapes of the spectral lines and lasers.

Wave packet propagation techniques are used to find experimentally reliable laser parameters that yield optimal production. The photoionization and photodissociation dynamics of sodium iodine molecules are interpreted into several channels. Several frequencies are found to be suitable for NaI molecules during the photoionization and dissociation processes. Photon-dressed excited states and electron-dressed ionic continuum states facilitate the search for available laser parameters.

A simple model is developed to study the laser cooling of solids. The condition of laser cooling of a solid is developed. By using some parameters of the Yb3+ ion, which is most widely used in laser cooling, we then calculate the cooling power and the cooling efficiency. In order to make a more precise analysis, the effect of fluorescent reabsorption, which is unavoidable in the cooling process, is discussed using the random walk model. Taking Tm3+ ion as an example, we derive the average number of absorption events and determine the change in quantum efficiency due to reabsorption. Finally, we obtain the red-shift of the fluorescent wavelength and the requirement of sample dimension.