High resolution lineshape spectra and ultra sensitive noise analyzers for narrowband lasers

Linewidth Analyzer

LWA Series

The HighFinesse Linewidth Analyzers are the ultimate high-end instruments for measuring, analyzing and controlling frequency andintensity noise of lasers. The superb sensitivity of these instruments is achieved by combining an interferometric working principle with high-end optical and electronic components.

The main features are:

Frequency noise density, optical lineshape and relative intensity noise (RIN) analysis with evaluation of intrinsic (Lorentzian) and effective (optical) linewidth

Intrinsic (Lorentzian) linewidth measurements down to 350 Hz

Effective (optical) linewidth measurement range down to 1 kHz

Frequency noise density floor down to 5 Hz/√ Hz with a dynamic range of 60 dB between 10 Hz and 10 MHz

RIN measurement down to −150 dB/Hz

Robust against acoustic noise

Error signal generator for further linewidth, frequency noise or RIN reduction

Powerful tool for a detailed analysis of noise sources like servo bumps, frequency drifts, power supply noise and acoustics

Extremely fast analysis: up to real time measurements and evaluation

The laser lightThe laser light is coupled to the input fiber and lead is coupled to the input fiber and lead through an interferometerthrough an interferometer acting as a frequency acting as a frequency discriminator. The transmitted intensity, which is directly discriminator. The transmitted intensity, which is directly proportional to the variations of the input frequency, proportional to the variations of the input frequency, is converted by a photodetectoris converted by a photodetector and our analog elec-and our analog elec-tronicstronics into a voltage signal. This voltage is finally into a voltage signal. This voltage is finally digitized by the Digitizerdigitized by the Digitizer to provide the data for eval- to provide the data for eval- uation on a computeruation on a computer ..

The included software recovers the original frequency The included software recovers the original frequency noise using the precisely known interferometer function.noise using the precisely known interferometer function.

The recovered timeseries of the frequency deviations The recovered timeseries of the frequency deviations is now the basic dataset allowing to calculate easily is now the basic dataset allowing to calculate easily the frequency noise density spectrum and the optical the frequency noise density spectrum and the optical lineshape spectrum.lineshape spectrum.

The user can also export the timeseries data in order The user can also export the timeseries data in order to perform custom evaluation methods such as Allan to perform custom evaluation methods such as Allan deviation or coherence time analysis.deviation or coherence time analysis.

LaserLaser

Frequency Frequency discriminator discriminator (interferometer)(interferometer)

PhotodetectorPhotodetector

Analog electronics Analog electronics

Data acquisition systemData acquisition system

ComputerComputer

00010000 00100011 1111101111110011 10100011 1111001110010001 11100011 1001000110010111 10100011 1111001111010100 00010000 1111101111110011 10100011 1111001110010001 11100011 1001000110010111 10100011 1111001100010000 00100011 1111101111110011 10100011 11110011

Frequencynoise

Δν

Intensitynoise

Δ I

Δν

ΔI

Δν[Hz]

t[s]

S N [H

z/√H

z]

F (Δν(t

)) × F*(Δ

ν(t))

F (ei2π ∫ Δ

ν(t)d

t ) × F*(e

i2π ∫ Δν(t

)dt )

f [Hz]

Frequency noise density Lineshape (optical spectrum)

Frequencydeviations

Δν [Hz]

L [d

B/H

z]

User defined evaluation:User defined evaluation:

Allan deviation Allan deviation Coherence time Coherence time … …

ΔU

Δν

Voltagenoise

Δ U

Typical Data and Linewidth Evaluation

Timeseries Frequency noise density spectrum

Comparison: Discriminator- vs. Delay-line-technique

β-separation line

Area of frequency noise above β-separation line → Integration for effective (optical) linewidth estimation

White noise level → Noise density level directly proportional to intrinsic (Lorentzian) linewidth

Linefit to optical spectrum → Full width at half maximum = effective (optical) linewidth

DBR laser ECDL @ 1550 nm Fiber laser

LWA-1k 1550Typical frequency noise density spectra

LWA-1k 1550 Typical lineshape spectra

Principle

Limits

Basic data

Frequency noise density

Lineshape

Linewidth evaluation

Direct frequency noise to intensity conversion

Steepness of discriminator-function

Frequency deviations in time

By a Fourier analysis of the frequency deviations

By a Fourier analysis of the calculated electric fields

Effective (optical) and intrinsic (Lorentzian) linewidths directly accessible via frequenvy density noise spectrum or lineshape spectrum

Discriminator (e.g. LWA-1k)

Optical delayed superposition by different path lengths

Length of delay path

Spectrum of beat note (convolution of original spectrum)

Not possible without additional techniques

Lorentzian part (intrinsic linewidth) of the lineshape

Only the Lorentzian part of the linewidth is accessible, because the frequency noise is high- passed by the delay line

Delay-line approach

Freq

uenc

y no

ise

dens

ity

[Hz/

√Hz]

Frequency [Hz]

101

10 –1

10 0

101

102

103

104

102 103 104 10 5 10 6 107

Beside the frequency discrimination approach, homo- and heterodyne delay-line techniques are commonly used for linewidth determination. However, using optical delay lines can lead to complex spectra with non-trivial evaluation needs due to the technique inherent loss of information.

Time [s]

Freq

uenc

y de

viat

ions

[Hz]

0.5 6

0

0.5 -6

1.0 -6

1.0 6

0.00 0.02 0.04 0.06 0.08 0.10

Pow

wer

den

sity

[dB/

Hz]

Frequency [Hz]

10 –5

10 –4

10 –3

10 –2

10 –1

10 0

0 1 M–3 M 2 M–2 M 3 M–1 M

Optical lineshape spectrum

Frequency noise density spectrum from LWA-1k

The delay lines are not long enough to resolve the ultra low frequency noise of the fiber laser.

The delay lines filter out significant parts of the frequency noise of the Ti:Sapphire laser.

Calculated spectra from delayed super-position of electric fields

3.5 µs delay; 20 µs delay; LWA-1k lineshape (one side)

Fiber laser @ 1550 nm

The measurement results of a homodyne delay line detector can be simulated using the time-frequency deviation data of the LWA. The graphs below show this comparison for a Ti:Sapphire (813 nm) and a fiber laser (1550 nm) for two

different lengths of the delay line ( 3.5 µs, 20 µs). The evaluated data (one side of optical spectrum) of the LWA-1k is shown as black curve.

Ti:Sapphire @ 813 nm

1 1510 0.5 85

Technical Data

Frequency Noise Specification

Lineshape Specifications

Miscellaneous

Digitizer Module

Product Overview

Unit

Wavelength range

Input power range (@typical wavelength)

Required input power stability

Laser type

Input type

Maximum frequency stroke (@ f > 10Hz)

Noise floor @typ.input power and wavelength

Frequency noise bandwidth

Dynamic range

Dynamic range

Minimum measurable intrinsic linewidth(lorentzian linewidth)

Effective linewidth range (optical linewidth)[β-separation method]

Effective linewidth range (optical linewidth) [curve fitting method]

Interface

Analog Output

Cutoff (highpass filter)

Dimensions

Weight

Relative intensity noise limit(lorentzian linewidth)

nm

mW

%

MHz

Hz/√Hz

Hz

dB

dB

Hz

mm

kg

Hz

Hz

Hz

dB/Hz

Hz

± 5

10 – 10 M10 – 10 M 2) 10 – 10 M 2)

60

60

< 3 k

< 10 k – 20 M

< 10 k – 10 M

USB 2.0 Type B

BNC ± 7.5 (50 Ω) ± 15 (high impedance) V, single ended

10, 1k, 10k, 100k

220 × 334 × 96

8.0

– 150

< 12 k

< 20 k – 30 M

< 20 k – 10 M

Ethernet

10

440 × 340 × 155 mm

12

–

< 2 k

< 5 k – 30 M

< 5 k – 10 M

Ethernet

10

440 × 340 × 155 mm

12

–

< 10 k

< 15 k – 100 M

< 15 k – 10 M

Ethernet

10

440 × 340 × 155 mm

12

–

< 350

< 1 k – 20 M

< 1 k – 10 M

USB 2.0 Type B

10, 1k, 10k, 100k

220 × 334 × 96

8.0

– 150

Laser type CW, single mode

PM-FC/APC

30

FC/APC

40

PM-FC/APC

30

FC/APC

40

FC/APC

100

min maxtyp

LWA-1k 780 1)

10

200

100

75

1k

30

10k

30

100k

25

> 1M

15

min maxtyp

LWA-10k VIS 1)

10

500

100

150

1k

60

10k

60

100k

50

> 1M

30

min maxtyp

1530

0.5

1625

8

1550

5

LWA-1k 1550

10 100 1k 10k 100k > 1M

80 40 15 10 8 5

min maxtyp

1064

0.5

1625

8

1550

5

LWA-10k NIR

10 100 1k 10k 100k > 1M

200 100 30 20 15 10

min maxtyp

1064

0.5

1625

8

1550

5

LWA-100k NIR

10 100 1k 10k 100k > 1M

1k 200 60 50 40 25

760 1064 2)780 450 1064 2)780

Linewidth Analyzer · 1-2022 · This document provides general information only and may be subject to change at any time without prior notice.

Feedback Controller

Due to the design of the LWAs, the outputvoltage can be directly used as an error signal for a feedback controller allowing to reduce the frequency noise of the test laser.

Depending on the used feedback controller and the laser system the optical linewidth can be reduced by more than two orders of magnitude offering a vast amount of new opportunities.

Feedback controller Feedback controller

Laser Laser

Active laser noise reduction

Connect the Analyzer output signal as input signal to a fast feedback controller.

Connect the feedback controller to the laser’s fast DC modulation input (e.g. laser diode current).

Adjust the feedback to minimize the output signal of the Analyzer (e.g. PID parameters, gain)

Typical application

Laser module quality control

Laser design optimization

Metrology and quantum technology

Linewidth control for spectroscopy

Modulation surveillance

Sample rate

Acquisition time (time series)

Dimensions

Resolution

Communication

Evaluation time 3)

Weight

1) Frequency noise and lineshape specifications are derived from measurements at 780 nm.

2) From 900 nm to 1064 nm the frequency noise bandwidth is limited to 10 Hz to 100 kHz.

3) Effective linewidth: Combination of intrinsic linewidth and additional broadening mechanisms (thermal, electronical and acoustic noise). Determination by β-separation method (noise density spectrum) or curve fitting procedure (lineshape spectrum).

Sa/s

s

mm

bits

s

kg

62.5 M (max.)

1 m – 100 m

210 × 200 × 74

16

USB 3.0 Type B

10 m – 1 (typ.)

2.0

HighFinesse GmbHHighFinesse GmbHWöhrdstraße 4Wöhrdstraße 472072 Tübingen, Germany72072 Tübingen, Germany

Linewidth Analyzer 1-2022 · This document provides general information only and may be subject to change at any time without prior notice.

T + 49 (0) 7071 - 53 918 0T + 49 (0) 7071 - 53 918 0F + 49 (0) 7071 - 53 918 99F + 49 (0) 7071 - 53 918 99M info@highfinesse.comM info@highfinesse.com

Additional informationAdditional informationand distributors:and distributors:www.highfinesse.comwww.highfinesse.com

HighFinesse Precision Current HighFinesse Precision Current Sources have been developed Sources have been developed for experiments and quantum for experiments and quantum technologies in the areas of technologies in the areas of Cold atom physics and solid- Cold atom physics and solid- state-physics. The linearly state-physics. The linearly regulated BCS (Bipolar Current regulated BCS (Bipolar Current Source) and UCS (Unipolar Source) and UCS (Unipolar Current Source) series deliver Current Source) series deliver highly stable, low noise source highly stable, low noise source currents for high precision mag-currents for high precision mag-netic field control. The current netic field control. The current output is floating or is on a user output is floating or is on a user defined potential. Ultrafast re-defined potential. Ultrafast re-sponse to control signals and sponse to control signals and trigger functions, clear grounding, trigger functions, clear grounding, connection and signal isolation connection and signal isolation schemes make the integration of schemes make the integration of the current sources into complex the current sources into complex experimental systems easy.experimental systems easy.

PrecisionPrecisionCurrent SourcesCurrent SourcesSpectrometer OSASpectrometer OSA

HighFinesse/Ångstrom offers sen-HighFinesse/Ångstrom offers sen-sitive and compact wavelength sitive and compact wavelength meters with a large spectral range meters with a large spectral range for high speed measurement of for high speed measurement of lasers. The optical unit consistslasers. The optical unit consistsof temperature-controlled Fizeau-of temperature-controlled Fizeau-based interferometers that are based interferometers that are read out by photodiode arrays. read out by photodiode arrays. The high absolute accuracy is The high absolute accuracy is achieved by use of solid state, achieved by use of solid state, non-moving optics. The optical non-moving optics. The optical unit and associated electronics unit and associated electronics are housed in a compact, thermal are housed in a compact, thermal casing. The connection to a com-casing. The connection to a com-puter or notebook is realized via puter or notebook is realized via a highspeed USB 2.0 port, which a highspeed USB 2.0 port, which allows a high data read-out rate. allows a high data read-out rate. The analyzing software displays The analyzing software displays all the interferometer information.all the interferometer information.

Wavelength MeterWavelength Meter

The grating based HighFinesse/The grating based HighFinesse/Ångstrom Laser Spectrum Ångstrom Laser Spectrum Analyzers offer the capability for Analyzers offer the capability for a very accurate simultaneous a very accurate simultaneous measurement of both the center measurement of both the center wavelength and the linewidth wavelength and the linewidth of a laser source with a compact of a laser source with a compact and versatile instrument.and versatile instrument.

The product series covers the The product series covers the ranges from 192 nm to 110000 ranges from 192 nm to 110000 nm. The grating based technol-nm. The grating based technol-ogy allows the analysis of laser ogy allows the analysis of laser sources over a large linewidth sources over a large linewidth range. Utilizing the principle range. Utilizing the principle of non-moving parts just like of non-moving parts just like the well-known HighFinesse the well-known HighFinesse WS-series wavemeters, the LSA WS-series wavemeters, the LSA offers the time-tested robust-offers the time-tested robust-ness and ability to measure both ness and ability to measure both pulsed and cw lasers.pulsed and cw lasers.