公司简介

PGL（Plymouth Grating Laboratory）是全球领先的专业的光栅设计和生产公司。PGL 采用SBIL-scanning beam interference lithography方式生产光栅，这种方法可以使得光栅的尺寸比利用传统方法生产的光栅的尺寸有很大的突破。目前，PGL为客户提供的尺寸为91cm x 42cm 的MLD光栅（-- a set of 91cm x 42cm MLD gratings for pulse compression on the University of Osaka's ILE laser），是目前世界最大的光栅。

PGL 于2004年由Douglas Smith和MIT的Kavli 研究院（Kavli Research Institute)Mark Schattenburg 博士 共同成立。公司位于美国麻州的普利茅斯（Plymouth, MA）。

产品介绍

Pulse Compression Gratings 

PGL is currently manufacturing and supplying multilayer coated dielectric (MLD) Gratings to several of the world’s largest ultra high-intensity laser projects. These gratings are made under license to Lawrence Livermore National Laboratory. The combination of coating and grating fabrication makes it possible to greatly improve damage threshold, diffraction effciency, and wavefront of the compressed short pulse. PGL also fabricates gold gratings over photoresist or metal over etched silica for broadband applications.  
A 91cm x 42cm MLD grating for laser pulse compression on the laser at the Institute for Laser Engineering at Osaka University

These gratings are produced on a custom basis. Please call us with your requirements.

Current capacities:

Grating Variations

Since the gratings are written with a small fringe-locked spot many possibilities exist for writing focussing or chirped gratings. Gratings may even be written with a distributed phase function to provide for uniform illumination of larger targets.

2-D Gratings 

2-D Grating shapes for a high contrast fringe pattern as a function of exposure


An etched 2-D Grating Array as seen in a Scanning Electron Micrograph. 
The grating is etched into fused silica and then coated with aluminum.

Grating Fabrication

PGL has demonstrated both high efficiency and high damage threshold. Large aperture gratings have been fabricated and tested with excellent diffraction efficiency >96% into the 1st order. The laser-induced damage threshold has been tested at 600 fs and 10 ps. The results are among the highest ever tested for an MLD grating. 

Gratings written on the Nanoruler have a very flat wavefront when measured in Littrow

GR3 has been written with an excellent result.

The two Littrow measurements, CW and CCW, allow the holographic component (line straightness) to be separated from substrate irregularity. 


Dose Control

The Nanoruler has exceptional control of the dose delivered to the resist. This is seen in an exposure test as seen below. The slowly varying duty cycle is especially important when trying to acheive very high diffraction effciencies. 
Exposure test at 1740 lines/mm on BF/MLD/120ARC/500PR3/5/08 1.3 mm apertures; 178t-08-nr2; Doses 150 to 50 mJ/cm2

   
   
  

Ghost-free grating - Because of the multiple fringe averaging which takes place during scanning, Nanoruled gratings are free from ghosts that form from defects in collimating optics in conventional exposure methods.These ghost can lose energy due to scattering, affect wavefront, and potentially can form hotspots in downstream optics

Grating Design

PGL can model complex grating designs which can include dielectric stacks or metals. 
This design information is provided to the customer if requested.

Gold Grating, S-Polarization

Coating Design

Coating Fabrication

Coating Process Development

PGL develops full coating processes for large optical coaters. A 2 meter chamber here is being prepared with coating processes for complex multilayers and energetic processes such as ion-assisted deposition. 

技术能力

Scanning-Beam Interference Lithography

Gratings are written with Scanning-Beam Interference Lithography (SBIL) using the nanoruler. 

Utilizing an array of custom processing equipment and techniques, PGL can process a wide range of optical substrates.Current maximum size is about 93 cm x 60 cm. Plans are underway to make a machine with 1.3 to 1.5 meter capability 

SBIL produces a highly accurate linewidth that results in excellent diffraction efficiency that is both uniform and repeatable from part-to-part. By precise control of the grating exposure and phase, PGL's SBIL technology is the only known technique that allows for correction of wavefront errors in substrates and apodization of incident beams. The scanning technique of SBIL overwrites with a gaussian distributed energy band of laser light that provides a high level of dose control resulting in consistent aspect ratio, high efficiency, and period repeatability of over 10ppb part-to-part.





PGL and MIT are working toward writing more complex gratings withVariable-Period Scanning-Beam Interference Lithography (VP-SBIL). VP-SBIL capacity allows for a quick changeover for periods from 200 nm to 20 µm. VP-SBIL has been tested at 100, 200, 500, 1000, 1740, 2500 and 5000 lns/mm. Due to the high degree of automation in the tool, period can be changed and ready to write on large samples in < 1 hour. PGL now writes gratings with two or more periods on the surface. Coarse gratings are used for measurement of grating thickness.

Ion Beam Etching

PGL uses a large area reactive ion etcher to etch photoresist gratings into various silicate glasses. 
 
Here a grating is mounted in the etch chamber. The ion source is in the foreground. 

The PGL Ion Etcher uses a scanning method to achieve high etch uniformity. Etched MLD diffraction efficiency is uniform and high across the part. PGL can accurately map diffraction efficiency across large parts to determine etch uniformity.

Sandia Compressors (600mm x 210 mm) 
 
C3 DE Average 0.97

 
C5 DE Average 0.98

 
C1 DE Average 0.965

Liquid Film Coating

PGL's meniscus coater applies photoresist to the substrate. The meniscus coater pulls the substrate over a meniscus of fluid. Small substrates are held upside down by a vacuum while large substrates are held by a groove in the substrate.

Coating

A 1.1 meter chamber is used for development of complex multilayers and energetic processes such as ion-assisted deposition.

• Two electron beam sources
• 12 cm RF Ion Source
• Optical Monitor
• 19" Dia. Planetary Rotation
• Used for development of PGL coating control software "Designlink" 

Large Optic Handling

Coating Tooling is designed to allow thermal expansion of the substrate and tooling without damage to the optic. Handling tooling allow for safe handling of the substrate. 

Special packaging protects substrates from contamination. 

应用领域

Laser Pulse Compression

A 91cm x 42cm MLD grating for laser pulse compression

Gratings for pulse compression have very demading requirements. They must have a 26 to 40 layer multilayer dielectric reflector coating, the devices must operate in a high vacuum, flatness requirements are severe, and laser damage thresholds must be high in the short pulse (0.5 to 10 ps) regime. In these conditions, coating stress must be carefully considered since too much compressive stress will deform the substrate and too much tensile stress will cause coating and substrate crazing.

PGL has developed a low stress coating for silica substrates in cooperation with Osaka University and Okamoto Optics LTD in Yokahama, Japan. High flatness gratings are much easier to produce on silica than other high thermal expansion glasses. The coating process uses ion-assisted deposition to induce the correct amount of film stress to produce a net-zero stress on the device in vacuum. Damage-thresholds of this coating have demonstrated values as high as the best conventional e-beam deposited coatings.

Pulse compressor schematic for the LLE/University of Rochester OMEGA EP

Precision Textured Surfaces

The formation of uniform and repeatable patterns on a nanostructure scale can be produced with the SBIL process. Such patterns on surfaces requiring precise periodic structures of various shapes and geometry can be established directly on substrates as masters and be used to make replicated nanostructered surfaces.Further texturing can be done using ion-etching techniques.

Polarization Control 

200 nm Gratings For LCD Display Wire-Grid Polarizers Wire grid polarizers require a fine array of grating lines etched into silica. PGL has produced these structure with periods as small as 200 nm. We are now working on devices that have even smaller periods and methods to apply these patterns to cylindrical substrates for replication.