Hai-Pei Liu

Laser-assisted plasma-enhanced chemical vapor deposition of silicon nitride thin film

Abstract Hydrogenated amorphous silicon–nitride (a-Si–N x :H) films with low hydrogen content were deposited using a CO 2 laser-assisted PECVD, or LAPECVD system. This system was based upon a conventional capacitive RF (13.56 MHz) discharge to dissociate both ammonia and silane, but the substrate could be irradiated by a CO 2 laser beam as well. Whether the substrates were heated or not, irradiation with a CO 2 laser beam without wavelength selection effectively reduced the amount of hydrogen bonds in the films. These films were proved to have a larger index of refraction and better surface flatness. Besides, their resistance to corrosion was considerably improved as compared to films grown under a conventional PECVD process. While the resistive heating was replaced by appropriate CO 2 laser irradiation, the absorption of laser beam raised the substrate-thin film temperature up to 50–60°C only. This non-thermal process represented another advantage of our LAPECVD method.

CO2-Laser-Assisted Plasma-Enhanced Chemical Vapor Deposition of Silicon Dioxide Thin Film

The plasma enhanced chemical vapor deposition (PECVD) of silicon dioxide (SiO2) thin films from SiH4 and N2O has been executed with and without CO2 laser illumination. The quality of the film processed under a 10.6 µm CO2 laser was close to that of a film grown when the substrate was heated to 200°C. Since the temperature of the film substrate under CO2 laser illumination was only about 55°C, this method should be helpful in processes where a low thermal budget is required. CO2-laser-assisted PECVD (termed LAPECVD) with a substrate heated to 200°C resulted in a SiO2 thin film with excellent I–V characteristics and surface morphology, as well as a higher refractive index and lower etching rate in BOE solution. Application of this thin film should be explored.

Experimental Verification of Revised Roles Played by Helium and Nitrogen in CO2 Lasers

In one of our previous papers we presented a fast axial flow CO2 laser excited by 150 kHz resonant silent discharge. The optimized gas mixing ratio of this setup was CO2 : N2 : He = 1 : 22 : 5. This ratio was very peculiar but the laser efficiency thus achieved was optimized and comparable to that of other fast axial flow CO2 lasers. We have already put forth some preliminary postulations explaining the reason for this particular result; nevertheless in order to obtain a clearer insight into this laser we designed and carried out a series of experiments. The data collected were helpful for understanding why N2 is more important than He, and what roles they play in such a laser system.

Sub-Doppler Spectroscopy of Molecular Iodine at 531 nm Using a Frequency-Doubled α-Distributed Feedback Laser

We report, for the first time, the observation of the iodine hyperfine transitions at 531 nm using a frequency-doubled α-distributed feedback (α-DFB) laser. The moderate high power of the α-DFB laser allows us to generate the second harmonic light by a periodically-poled LiNbO3 single-pass frequency doubler. We can stabilize this laser frequency to the hyperfine component a10 of R(94) 34-0 or R(70) 33-0 I2 line, and the preliminary frequency stability was about 5×10-11. This laser system is an attractive frequency standard at 531 nm due to its compact size, high reliability, and low cost.

Frequency modulation spectroscopy of iodine at 532 nm using a vibrating mirror

We demonstrate a simple and low cost method to observe the frequency modulation (FM) saturated absorption spectrum of /sup 127/I/sub 2/ at 532 nm. We use a vibrating mirror with modulation frequency of 570 kHz to modulate the laser frequency. Preliminary result is shown for the iodine P(54) 32-0 line.

Frequency stabilization of an internal-mirror 1.523 /spl mu/m longitudinal Zeeman He-Ne laser

The polarization properties of an internal-mirror 1.523-/spl mu/m He-Ne laser under an axial magnetic field were investigated. When the magnetic field was around 12 mT, we could stabilize the laser frequency at either the center of gain profile or the symmetric two-mode position, and the stability achieved was better than 1 MHz.

Compact laser sources for photorefractive research

Phase conjugate phenomenon and mechanism with BaTiO3 photorefractive crystals have been investigated using various cw sources and all the way down with ultrashort pulses of the femtosecond region. Our laser sources support all the various pulsewidths at a wide range of different spectral regions.

Polarization Properties and Frequency Stabilization of an Internal-Mirror 1523 nm He-Ne Laser under Axial Magnetic Field

The polarization properties of an internal-mirror 1523 nm He–Ne laser under an axial magnetic field were investigated. When the axial magnetic field was around 12 mT, the laser operated in single mode with two opposite circularly polarized components near the center of gain profile. In addition, due to the competition between these two opposite circularly polarized components, each mode had only one circularly polarized component survived when the laser operated in the two-mode region. We could stabilize the laser frequency at either the center of gain profile or the symmetric two-mode taking advantage of the power difference between the two circularly polarized components of the laser output, and the stability achieved was better than 1 MHz.